A STUDY OF THE THERMAL DECOMPOSITION OF SOME
HYDRATED COORDINATION COMPOUNDS
by
ROBERT EARL GATHERS, B . S , , M.S.
A DISSERTATION
IN
CHEMISTRY
Submitted t o t h e Graduate Faculty
of Texas Technological College
i n P a r t i a l F u l f i l l m e n t of
the Requirements for
t h e Degree of
DOCTOR OF PHILOSOPHY
Approved
Accepted
May,
1 9 ^
T3
A/o.4
ACKNOWLEDGMENTS
I am indebted to Professor Wesley W. Wendlandt for his direction
of this work, and to the other members of my committee. Professors
Joe Dennis, Arthur L. Draper, Gordon Fuller, Emmett Hazlewood, and
Robert G. Rekers, for their helpful criticism.
I am also indebted to my wife, Jackie, for her encouragement
and help during the preparation of the dissertation.
Acknowledgment is also due the Division of Research, United
States Atomic Energy Commission, Washington, D. C , for their financial support during the course of this investigation.
TABLE OF CONTENTS
LIST OF TABLES
vi
LIST OF FIGURES
vii
I.
II.
INTRODUCTION
1
EXPERIMENTAL PROCEDURE
2
Materials
Method of P r e p a r a t i o n of Complexes
2
. . . . .
2
The Isomeric Chromium(III) Chloride
6-Hydrates
The Hexamethylenetetramine Metal Complexes
Methods of Analysis
Analysis of Chromium i n the Chromium(III)
Chloride 6-Hydrates
Analysis of Metal Content i n Hexamethylenet e t r a m i n e Complexes
2
»•
5
5
5
Analysis of Chloride i n the Chromium(III)
Chloride 6-Hydrates
5
Analysis of Halide Ions i n Hexamethylenet e t r a m i n e Complexes
6
Analysis for Nitrogen
6
I n s t r u m e n t a l Methods
7
Thermogravimetrie Studies i n Air
7
Thermogravimetrie S t u d i e s in VaoKO
7
D i f f e r e n t i a l Thermal Analysis and Gas
Evolution S t u d i e s
8
Reflectance Spectroscopy S t u d i e s
8
X-Ray D i f f r a c t i o n S t u d i e s
8
Magnetic S u s c e p t i b i l i t y S t u d i e s
iii
9
III.
Calorimetric Studies
10
Hydrogen C h l o r i d e E v o l u t i o n S t u d i e s
11
Thermal I n f r a r e d S p e c t r o s c o p y S t u d i e s
13
THE THERMAL DECOMPOSITION OF THE CHROMIUM(III)
CHLORIDE HEXAHYDRATES
16
Review o f t h e L i t e r a t u r e
16
Experimental Results
18
Analytical Results
18
Thermogravimetric Studies in Air
18
T h e r m o g r a v i m e t r i c S t u d i e s in
22
Vacuo
X-Ray S t u d i e s
24
D i f f e r e n t i a l Thermal A n a l y s i s and Gas
Evolution Studies
2^
Reflectance Spectroscopy Studies
29
Hydrogen C h l o r i d e E v o l u t i o n S t u d i e s
29
D i s c u s s i o n and C o n c l u s i o n
IV.
40
THE DEHYDRATION OF COBALT(II) CHLORIDE AND
BROMIDE HEXAHYDRATES
43
Review of t h e L i t e r a t u r e
43
Experimental Results
45
Reflectance Spectroscopy Studies
45
Dynamic R e f l e c t a n c e S t u d i e s
48
D i s c u s s i o n and C o n c l u s i o n
V.
54
THE THERMAL DECOMPOSITION OF SOME HYDRATED
HEXAMETHYLENETETRAMINE METAL COMPOUNDS
56
Review of t h e L i t e r a t u r e
55
Experimental Results
58
iv
Analytical Results
58
Thermogravimetric Studies in Air
58
Thermogravimetric Studies in Vacuo
67
Infrared Spectroscopy Studies
72
Calorimetric Studies
74
Magnetic Susceptibility Studies
78
Reflectance Spectroscopy Studies
78
Discussion and Conclusion
LIST OF REFERENCES
102
107
LIST OF TABLES
Table
I.
Analytical Results
19
X-Ray D i f f r a c t i o n Data
25
III.
Analytical Results
59
IV.
Anedytical R e s u l t s
60
Heats of Dehydration
79
Magnetic Moments
80
II.
V.
VI.
VI
LIST OF FIGURES
Figures
1.
Hydrogen Chloride Evolution Apparatus
12
2.
Thermal I n f r a r e d Spectroscopy Apparatus
14
3.
TGA Curves, Air-Atmosphere
20
4.
TGA Curves, Air-Atmosphere
21
5.
TGA Curves, in Vacuo
23
6.
D i f f e r e n t i a l Thermal Analysis and Gas Evolution Curves . .
26
7.
D i f f e r e n t i a l Thermal Analysis and Gas Evolution Curves . .
27
8.
D i f f e r e n t i a l Thermal Analysis and Gas Evolution Curves . .
28
9. . Reflectance Spectra
30
10.
Reflectance S p e c t r a
31
11.
Reflectance S p e c t r a
32
12.
Hydrogen Chloride Evolution Curves
33
13.
Hydrogen Chloride Evolution Curves
34
14.
Hydrogen Chloride Evolution Curves
35
15.
Hydrogen Chloride Evolution Curves
37
16.
Hydrogen Chloride Evolution Curves
38
17.
Hydrogen Chloride Evolution Curves
39
18.
Reflectance S p e c t r a
46
19.
Reflectance S p e c t r a
47
20.
Reflectance S p e c t r a
49
21.
Reflectance S p e c t r a
50
22.
Dynamic Reflectance Curves
52
23.
Dynamic Reflectance Curves
53
VI1
Figures
24.
TGA Curves, Air-Atmosphere
61
25.
TGA Curves, Air-Atmosphere
63
26.
TGA Curves, Air-Atmosphere
65
27.
TGA Curves, in Vacuo
68
28.
TGA Curves, in Vacuo
70
29.
TGA Curves, in Vacuo
71
30.
I n f r a r e d Absorption S p e c t r a
73
31.
D i f f e r e n t i a l Scanning Calorimeter Curves
75
32.
D i f f e r e n t i a l Scanning Calorimeter Curves
76
33.
D i f f e r e n t i a l Scanning Calorimeter Curves
77
34.
Reflectance S p e c t r a
81
35.
Reflectance S p e c t r a
82
36.
Reflectance Spectra
84
37.
Reflectance S p e c t r a
85
38.
Reflectance S p e c t r a
86
39.
Reflectance S p e c t r a
88
40.
Reflectance S p e c t r a
89
41.
Reflectance S p e c t r a
90
42.
Reflectance S p e c t r a
92
43.
Reflectance S p e c t r a
93
44.
Reflectance S p e c t r a
94
45.
Reflectance S p e c t r a
95
46.
Reflectance Spectra
96
47.
Reflectance S p e c t r a
98
48.
Reflectance S p e c t r a
99
• • •
Vlll
**9,
Reflectance Spectra
lOo
50.
Reflectance Spectra
lOi
IX
CHAPTER I
^ INTRODUCTION
Complexes which contain water as a coordinating ligand generally undergo thermal deaquation by the loss of molecular H2O and the
subsequent f i l l i n g of vacated coordination positions by other a v a i l able l i g a n d s .
Such a mechanism i s n o t , however, a l l - i n c l u s i v e .
A
number of factors are known to effect the mode of deaquation, two of
the most important being the oxidation s t a t e and the e l e c t r o n i c configuration of the coordinating metal.
Metals in higher oxidation
s t a t e s often serve as Lewis acids and undergo s o l i d s t a t e hydrolysis
reactions.
Metals with more than one stable coordination s t r u c t u r e
may even undergo changes in coordination number during deaquation.
Although there have been a large number of investigations concerning the thermal decomposition of hydrated coordination complexes,
only a small fraction of these studies have been extensive in n a t u r e .
Investigations involving complexes which undergo hydrolysis or change
in s t r u c t u r e during deaquation have, for the most p a r t , been limited
t o the determination of heats of dehydration and thermogravimetric
studies.
I t i s the purpose of t h i s investigation t o study in g r e a t e r
d e t a i l some of these metal s a l t hydrate systems.
The systems studied
are the isomeric chromium(III) chloride 6-hydrates, c o b a l t ( I I ) chloride and bromide '6-hydrates, and some hydrated hexamethylenetetramine
metal complexes.
CHAPTER II
EXPERIMENTAL PROCEDURE
Materials
The hexamethylenetetramine was obtained from Merck and C o . ,
Inc.,
of Rahway, New J e r s e y .
The A n a l y t i c a l Reagent grade q u a l i t y MnCl2*4H20, NiS0i^»6H20,
Cr(N03)3-9H20, NiCOa, NiS0^•6H20, NiCl2«6H20, ZnCla, HgCl2, and
CuCl2'2H20 were obtained from t h e J . T , Baker Chemical C o . , P h i l l i p s b u r g , New J e r s e y .
A n a l y t i c a l Reagent grade q u a l i t y Ni(N03)2*6H20, CoS0i»»7H20,
Co(N03)2*6H20, CrCl3«6H20, CoCl2*6H20, and Col2'6H20 were o b t a i n e d
from t h e Mallinckrodt Chemical Works, S t . L o u i s , Missouri.
C o b a l t ( I I ) bromide 6-hydrate and cadmium c h l o r i d e 4 - h y d r a t e ,
a l s o of A n a l y t i c a l Reagent grade q u a l i t y , were o b t a i n e d from F i s h e r
S c i e n t i f i c C o . , F a i r Lawn, New J e r s e y .
Method of P r e p a r a t i o n of Complexes
The Isomeric Chromium(III) Chloride 6-Hydrates
The hexaquochromium(III) c h l o r i d e , CCr(H20)6]Cl3, was prepared
from chromium(III) n i t r a t e 9-hydrate by t h e method d e s c r i b e d by
Bjerrum(l).
F i f t y grams of Cr(N03)3»9H20 was d i s s o l v e d i n 50 ml of
w a t e r and an e q u a l volume of c o n c e n t r a t e d h y d r o c h l o r i c a c i d was
added.
The s o l u t i o n was cooled t o 15®C and maintained a t o r below
t h i s t e m p e r a t u r e while being s a t u r a t e d with hydrogen c h l o r i d e g a s .
The r e s u l t i n g p r e c i p i t a t e was then washed with acetone and d r i e d over
s u l f u r i c a c i d in
vacuo.
Both t h e chloropentaquochromium(III) c h l o r i d e 1 - h y d r a t e ,
CCr(H20)5]Cl Cl2*H20, and t h e d i c h l o r o t e t r a q u o c h r o m i u m ( I I I )
chloride
2 - h y d r a t e , CCr( H2O) 1*012 ]C1»2H20, were prepared from commercial
CrCl3»6H20 as d e s c r i b e d by Bjerrum(2).
The dark green isomer, CCr(H20)^Cl2]Cl•2H20 was prepared by d i s s o l v i n g 50 grams of commercial CrCl3*6H20 (a mixture of t h e t h r e e
isomers) i n 50 ml of w a t e r , f i l t e r i n g , and c o o l i n g i n an i c e bath b e low 0°C.
This temperature was maintained while t h e s o l u t i o n was s a t -
u r a t e d with hydrogen c h l o r i d e gas and then allowed t o s t a n d f o r a
few h o u r s .
The product was f i l t e r e d and d r i e d i n a d e s i c c a t o r f o r
two d a y s .
The c r y s t a l s were then washed with s u c c e s s i v e amounts of
acetone and d r i e d a t ambient t e m p e r a t u r e s .
The p a l e green isomer, CCr(H20)5Cl]Cl2'H20, was obtained by
b o i l i n g a s o l u t i o n of 14 grams of CrCl3»6H20 i n 18 ml of water f o r
10 minutes and then s a t u r a t i n g t h e s o l u t i o n with hydrogen c h l o r i d e
a t 8**C.
The f i l t e r e d s o l u t i o n was then poured i n t o 200 ml of d i -
e t h y l e t h e r s a t u r a t e d with hydrogen c h l o r i d e a t 10**C.
The s o l u t i o n
was thoroughly mixed while p a s s i n g hydrogen c h l o r i d e through i t ,
and was then allowed t o s t a n d f o r s e v e r a l hours a t 10®C.
The p r o -
duct was washed with d i e t h y l e t h e r s a t u r a t e d with hydrogen c h l o r i d e
and was d r i e d over c o n c e n t r a t e d s u l f u r i c a c i d i n a d e s i c c a t o r .
The Hexamethylenetetramine Metal Complexes
A l l of t h e hydrated hexamethylenetetramine metal compounds were
p r e p a r e d by the same g e n e r a l technique used by e a r l i e r i n v e s t i g a t o r s
(3-5).
Ten grams of t h e a p p r o p r i a t e metal s a l t was d i s s o l v e d i n 10
ml of w a t e r ; t o t h i s s o l u t i o n was added a s o l u t i o n of 20 grams of
hexamethylenetetramine (HMTA) in 30 ml of w a t e r .
The r e s u l t i n g p r e -
c i p i t a t e was washed with a small amount of w a t e r , then a c e t o n e , and
f i n a l l y d i e t h y l e t h e r , and allowed t o dry t o ambient t e m p e r a t u r e s .
For t h e Co(HMTA)2Cl2*10H20 and Co(HMTA3^Br2'10H20 complexes i t was
n e c e s s a r y t o keep drying times t o a minimum, s i n c e they r e a d i l y l o s t
water of h y d r a t i o n when exposed t o t h e atmosphere f o r extended p e r i ods of t i m e .
A l l samples were s t o r e d i n s e a l e d c o n t a i n e r s
after
drying t o prevent dehydration from o c c u r r i n g .
In t h e p r e p a r a t i o n of the n i c k e l bromide and n i c k e l i o d i d e comp l e x e s , n i c k e l carbonate was used as t h e s t a r t i n g m a t e r i a l .
Ten
grams of NiC03 was d i s s o l v e d i n a minimum amount of hydrobromic o r
h y d r o i o d i c a c i d and t h e s o l u t i o n of HMTA was added as b e f o r e .
The mercuric c h l o r i d e complex was prepared by g r i n d i n g a s l u r ry of HgCl2, HMTA, and a s m a l l amount of w a t e r .
l u t e d and t h e i n s o l u b l e r e s i d u e f i l t e r e d off.
The s l u r r y was d i The HMTA complex was
then p r e c i p i t a t e d with acetone and r e c r y s t a l l i z e d from acetone and
water.
The anhydrous compounds (except f o r t h o s e contedning n i t r a t e
and s u l f a t e a n i o n s ) were o b t a i n e d by h e a t i n g t h e h y d r a t e d compounds
a t 100**C f o r one h o u r .
Since h e a t i n g t h e n i t r a t e and s u l f a t e com-
pounds a t t h i s temperature caused c o n s i d e r a b l e o x i d a t i o n , i t was n e c e s s a r y t o dehydrate t h e s e complexes a t 70^C in vacuo.
After 24 hours
dehydration was complete and t h e r e was no evidence of decomposition
of t h e complex.
Methods of Analysis
Analysis of Chromium in the Chromium(III) Chloride 6-Hydrates
Chromium i n t h e isomeric chromium(III) c h l o r i d e 6-hydrates was
analyzed by o x i d a t i o n of chromium(III) t o chromate, followed by p r e c i p i t a t i o n with barium c h l o r i d e .
A weighed sample of t h e complexes
was d i s s o l v e d i n d i s t i l l e d water and s u f f i c i e n t 30 p e r c e n t hydrogen
peroxide was added t o oxidize t h e chromium(III) t o chromate.
An e x -
cess of a 1 N s o l u t i o n of barium c h l o r i d e was added, and t h e p r e c i p i t a t e was f i l t e r e d off,
d r i e d a t 110°C, and weighed as BaCrOi*.
Analysis of Metal Content i n Hexamethylenetetramine Complexes
The metal ion c o n t e n t s of t h e complexes used i n t h i s study were
determined by i g n i t i o n of the compounds t o t h e metal o x i d e s .
A
weighed sample of t h e compound was p l a c e d i n a t a r e d c r u c i b l e and
h e a t e d with a Bunsen b u r n e r flame u n t i l the i n i t i a l c h a r r i n g of t h e
complex was completed.
This was followed by f u r t h e r i g n i t i o n of t h e
c o n t e n t s i n a muffle furnace a t 700°C f o r a p e r i o d of one hourAnalysis of Chloride i n t h e Chromium(III) Chloride 6-Hydrates
The chromium(III) c h l o r i d e 6-hydrates were analyzed f o r both
i o n i z a b l e and t o t a l c h l o r i d e c o n t e n t .
The amount of i o n i z a b l e c h l o -
r i d e was determined by the addition of an excess of a cold s i l v e r
n i t r a t e solution t o a solution of the complexes dissolved in d i s t i l led water maintained at 0®C.
The r e s u l t i n g solution was thoroughly
mixed and immediately f i l t e r e d .
The s i l v e r chloride p r e c i p i t a t e was
washed with d i s t i l l e d water, d r i e d , and weighed.
Total chloride con-
t e n t was determined by adding an excess amount of s i l v e r n i t r a t e t o
a solution of the complex and b o i l i n g for 15 minutes.
The solution
was then cooled and the s i l v e r chloride f i l t e r e d off, dried at 110**C,
and weighed.
Analysis for Halide Ions in Hexamethylenetetramine Complexes
The hexamethylenetetramine complexes were analyzed for halide
content by t i t r a t i o n with a standardized solution of s i l v e r n i t r a t e
a f t e r complete i g n i t i o n of the complexes in a ShCniger oxidation
flask.
Sample sizes of 40 to 50 mg were used.
carried out with a 5 ml
raicro-buret,
The t i t r a t i o n s were
using potassium chromate as the
indicator.
Analysis for Nitrogen
All nitrogen determinations were made on a Coleman Model 29 Nitrogen Analyzer.
This instrument i s an automated micro-Dumas appara-
tus which determines nitrogen content in materials which w i l l d i s s o c i a t e at temperatures below 1100°C.
Sample s i z e s of approximately 4 mg were weighed out i n t o small
aluminum b o a t s .
These were placed in the quartz combustion tube
which was then packed with cupric oxide.
The temperature of the two
combustion furnaces was s e t a t 850^0 and t h e p o s t h e a t e r temperature
was 550®C.
The i n s t r u m e n t ' s automatic combustion cycle was used with
an a d d i t i o n a l two minute time delay during f i n a l combustion t o i n s u r e
con5>lete decomposition.
After a l l o t h e r gases were absorbed by t h e
potassium hydroxide s o l u t i o n i n t h e n i t r o m e t e r , t h e volume of n i t r o gen evolved was read from a d i g i t a l r e a d - o u t d i a l which was l i n k e d by
a micrometer screw t o the m i c r o - s y r i n g e .
I n s t r u m e n t a l Methods
Thermogravimetric Analysis Studies in Air
The thermogravimetric a n a l y s i s (TGA) s t u d i e s i n a i r were made
on an automatic r e c o r d i n g thermobalance which has p r e v i o u s l y been
described(6).
Sample s i z e s of approximately 70 mg were used.
Unless
otherwise s p e c i f i e d , a furnace h e a t i n g r a t e of 5 degrees p e r minute
was employed.
Thermogravimetric Analysis Studies in Vacuo
An Ainsworth semi-micro vacuum r e c o r d i n g balance equipped with
a furnace and temperatiu?e programmer as p r e v i o u s l y d e s c r i b e d ( 7 ) was
employed.
Sample s i z e s ranged i n weight from 8 t o 20 mg.
The sam-
p l e s were pyrolyzed u s i n g a furnace h e a t i n g r a t e of 2.5**C p e r minute
and a t a p r e s s u r e of approximately 0.020 t o r r .
The same i n s t r u m e n t was used t o determine completeness of r e a c t i o n f o r sample p r e p a r a t i o n s in vacuo,
A s p e c i a l Nichrome c o n t a i n -
e r of approximately 1 gram c a p a c i t y was employed t o hold t h e sample.
A t o t a l weight l o s s of 400 mg f o r p y r o l y t i c p r e p a r a t i o n s could be
8
followed c o n t i n u o u s l y .
The sample was heated t o t h e d e s i r e d tempera-
t u r e and maintained a t t h a t temperature u n t i l t h e d e s i r e d weight l o s s
was observed.
D i f f e r e n t i a l Thermal Analysis and Gas Evolution Studies
The d i f f e r e n t i a l thermal a n a l y s i s (DTA) and gas e v o l u t i o n (GE)
apparatus used has been d e s c r i b e d p r e v i o u s l y ( 8 ) .
The samples ranged
i n weight from 50 t o 75 mg and were decon^josed i n a djrnamic helium
gas atmosphere.
The presence of evolved decomposition gases i n t h e
helium gas stream was d e t e c t e d by a t h e r m i s t o r thermal c o n d u c t i v i t y
detector.
Output s i g n a l s from t h e DTA a m p l i f i e r and GE d e t e c t o r
were recorded as a function of temperature on two X-Y r e c o r d e r s .
furnace h e a t i n g r a t e of 10°C p e r minute was employed.
A
Previously
i g n i t e d alumina was used as t h e r e f e r e n c e m a t e r i a l .
Reflectance and Dynamic Reflectance Spectroscopy S t u d i e s
High temperature r e f l e c t a n c e measurements were made using a
heated sample h o l d e r ( 9 , 1 0 ) a t t a c h e d t o a Beckroan Model DK-2A s p e c troreflectometer.
Samples were s t u d i e d alone as w e l l as i n a m a t r i x
of v a r i o u s m a t e r i a l s .
When a m a t r i x m a t e r i a l was employed, a r a t i o
of one p a r t complex t o nine p a r t s m a t r i x by weight was used.
Meas-
urements were made i n t h e 350-750 my range u s i n g magnesium oxide as
the reference material.
In g e n e r a l , samples were heated a t a r a t e
of two degrees C p e r minute.
X-Ray D i f f r a c t i o n
Studies
The X-ray d i f f r a c t i o n p a t t e r n s were t a k e n on a Norelco D i f f r a c -
tometer manufactured by P h i l l i p s E l e c t r o n i c s , Inc.
The r a d i a t i o n
was a N i - f i l t e r e d Cu Ka radiation obtained using 30 KV electrons a t
a current of 15 mA.
The isomeric chromium(III) chloride 6-hydrates were heated gent l y with a flame u n t i l the i n i t i a l decomposition and frothing had
subsided and then ignited in a muffle furnace at 500°C for 24 hours.
The samples were thoroughly ground and r e i g n i t e d for an additional
2 hours.
The samples were ground again and placed in the sample hold-
e r of the X-ray u n i t .
The i n t e n s i t y of the s c a t t e r e d X-ray radiation
was p l o t t e d against s c a t t e r i n g angle in degrees of 2G on a s t r i p
chart recorder.
Magnetic Susceptibility Studies
The magnetic moments of the complexes were determined by the
Gouy method.
The apparatus used was a modification of the high tem-
perature apparatus previously d e s c r i b e d ( l l ) .
I t consisted of a Sar-
t o r i u s single pan balance. Model No. 2503, an Atomic Laboratories
aluminum foil-wound electromagnet, and a d . c . 0-10 amp magnet power
supply.
The sample container was a Pyrex glass t u b e , 6 mm in diame-
t e r and 10.2 cm in length, sealed at one end.
The tube was marked
5.5 cm from the bottom so t h a t the sample could be consistently
packed t o the same h e i g h t .
The packed tube was then placed so t h a t
the bottom of the tube extended half the way down between the magnet
pole p i e c e s .
The tube and contents were weighed with the current off
and then reweighed a f t e r adjusting the magnetic f i e l d strength t o
about 8.000 gauss.
10
Copper s u l f a t e 5-hydrate was used as the s t a n d a r d for t h e d e t e r mination of 3 , t h e tube c a l i b r a t i o n c o n s t a n t .
The mass magnetic s u s -
c e p t i b i l i t y (x) of CuS0^»5H20 has been determined t o be 5.92 x 10"^
cgs.units(12).
The mass s u s c e p t i b i l i t y of t h e complexes i s given by t h e equation:
"^
m
where a i s a c o n s t a n t allowing f o r the displacement of a i r by t h e
sample and e q u a l t o 0.029 x specimen volume, 3 i s t h e tube c a l i b r a t i o n c o n s t a n t , m i s t h e mass of t h e specimen, F i s t h e observed
change i n weight of the sample, and 6 i s t h e change i n weight of t h e
empty sample t u b e .
The c o r r e c t e d molar s u s c e p t i b i l i t y i s t h e n :
5,.
X 106 =
^ m '^ -^^
^X ^ C)
MW
where MW is the molecular weight of the complex and C is the diamagnetic correction for the ligands. All diamagnetic corrections were
taken from the values listed by Figgis and Lewis(13). The magnetic
moment, u ^- , is then given by the following equation:
err.
u -err.
=
2.84 (x* T)^/^ Bohr Magnetons
m
where T is the temperature in degrees Kelvin.
Calorimetric Studies
All h e a t s of r e a c t i o n were determined on a Perkin-Elmer Model
DSC-1 D i f f e r e n t i a l Scanning C a l o r i m e t e r which has been p r e v i o u s l y
described(14,15).
Samples r a n g i n g i n weight from 5 t o 14 mg were
11
c o n t a i n e d i n small aluminum cups.
The loaded sample cup was p l a c e d
i n t o t h e sample h o l d e r c a v i t y of t h e c a l o r i m e t e r and an empty cup
placed in the reference cavity.
The c a l o r i m e t e r cover was then locked
i n t o p l a c e and t h e h e a t i n g cycle s t a r t e d .
The h e a t i n g r a t e , i n s t r u -
ment r a n g e , and s t r i p - c h a r t r e c o r d e r speed were a l l v a r i e d t o o b t a i n
r e a c t i o n peaks of optimum a r e a f o r measurement.
Areas of t h e DSC
curves were determined by means of a p l a n i m e t e r .
The h e a t of fusion of t i n , 14.5 c a l o r i e s p e r gram, was used as
t h e s t a n d a r d f o r t h e d e t e r m i n a t i o n of the sample h e a t s of r e a c t i o n .
Standard a r e a s were determined under t h e same i n s t r u m e n t a l s e t t i n g s
as t h o s e used f o r each of t h e sample r\ins.
Hydrogen Chloride Evolution Studies
A schematic diagram of the hydrogen c h l o r i d e e v o l u t i o n apparatus
i s shown i n Figure 1.
The p y r o l y s i s chamber c o n s i s t e d of a Vycor
g l a s s t u b e , 20 mm i n diameter and 15 cm i n l e n g t h , which was f i t t e d
with a Nichrome wire-wound f u r n a c e .
The chamber was continuously
flushed with a stream of n i t r o g e n g a s .
The p y r o l y s i s products of h y -
drogen c h l o r i d e and w a t e r were passed i n t o a b u b b l e r tube and d i s p e r s e d as very s m a l l bubbles i n an aqueous s o l u t i o n which was s t i r r e d
continuously by a magnetic s t i r r e r t o i n s u r e complete a b s o r p t i o n of
the gases.
The changes i n pH of t h i s s o l u t i o n were measured with a
Beckman Zeromatic pH meter whose o u t p u t was recorded on t h e Y a x i s
of an X-Y r e c o r d e r .
The output from a Chromel-Alumel thermocouple,
which was used t o determine sample temperature i n t h e p y r o l y s i s chamb e r , was recorded on t h e X a x i s of t h e r e c o r d e r .
12
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Samples of approximately 130 mg were heated a t a r a t e of 2.5 d e grees p e r minute.
The flow r a t e of t h e gas was maintained between 50
and 60 ml p e r minute.
The pH of t h e s o l u t i o n was i n i t i a l l y s e t a t
approximately 3.5 with n i t r i c a c i d t o keep t h e pH change t o 2 u n i t s .
As a check on the hydrogen c h l o r i d e c o n c e n t r a t i o n , t h e s o l u t i o n was
analyzed f o r c h l o r i d e c o n t e n t a t t h e end of each r u n .
Thermal I n f r a r e d Spectroscopy Studies
The high temperature i n f r a r e d t r a n s r a i t t a n c e s p e c t r a , from 2.5 y
t o 16 y, were obtained u s i n g h e a t e d sample and r e f e r e n c e h o l d e r s a t t a c h e d t o a Perkin-Elmer Model 237 I n f r a r e d Spectrophotometer.
A
schematic diagram of t h e sample and r e f e r e n c e h o l d e r s i s shown i n
Figure 2 .
The h o l d e r s c o n s i s t e d of Pyrex g l a s s t u b e s , 18 mm i n d i -
ameter and 5 cm i n l e n g t h , which were f i t t e d with s m a l l Nichrome
wire-wound f u r n a c e s .
Pyrex g l a s s s l e e v e s , 15 mm i n diameter and 2 . 3
cm i n l e n g t h , were i n s e r t e d i n t o t h e furnace tube t o hold t h e KBr
p e l l e t s p e r p e n d i c u l a r t o the beam of t h e spectrophotometer-
The
sample h o l d e r contained a Chromel-Alumel thermocouple t o determine
t h e t e m p e r a t u r e a t the c e n t e r of the sample KBr p e l l e t .
t u r e was v a r i e d by manual adjustment of t h e power s u p p l y .
The temperaThe two
furnaces were connected i n s e r i e s from the same power supply t o e l i minate change i n t h e s p e c t r a due t o blackbody r a d i a t i o n from t h e
furnace.
Since many t y p e s of decomposition r e a c t i o n s are n o t d e t e c t a b l e
when t h e sample i s p r e s s e d d i r e c t l y w i t h i n the KBr p e l l e t , an a l t e r n a t e procedure was used.
Approximately 1 mg of compound was rubbed
14
Ho a t e d SamTDle H o l d e r
_-_-J
f
•"^w...
Infrared
Spectrophotometer
i
:]^
W
rcoioronce
^
3 earn
P-owsr
Supply-
Figure 2,
Thermal Infrared Spoctroscopy Apparatus
15
onto the surface of a previously prepared pure KBr p e l l e t , and the
p e l l e t was pressed again for 10 minutes at a pressure in excess of
90,000 I b . / i n . ^ .
With the compound on the surface of the p e l l e t ,
evolution of gaseous products was rapid, and the KBr matrix did
not seem t o a l t e r the r e a c t i o n .
CHAPTER III
THE THERMAL DECOMPOSITION OF THE
CHROMIUM(III) CHLORIDE HEXAHYDRATES
Review of the L i t e r a t u r e
Early i n v e s t i g a t i o n s on t h e decomposition of t h e hydrated
chromium(III) c h l o r i d e s were l i m i t e d t o the a n a l y s i s of t h e r e s i d u a l
p r o d u c t s a f t e r h e a t i n g t h e complexes a t a given t e m p e r a t u r e .
In 1845,
Moberg(16) r e p o r t e d o b t a i n i n g Cr203»8CrCl3»24H20 by h e a t i n g t h e mixed
s a l t , CrCl3»6H20, t o 120^0.
At t h e h i g h e r temperature of 150^0, he
obtained a mixture corresponding t o t h e formula, Cr203»4CrCl3»9H20.
S c h i f f ( 1 7 ) , i n 1862, r e p e a t e d Moberg's work and r e p o r t e d o b t a i n i n g
Cr2Cl5(0H)«4H20 and Cr2Cl^(0H)2'2H20 a t 120® and 150^0, r e s p e c t i v e l y .
0 1 i e ( 1 8 ) , i n 1907, r e p o r t e d t h a t [Cr(H20)^Cl2]Cl•2H20 l o s t
more than four waters when heated f o r 6 hours a t lOO^C.
slightly
The product
was dark v i o l e t i n c o l o r , h y g r o s c o p i c , and formed s o l u t i o n s i d e n t i c a l i n appearance and b e h a v i o r with the o r i g i n a l green s a l t .
Some
hydrogen c h l o r i d e , however, was l o s t under t h e s e c o n d i t i o n s .
The f i r s t q u a n t i t a t i v e i n v e s t i g a t i o n was made i n 1959 by
C u e i l l e r o n and Hartmanshenn(19); t h e two i s o m e r s , [Cr(H20)6]Cl3 and
[Cr(H20)i^Cl2]Cl»2H20, were s t u d i e d by vacuum TGA.
The i n v e s t i g a t o r s
r e p o r t e d t h a t meaningful curves could be o b t a i n e d only with slow
h e a t i n g r a t e s due t o the slow r a t e of d e h y d r a t i o n .
composition f o r t h e two isomers was r e p o r t e d t o b e :
16
The mode of d e -
17
[Cr(H20)i»Cl2]Cl-2H20
CCr(H20)6]Cl3
>
CCr(H20)^Cl2]
^
CrOo.5Cl2
> CrCl20H
>
>
> CrOCl
CrCl3«1.5H20
Cr203
> Cr203.
K i r a l y , Z a l a t n a i , and Beck(20) s t u d i e d t h e t h r e e isomers by TGA
1
i n both an a i r atmosphere and in vacuo.
They r e p o r t e d e x c e l l e n t r e -
s u l t s using a r a t h e r f a s t h e a t i n g r a t e of 10°C p e r minute.
From
t h e i r d a t a they proposed t h e following d i s s o c i a t i o n s t e p s :
CCr(H20)6]Cl3
> CrCl3-H20
CCr(H20)5Cl]Cl2'H20
[Cr(H20)^Cl23Cl«2H20
>
> Cr(0H)Cl2
>
[Cr(H20)5Cl]Cl2
>
CrOCl
>
> CrOCl
^> Cr(0H)Cl2
CCr(H20)^Cl2]Cl•H20
CCr(H20)^Cl2](0H)
> Cr(0H)Cl2
>
CrOCl.
18
Experimental Results
Analytical Results
The r e s u l t s of the a n a l y t i c a l determinations on the isomeric
complexes are shown in Table I .
Accurate determination of the ion-
izable chloride content for [Cr(H20)5Cl]Cl»H20 was not possible b e cause of i t s rapid r a t e of isomerization in s o l u t i o n .
Thermogravimetric Studies in Air
The weight-loss curves for the complexes in a i r , at a heating
r a t e of 5°C per minute, are shown in Figure 3 .
The curve for [Cr(H20)i4Cl2]Cl»2H20 showed t h a t the sample l o s t
weight beginning at 85®C and continuing u n t i l decomposition was completed at 450°C.
and 235®C.
Inflection points in the curve occurred at 155°, 180®,
The weight-loss curves for [Cr(H20)5Cl]Cl2*H20 and
CCr(H20)g]Cl3 were almost i d e n t i c a l t o t h a t of the above complex
except t h a t there was no indication of an i n f l e c t i o n point a t 180°C.
The weight-loss curves for the same complexes in a i r , but at a
heating r a t e of 2.5<*C per minute, are shown in Figure 4.
Again, the weight-loss curves for the three isomers were a l most i d e n t i c a l , but a t t h i s heating r a t e there were d e f i n i t e i n f l e c tion points in the curves at 180°C.
The hexaquochromium(III) chlo-
r i d e s t a r t e d losing weight at 85**C and continued losing weight at a
decreasing r a t e u n t i l 155^*0 (point a) was a t t a i n e d where decomposition again became quite r a p i d .
The decomposition reaction slowed up
abruptly at 195®C (point b) and then increased again slowly u n t i l i t
19
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20
[cr(H2C)5]ci^
A.
5
— [cr(H20)i^Cl^Cl«2K20
l i e a t i n s Rate - 5.0 °C/min.
CO
CO
c:5
w
20^
100
L-
200
300
L" rriT'"^''"!
Figure 5«
"^^ Curves, Air-Atmosphere
I;
500
21
[cr(H20)^]ci^
B
[cr(H20)[^Cl2]ci*2H20
C
rar(H20)5Cl]ci2*H20
Heating Rate = 2 . 5 °C/min.
CO
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'C5
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100
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i
TSIviPERATURS
F i g u r e i;,
TGA C u r v e s ,
Air-Atmosphere
_ll
22
was completed a t 400°C (point c ) .
Calculations from the weight-loss curve indicated t h a t the
i n i t i a l weight loss t o point (a) represented the loss of a species
having an atomic mass of approximately 79 t o 85.
The weight loss
from point (a) t o point (b) represented the loss of an additional
33 t o 38 a.m.u. and from point (b) to point (c) another 72 to 79
a.m.u.
The t o t a l weight loss represented 72.5% of the t o t a l sample
weight.
The complex, [Cr(H20)^Cl2]Cl•2H20, began to decompose at 90^0;
weight loss continued with a decreasing r a t e u n t i l 165°C, point (a)
on the curve.
This weight loss amounted t o approximately 71 a.m.u.
The r a t e of decomposition increased sharply between 165^0 and 220<*C
(point b ) ; the loss was equivalent to about 39 a.m.u.
The f i n a l step
in the decomposition corresponded t o approximately 79 a.m.u.
The
t o t a l weight loss represented 73.9% of the t o t a l sample weight.
The decomposition of [Cr(H20)5Cl]Cl2*H20 s t a r t e d at 60^0, a
s l i g h t l y lower tenperature than the other two complexes.
The i n f l e c -
tion points were at 195**C (point a) and 210°C (point b ) , with completion of the reaction occurring a t 410®C.
The three decomposition
steps corresponded t o the successive loss of 78, 35, and 77 a.m.u.
The t o t a l weight loss represented 71.8% of the t o t a l sample weight.
Thermogravimetric Studies in Vacuo
The weight-loss curves, in vacuo, for the chromium(III) chlor i d e 6-hydrates are shown in Figure 5.
As indicated by the curve
for [Cr(H20)6 3Cl3, there was no i n i t i a l weight loss at ambient tem-
23
[cr(H20)5]ci^
[cr:H20)^Cl]ci2-H20
[cr(H20)!^Cl2]G1^2H2^
TE.v:r^.;ATURS
Figure 5^
"C
TGA Curves, in Vacu •o
24
p e r a t u r e s a t a p r e s s u r e of 0.02 t o r r .
The complex s t a r t e d l o s i n g
weight a t 50^C; t h i s weight l o s s was continuous u n t i l decomposition
was completed a t SOO^'C.
The t o t a l weight l o s s corresponded t o 71.2%
of t h e i n i t i a l sample w e i g h t .
The TGA curve f o r [Cr(H20)5Cl]Cl2-H20 showed an i n i t i a l l o s s a t
ambient t e m p e r a t u r e s corresponding t o the l o s s of one mole of water
p e r mole of complex.
The complex s t a r t e d l o s i n g weight again when
t h e t e m p e r a t u r e reached 45<>C and continued t o l o s e weight u n t i l t h e
decomposition r e a c t i o n was completed a t 500°C.
The t o t a l weight l o s s
corresponded t o 70.7% of the o r i g i n a l sample weight.
The curve f o r CCr(H20)^Cl2]Cl-2H20 a l s o showed an i n i t i a l weight
l o s s a t ambient temperatures which was e q u i v a l e n t t o two moles of
water p e r mole of complex.
As b e f o r e , weight l o s s was continuous un-
t i l decomposition was complete.
The t o t a l weight l o s s corresponded
t o 70.4% of t h e o r i g i n a l sample w e i g h t .
X-Ray S t u d i e s
To determine the i d e n t i t y of t h e p y r o l y s i s product of t h e comp l e x e s , an X-ray d i f f r a c t i o n p a t t e r n of t h e product was t a k e n , and
t h e r e s u l t s a r e given i n Table I I .
D i f f e r e n t i a l Thermal Analysis and Gas Evolution S t u d i e s
The d i f f e r e n t i a l thermal a n a l y s i s (DTA) and gas e v o l u t i o n (GE)
curves for t h e t h r e e chromium(III) c h l o r i d e 6 - h y d r a t e s a r e shown i n
F i g u r e s 6 , 7, and 8.
The DTA curves showed two endothermic r e a c t i o n s
f o r each complex, t h e f i r s t r e a c t i o n o c c u r r i n g between 95° and 100°C
and t h e second between 155** and 170**C.
At t e m p e r a t u r e s above 200®C,
25
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o
CO
•r-l
CO
C3
o
; - i
(—
CO
K
c
^
rH
fr:
fn
PH
a>
X
i^c:
/•
^
w
tH
EH
rH
Cij
•r-t
•
^
c-
^*
o
u
o
C_'
<M
Q
CT'
%H
iSi:ods.-.H
29
t h e decomposition r e a c t i o n s involved such small e n t h a l p i c changes
t h a t no peaks were e v i d e n t but t h e r e was a d e v i a t i o n of t h e curves
from t h e i n i t i a l base l i n e .
The GE curves showed t h a t a l l r e a c t i o n s
involved t h e e v o l u t i o n of gaseous p r o d u c t s .
Reflectance Spectroscopy Studies
The r e f l e c t a n c e s p e c t r a of t h e t h r e e isomers i n a 90% alumina
m a t r i x were taken a t ambient and v a r i o u s e l e v a t e d temperatures and
a r e shown i n Figures 9, 10, and 1 1 .
For CCr(H20)5]Cl3, peak maxima were noted a t 415 mp and 580 mp.
Upon h e a t i n g t o 105°C, t h e maxima s h i f t e d t o 470 my and 675 my, and
upon f u r t h e r h e a t i n g , t h e a b s o r p t i o n bands ( r e f l e c t a n c e minima) vanished completely.
The curve peak maxima f o r [Cr(H20)5Cl]Cl2'H20 were found t o be
a t 440 my and 645 my, r e s p e c t i v e l y , and t h o s e f o r [Cr(H20)^Cl2]Cl2H2O were a t 445 my and 645 my, r e s p e c t i v e l y .
At both 105® and 160^0,
t h e r e f l e c t a n c e curves f o r t h e s e complexes were i d e n t i c a l t o those of
t h e hexaquocomplex a t t h e same t e m p e r a t u r e s .
Hydrogen Chloride Evolution S t u d i e s
The d a t a o b t a i n e d from t h e hydrogen c h l o r i d e e v o l u t i o n apparatus
were i n t h e form of p l o t s of the pH of t h e t e s t s o l u t i o n s versus
the
t e m p e r a t u r e of t h e p y r o l y s i s f u r n a c e ; t h e s e p l o t s are shown i n Figures
1 2 , 1 3 , and 14.
A l l t h r e e isomers showed a very r a p i d decrease i n t h e
pH a t t h e i r m e l t i n g p o i n t s and t h e r e a f t e r t h e pH decreased continuously
with only s m a l l i n f l e c t i o n s i n t h e curves u n t i l t h e decomposition was
completed.
30
WAVELENGTri
' i g u r e 9*
ReTlectance
Spoctra
31
-10
[cr(H20)
Cl]ci2'H2^
A — 25^0
WAVELENGTH, rn;a
Fi^mre 1 0 ,
•LJ'-
Reflectance
Spectra
32
[0r(K2O)|^ClJci*2H2O
-20
A — 2".^C
B — 110 C
C — i6o°c
-60
ILOO
U5O
500
550
I
WAVELENGTH, mu
Fip;are 1 1 .
Reflectance
Spectra
600
650
700
33
o
CD
c
>
o—
rCN
c.-)
r>
o
_4
v^
r.1
^ ^-'
—(
!-->
t—
• ^'
"-H
'-J
o
^
r-<
r"
rA
O
>
W
o
C\J
o
rH
9
o
o_
CM
•H
O
t
FA
LTN
o
CM
CM
X-
-1.
34
o
-:t
O
o
>
NN
CJ)
O
0
o
o
TA
O
o.
rr;
•P
H
o
>
til
rj
—^
CM
CH
o
o
o
u
>^
O
orA
rH
O
U
5
•H
-N
O
Li'N
o
N^
KN
CNJ
eg
J-
I
hd
35
o
o
CM
I---I
.
r-\
O
CM
rA
c:)
o
o
cu
KN
c;
>
JH
r-C
^
CJ)
o
C
o
G
Ti
O
CCM
w
'>-'
4^
ID
rA
H
<
O
>
cr:
t£l
:^
••
r
^i-i
H
0
w
.-1\
•"^
TH
!^.
o
r-'.
,c
c_^
c
O"!
':.0
o
CH
tj'
O
o*
'^
W
rA
•H
I
O
ITN
o
KN
CM
CM
I
Hd
36
This data becomes muc:h more meaningful when it is replotted as
moles of hydrogen chloride evolved versus
the furnace temperature,
as shown in Figures 15, 16, and 17. The veiy large initial decrease
in pH at the melting points of the complexes was equivalent to only
0.25 to 0.33 of a mole of hydrogen chloride per mole of complex. All
three complexes showed inflection points between 200® and 250®C where
the loss of the first mole of hydrogen chloride was completed. The
final two moles of hydrogen chloride were lost, without any indication of a stepwise reaction, between 250° and 400®C.
37
o
o
KN
>
0
o
o
CJ)
O
•H
4-)
O
>
O
ocu
PH
w
EH
q
r—1
CO
O
O"
to
o
.
UN
H
0
U
•H
o
CJ
I
lOK dio si^ia^VAinba
rov
38
•D
>
J^
^
C3
CJ>
o
O
*-»
r-T
.—I
-J>
• ^
r^
rH
O
>
r
w
V-<
^.^,
•-'
C-j
P-,
T:^
EH
G
'C5
^
O
rH
r-t
r*-t
o
c
<D
tjO
o
fn
^ _ j
>>
w
VD
0
to
.H
lOH ao siMaivAinoa
39
o
o"
O
CvJ
CM
.
rH
O
fvj'
rA
C3
O
O.
O
CM
<D
I*
O
o
o
r—'
>-4
o
T^
TrJI
rr:
r^
tH
'^
Cd
O
o
CM
('1
4^
::<
r-4
O
>
w
(^
'-L'
• ^ • l
•TJ
l » ^
Ci3
EH
.r^
o
r-i
r-
G
!•-<
c:;
••0
o
O
O"
H
rH
O
•up
OJ
O
1
10 K
JO s:;u9XBA-ynos
KN
40
Discussion and Conclusion
The w e i g h t - l o s s c u r v e s , i n a i r , f o r t h e chromium(III) c h l o r i d e
6 - h y d r a t e s show t h r e e important f a c t s .
F i r s t , the t e r m i n a l product
of t h e t h e r m a l d i s s o c i a t i o n r e a c t i o n i s Cr203, n o t CrOCl (a mixture
of CrCl3 and Cr203), as p r e v i o u s l y r e p o r t e d ( 1 9 , 2 0 ) .
For complete con-
v e r s i o n of t h e complexes t o Cr203, a weight l o s s of 71.48% i s r e q u i r e d
by t h e o r y .
This i s i n good agreement with t h e values obtained from
the thermogravimetric s t u d i e s .
The formation of CrOCl r e q u i r e s a
61.16% weight l o s s and t h e formation of CrOCl, with subsequent v o l a t i l i z a t i o n of t h e CrCl3 from t h e m i x t u r e , r e q u i r e s a t o t a l weight
l o s s of 80.99%.
Second, the s i m i l a r i t y of t h e curves f o r t h e t h r e e isomers i n d i c a t e d t h a t t h e compounds may involve the same i n t e r m e d i a t e s in t h e
thermal d i s s o c i a t i o n
reaction.
T h i r d , t h e mode of decomposition depends upon the h e a t i n g r a t e
employed.
This confirms C u e i l l e r o n and Hartsshenn*s
findings(19)
t h a t the r e a c t i o n i n v o l v e s c l e a r - c u t s t e p s only a t slow h e a t i n g r a t e s .
The weight l o s s curves of t h e compounds, in vacuo,
information with r e g a r d t o the r e a c t i o n i n t e r m e d i a t e s .
gave l i t t l e
The t o t a l
w e i g h t - l o s s p e r c e n t a g e s d i d , however, show t h a t t h e f i n a l product was
Cr203 and t h a t t h e thermal decomposition did not involve a i r o x i d a t i o n ,
The i n i t i a l weight l o s s of t h e two isomers with uncoordinated w a t e r s
of h y d r a t i o n i s i n e x c e l l e n t agreement with t h e r e s u l t s r e p o r t e d by
Godefroy(23).
A d d i t i o n a l confirmation r e g a r d i n g t h e composition of t h e t h e r m a l
41
dissociation residue was obtained by the X-ray studies. The residue
previously reported as CrOCl(19,20) should have contained diffraction
lines of both Cr203 and CrCls. The data indicated only the presence
of Cr203 lines while the CrCl3 lines were absent, thus the final product was Cr203.
i
The reflectance studies indicated that the same product was obtained for all three isomers after the initial reaction at lOO^C.
Since the reaction involved melting of the complexes, it is likely
that the spectra represent
an equilibrium mixture of the three orig-
inal isomers plus lower hydrate species. Such interconversion of the
pure isomers to an equilibrium mixture is well known in aqueous solution(24,25).
It is the formation of this equilibrium mixture which
accounts for all three isomers decomposing in the same manner.
Upon comparison of the weight-loss curves with the hydrogen
chloride evolution curves, it appeared that the thermal dissociation
consists of a series of successive and overlapping reactions. The
reactions involved are:
CCr(H20)6]Cl3(s)
1
CCr(H20)5Cl]Cl2'H20(s)
[Cr(H20)^Cl2]Cl-2H20
• CrCl3«6H20(l)
t
'
2CrCl3-6H20(l) — • (CrCl3)2*3H20(s)
(CrCl3)2-3H20(s) — • Cr20Cl^-2H20(s)
C^20Cl^•2H20(s)
(1)
• Cr203(s)
+
+
9H20(g)
+
4HCl(g).
All of the above intermediates are kncjwn(26).
2HCl(g)
(2)
(3)
(4)
42
Reactions (1) and (2) account for the first reaction step at
100°C.
Reaction (3) must also occur to some extent since hydrogen
chloride is evolved. At elevated temperatures, reaction (3) becomes
more prevalent and is responsible for the cicomposition at 160°C.
Above 200°C, reaction (4) is the main reaction.
CHAPTER IV
THE DEHYDRATION OF COBALT(II)
CHLORIDE AND BROMIDE HEXAHYDRATES
Review of t h e L i t e r a t u r e
Although there have been no investigations concerning the ions
present in the l i q u i d melts of c o b a l t ( I I ) chloride and bromide 6-hyd r a t e s , there have been several studies made on the formation of t e t rahedral complexes in s o l u t i o n .
Robinson and Brown(27) concluded from
spectrophotometric studies in aqueous s a l t solutions t h a t the blue
complex formed i s for the most part a dichloro-complex of cobalt.
Wormser(28), on the basis of conductivity measurements in acetone, r e ported t h a t the complex i s a trichloro-complex.
Katzin and Gebert(29) made an extensive spectrophotometric i n v e s t i g a t i o n of the effects of variation of chloride concentration and
of solvents on the formation of the t e t r a h e d r a l complexes.
The spec-
t r a of the complexes found t o e x i s t in solution a t various concentrations of chloride ions were characterized.
In agreement with the two
previous i n v e s t i g a t i o n s , Katzin and Gebert reported a s h i f t of the
equilibrium in acetone from the trichloro-complex t o the dichlorocomplex when small amounts of water were added t o the s o l u t i o n .
In
aqueous s o l u t i o n , even at high chloride concentrations, only small
amounts of the tetrachloro-complex were d e t e c t a b l e .
Katzin and Gebert(30) also investigated a number of known t e t r a hedral c o b a l t ( I I ) s o l i d s by reflectance spectroscopy.
43
They reported
44
excellent c o r r e l a t i o n of the reflectance spectra with the solution
s p e c t r a of the same complexes.
Shen and Chang(31) made an extensive investigation of the t h e r mal decomposition of c o b a l t ( I I ) chloride and bromide by TGA, DTA,
and powder X-ray diffraction techniques.
The r e s u l t s of t h e i r i n -
vestigations indicated t h a t dehydration became extensive a f t e r melting of the compounds at about 50°C.
Dehydration was reported as b e -
ing continuous u n t i l the formation of the 2-hydrate at 120°C.
There
was no indication of the formation of any stable intermediate hydrate
nor any appreciable amount of hydrolysis as a competing r e a c t i o n .
45
Experimental R e s u l t s
Reflectance Spectroscopy S t u d i e s
The r e f l e c t a n c e s p e c t r a of c o b a l t ( I I ) c h l o r i d e 6 - h y d r a t e , a t
v a r i o u s s t a g e s of dehydration i n a 90% KCl m a t r i x , are shown i n F i g ure 18.
At 50<^C, t h e 6-hydrate melted i n i t s own waters of h y d r a -
t i o n ; t h e r e f l e c t a n c e curve of t h e r e s u l t i n g s o l i d , curve A, showed
a s t r o n g band from 625 my t o 700 my and a shoulder band between 525
my and 570 my.
The melt a p p a r e n t l y contained u n s t a b l e complexes
s i n c e t h e spectrum continued t o change with t i m e .
After 15 minutes
a t 50°C, t h e spectrum of CoCl2'2H20 curve B, was o b t a i n e d .
The 2 -
h y d r a t e had decomposed by 110°C, and the f i n a l product was o b t a i n e d .
The spectrum of t h i s product (shown by curve C) was c h a r a c t e r i z e d by
a s t r o n g band between 625 my and 700 my and by small peaks a t 535 and
450 my.
I t i s e v i d e n t from t h e previous s t u d i e s d e a l i n g with complex
formation of C0CI2 i n excess KC1(32,33) and p r e v i o u s l y p u b l i s h e d r e f l e c t a n c e s p e c t r a ( 3 0 ) t h a t the f i n a l product i s K2CoCl^,
The same dehydration r e a c t i o n c a r r i e d out i n a 60% alumina mat r i x i s shown i n Figure 19.
The r e f l e c t a n c e curve o b t a i n e d a t 25°C
(curve A) showed t h e spectrum of CoCl2*6H20, which was c h a r a c t e r i z e d
by peaks a t 540 my, 500 my, and 455 my.
At SO^C, the 6-hydrate m e l t -
ed and t h e r e f l e c t a n c e curve of t h e r e s u l t i n g s o l i d (curve B) showed
a s t r o n g band from 625 my t o 700 my and a broad peak with t h e maximum a t 535 my.
The spectrum, as shown by curve C, changed very l i t t l e
o v e r a p e r i o d of one hour a t t h i s t e m p e r a t u r e .
anhydrous c o b a l t ( I I ) c h l o r i d e was o b t a i n e d .
Upon f u r t h e r h e a t i n g ,
The spectrum of C0CI2,
46
GoCl2^6H20 i n KCl
A — 50^0, 1 minute
B — 5 0 ° C , 15 m i n u t e s
C —
llO^C
^80
1^00
500
-J
-J
550
L-
WAVELENGTH, mj.
Figure 18, Reflectance Spectra
600
-J
650
1
700
47
-10
WAVELENGTH, m^
Figure 19. Reflectance Spectra
48
as shown by curve D, c o n s i s t e d of a s i n g l e broad peak with the maximum at 605 my.
The r e f l e c t a n c e spectra of the dehydration of c o b a l t ( I I ) bromide
6-hydrate i n a KBr matrix are shown in Figure 20.
The reflectance
spectrum a f t e r the melting of the 6-hYdrate at 55<>C, as shown by
curve A, c o n s i s t e d of a band from 640 my t o 750 my, shoulder peaks at
535 my, 470, and 430 my, and a small peak at 395 my.
Over a period
of one hour there was no change in the spectrum at 55®C.
At llO^C
the f i n a l product of K2CoBri» was obtained, the spectrum of which i s
shown by curve B.
The reflectance curve showed a broad band from
640 my t o 750 my and small peaks at 570, 540, 485, 470, 465, 435, 425,
and 395 my.
I t can be seen from curve C that t h i s complex was s t a b l e
as the temperature increased from 110® to 160°C.
The dehydration of CrBr2*6H20 in a 60% alumina matrix i s shown
in Figure 2 1 .
The spectrum of the 6-hydrate, shown by curve A, con-
s i s t e d of three overlapping peaks with the maxima at 550, 510, and
455 my.
The r e f l e c t a n c e curve of the melt, curve B, showed a strong
band from 640 my t o 750 my with shoulder peaks at 535 my, 475 my,
and 435 my, and a small peak at 400 my.
The f i n a l product of anhy-
drous c o b a l t ( I I ) bromide was obtained at 110®C.
Dynamic Reflectance Spectroscopy Studies
The strong absorption band in the wavelength range from 600 my
t o 750 my i s c i i a r a c t e r i s t i c of the tetrahedral c o b a l t ( I I ) structure
and i s n o n - e x i s t e n t in the spectra of c o b a l t ( I I ) complexes with o c tahedral s t r u c t u r e s .
The difference in absorbance in t h i s region
49
C — l60^G
70
1^90
14-30
500
L_
550
600
L—
1
650
700
WAVELENGTH, rcjx
Fi^nire 2 0 .
Reflectance
Spectra
CLAAb TECHNOLOGICAL CO*.*,..*-*.
LUBBOCK. TEXAS
I I r-•-> * 53 V
50
B
10
Y/AVELENGTH, mu
Figure 2 1 .
Reflectance
Spectra
51
provides an excellent method for following the t r a n s i t i o n from one
s t r u c t u r e t o the other.
Dynamic reflectance spectroscopy was used
at a wavelength of 675 my, which i s in the middle of the t e t r a h e d r a l absorbance band.
The dynamic reflectance curves (Figures 22 and 23) show the t o t a l dehydration process.
Both c o b a l t ( I I ) chloride and bromide 6-hy-
d r a t e s , regardless of the matrix, i n i t i a l l y formed t e t r a h e d r a l complexes in the melt.
The dynamic reflectance curve showed, in the
case of c o b a l t ( I I ) c h l o r i d e , t h a t these t e t r a h e d r a l complexes d i s sociate and form the l e s s absorbent ( g r e a t e r reflectance) octahedral
2-hydrate.
Upon further heating the t e t r a h e d r a l s t r u c t u r e was r e -
formed in the KCl matrix and was stable t h e r e a f t e r .
In the alumina
matrix, the 2-hydrate decomposed in successive steps to form
CoCl2»H20 and anhydrous C0CI2.
In the dehydration of CoBr2'6H20, no formation of the octahedral
2-hydrate in the KBr matrix was observed.
The t e t r a h e d r a l s t r u c t u r e
was obtained upon melting and was retained t h e r e a f t e r .
In the a l u -
mina matrix, the t e t r a h e d r a l complex decomposed a t llO^C, the f i n a l
product being anhydrous CoBr2.
52
30
<
«50 +
in
V o
A
B -
70;
Al^Oj
X=675
mu
90--
'1
75
100
_L_
TEIviPii.nA i un.
Figur-s 2 2 .
L_
150
i
On
Dynamic R e f l e c t a n c e S p e c t r o s c o p y Curves
53
10A
\
\
> 30--
B
O
o 50--
Co3r2*oK20
in
3 — Al20^
70-L
X = 675 ^^u^
h
y
90-
5P
H
100
I
125
150
•J'
L_
TEMPERATURE
'igure 25.
Dynamic Reflectance Spectroscopy Curves
54
Discussion and Conclusion
The dynamic reflectance curves clearly showed the formation of
an intermediate octahedral complex in the dehydration of CoCl2»6H20
in a KCl matrix, but no such intermediate for the corresponding b r o mide co::.plex in KBr.
Even in the alumina matrix, which does not fa-
vor complex halide formation, the t e t r a h e d r a l dehydration intermediate of CoBr2'6H20' was considerably more stable than that of CoCl2*6H20.
This i n d i c a t e s that the dehydration involved more than the simple formation of a tetrahalo-con5)lex in the l i q u i d melt.
Results obtained by Katzin and Gebert(29), using the method of
"continuous v a r i a t i o n " , indicated that several different complexes
were formed in c o b a l t ( I I ) chloride s o l u t i o n s .
Their s p e c t r a l data
«
showed the presence of the following complexes: CoCl^^", C0XCI3",
C0X2CI2, and CoXe^+, where X represents a molecule of the solvent.
The first two complexes have tetrahedral structures, the last has an
octrahedral structure, and the complex, C0X2CI2, has both forms. The
tetrahedral C0X2CI2 complex is unstable in most solvents, but in some
cases (e.g., where X is pyridine) both the octahedral and tetrahedral
forms are stable. As was also pointed out by Katzin and Gebert, in
solvents such as water, which strongly compete with chloride ions for
a coordination position, the CoCl^^" complex is present only in minor"
quantities even when the chloride ion concentration is quite high.
Although the spectra of the three tetrahedral complexes are quite
similar, the CoCl^^" has a small distinguishing peak at 450 my and
starts absorbing strongly in the ultraviolet from 400 my(30). No
55
peak at 450 my or absorption in the region of 400 my t o 350 my was
observed in the spectrum of the CoCl2'6H20 melt.
The melt did have
a peak at 550 my, i n d i c a t i v e of the octahedral 2-hydrate(29), and
very strong absorption in the 615 my t o 725 my region showing considerable t e t r a h e d r a l complex formation.
Therefore, the melt must
have contained the three complexes, Co(H20)Cl3~,
Co(H20)2Cl2, and octdhedral-CoQl2'2\{20,
tetrahedral-
in equilibrium.
The i n s t a -
b i l i t y of the t e t r a h e d r a l 2-hydrate (with respect t o the octahedral
form) caused conversion t o the s t a b l e octahedral 2-hydrate s o l i d .
The spectrum of the CoBri^^" complex has distinguishing peaks at
395, 425, 430, 465, and 475 my.
The spectrum of the CoBr2'6H20 melt
in 90% KBr showed a l l of these peaks t o be present and increasing in
i n t e n s i t y with time.
The peak at 560 my in the melt was indicative
of the octahedral 2-hydrate, but became l e s s intense with time.
The
equilibrium of the complexes in the melt was, t h e r e f o r e , s h i f t i n g in
favor of the tetrabromo-complex as dehydration occurred.
The increased s t a b i l i t y of the t e t r a h e d r a l s t r u c t u r e of
CoBr2»2H20 was probably due t o the increase in size of the halide ion
As pointed out before, the s u b s t i t u t i o n of pyridine for water in the
molecule C0X2CI2 s t a b i l i z e s the t e t r a h e d r a l form.
CHAPTER V
THE THERMAL DECOMPOSITION OF SOME HYDRATED
HEXAMETHYLENETETRAMINE METAL COMPOUNDS
Review of the Literature
The general complexing a b i l i t y of hexamethylenetetramine has
been investigated extensively.
Complexation with the s a l t s of the
a l k a l i ( 3 4 ) , a l k a l i e a r t h ( 3 4 , 3 5 ) , rare e a r t h ( 3 6 , 3 7 ) , t r a n s i t i o n ( 3 - 5 ,
35,38), and post t r a n s i t i o n ( 3 - 5 , 3 9 ) metals have a l l been reported.
These early i n v e s t i g a t i o n s were, however, limited t o the descriptions
of preparation and stoichiometry (over which there was often disagreement).
Govozdov and Erunova(40) were the f i r s t to study the dehydration
of the complexes in any d e t a i l .
They determined, in a q u a l i t a t i v e
manner, the temperature for the dehydration of a number of cobalt and
nickel complexes and used these complexes as a s e r i e s of chemical
temperature i n d i c a t o r s .
Harmelin and Duval(41) made a s i m i l a r s e r i e s of temperature i n dicators using hexamethylenetetramine complexes of cobalt and nickel
but followed the decomposition by TGA.
They reported t h a t a l l the
complexes, except Co(HMTA)2(N03)2'10H20 and Ni(HMTA)2Cl2*10H20, underwent s i n g l e - s t e p dehydration.
The cobalt n i t r a t e complex r e p o r t -
edly l o s t s i x waters of hydration between 50^ and 95°C, with the r e maining four waters being l o s t from 95<* t o 155®C.
The complex
Ni(HMTA)2Cl2*iOH20 also was reported as undergoing a two-step dehy56
57
d r a t i o n but no formula f o r t h e i n t e r m e d i a t e h y d r a t e was s u g g e s t e d .
S t r u c t u r a l d e t e r m i n a t i o n s by X-ray d i f f r a c t i o n methods have
been l i m i t e d t o complexes t h a t are not o b t a i n a b l e from n e u t r a l aqueous s o l u t i o n s .
G i u s e p p e t t i ( 4 2 , 4 3 ) made s t u d i e s on t h e s t r u c t u r e of
hexamethylenetetramine complexes of c o b a l t ( I I ) c h l o r i d e , z i n c c h l o r i d e , and c o p p e r ( I I ) s u l f a t e .
In a l l t h r e e cases t h e c r y s t a l s were
p r e p a r e d from a very a c i d i c s o l u t i o n and t h e r e s u l t i n g compounds were
2CoCl2*4HMTA»4HCl-5H20, 2ZnCl2*4HMTA«4HCl«5H20, and CuS0^•HMTA•H2S0^.
Tang and S t u r d i v a n t ( 4 4 ) determined the c r y s t a l s t r u c t u r e of
Mn(HMTA)2Cl2*2H20.
trans
The r e s u l t s i n d i c a t e d an o c t a h e d r a l s t r u c t u r e with
arrangement of each s u b s t i t u e n t p a i r .
The s i n g l e c r y s t a l s were
grown from a 1:1 molar mixture of a l c o h o l and a c e t o n e .
The waters of
h y d r a t i o n were r e p o r t e d l y absorbed from atmospheric m o i s t u r e .
The
p r e p a r a t i o n of t h i s compound has not been r e p o r t e d from aqueous s o l u tion.
58
Experimental R e s u l t s
Analytical Results
The r e s u l t s of t h e a n a l y t i c a l d e t e r m i n a t i o n s of t h e various meta l complexes of hexamethylenetetramine t h a t were s t u d i e d are shown i n
Tables I I I and IV.
Thermogravimetric S t u d i e s i n Air
The TGA curves f o r t h e c o b a l t ( I I ) complexes, i n a i r , are shown
i n Figure 24.
The curve f o r Co(HMTA)2Cl2*10H20 showed a weight l o s s beginning
a t 40°C and ending a t 130®C, from p o i n t ( a ) t o p o i n t (b) on t h e c u r v e .
This l o s s corresponded t o 30•8% of t h e i n i t i a l sample w e i g h t , or a p proximately 182 a . m . u . , and was i n good agreement with t h e l o s s of
t h e t e n w a t e r s of h y d r a t i o n ,
Deconposition of t h e anhydrous con^jound
began a t 200^0 and became very r a p i d up t o 225®C, a t which p o i n t t h e
r a t e of decomposition again became very slow.
The r a t e of t h e d e -
composition r e a c t i o n remained slow up t o 400®C where i t again i n c r e a s e d
u n t i l decomposition was completed a t 580°C.
The r a p i d weight l o s s from
p o i n t s ( b ) t o ( c ) on t h e curve was e q u i v a l e n t t o the l o s s of a p p r o x i mately 18.1% of t h e sample weight o r 106 a.m.u.
were l o s t slowly between p o i n t s ( c ) and ( d ) .
An a d d i t i o n a l 35 a.m.u.
The f i n a l r e s i d u e c o r -
responded t o 12.5% of t h e o r i g i n a l sample w e i g h t , which was i n e x c e l l e n t agreement with t h e 12.62% c a l c u l a t e d f o r t h e f i n a l product of
CoaOij.
The TGA curves of Co(HMTA)2Br2'10H20 and Co(HMTA)2l2'10H20 were
59
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61
Co(HiVlTA)2Gl2-10H20
Co(IIlv:TA)23r2'10H20
Co(HMTA)2l2'10K20
Co(KMTA)2(NO5)2*IOK2O
Co(HiMTA)2S0|^^10H20
T2:VIFERKTURS
F i g u r e 2l|..
-O
TCIA C u r v e s , A i r - A t m o s p h e r e
62
i d e n t i c a l t o t h a t of t h e previous complex with t h e exception of t h e
f i n a l o x i d a t i o n s t e p of t h e i o d i d e compound, which was much more r a p i d
and was completed by *+90°C.
The TGA curve of Co(HMTA)2S0^•10H20 showed t h a t dehydration of
t h i s complex began a t a s l i g h t l y h i g h e r temperature than the c o r responding h a l i d e complexes.
The dehydration r e a c t i o n began a t 70®C
and was completed by 130®C, but t h e r e was only an i n f l e c t i o n in t h e
curve a t t h i s p o i n t .
Decomposition continued without meaningful
breaks in t h e curve u n t i l the f i n a l product was obtained a t 510°C.
The r e s i d u e was again Co30i^ s i n c e i t s weight correspcmded t o 13.2%
of t h e o r i g i n a l sample w e i g h t ; 13.01% i s t h e c a l c u l a t e d value for t h e
formation of CosO^.
The TGA curve of Co(HMTA)2(N03)2'10H20 showed t h a t dehydration
began a t 50®C and was q u i t e slow-
At 200OC ( p o i n t b ) , approximately
t h e p o i n t where dehydration was completed, the r e a c t i o n became very
r a p i d with a l o s s of approximately 38% of t h e sample weight i n a t e n
degree r a n g e .
From 210° t o 380°C, decomposition occurred in two s t e p s ,
but no meaningful s t o i c h i o m e t r y could be assigned t o t h e two p l a t e a u s .
The r e s i d u e corresponded t o 12.8% of t h e o r i g i n a l sample w e i g h t , 12.**^*%
being r e q u i r e d f o r t h e formation of Co30^.
The w e i g h t - l o s s curves of t h e n i c k e l complexes are shown in
Figure 2 5 .
The curve of Ni(HMTA)2Cl2'10H20 showed t h a t dehydration
o c c u r r e d between 60® and 185*0, p o i n t s ( a ) and (b) on t h e c u r v e .
An
i n f l e c t i o n p o i n t i n t h e curve a t 150°C i n d i c a t e d t h a t t h e dehydration
r e a c t i o n o c c u r r e d i n two s t e p s with approximately 130 a.m.u. b e i n g
l o s t i n t h e f i r s t s t e p and 52 a.m.u. i n t h e second dehydration s t e p .
63
A
Hi(HMTA)2Br2*10H20
B
Ni(HMTA)2Cl2'10H20
C
lNi(HI.ITA)2l2»10H20
D
Ni(HMTA)2S0j, •10K2^
00
o
EH
tn
O
M
W
2 Oc^
0^
L_
100
200
5°
1^00
L-.
^00
TEMPERATURE
Figure 25.
TGA C u r v e s , A i r - A t m o s p h e r e
600
64
The anhydrous complex s t a r t e d decomposing a t 220^0 with t h e r a p i d l o s s
of approximately 103 a.m.u. between p o i n t s (b) and ( c ) on t h e w e i g h t loss curve.
( c ) and ( d ) .
An a d d i t i o n a l 42 a.m.u. were l o s t slowly between p o i n t s
Air o x i d a t i o n began a t t h i s p o i n t and t h e f i n a l product
was o b t a i n e d a t 580<*C.
The t o t a l weight l o s s corresponded t o 87.8%
of t h e o r i g i n a l sample weight with 87.29% being r e q u i r e d f o r t h e format i o n of NiO.
The TGA curves of t h e n i c k e l bromide and iodide complexes were
very s i m i l a r t o t h a t of t h e c h l o r i d e except t h e r e was no evidence of
an i n t e r m e d i a t e h y d r a t e forming during d e h y d r a t i o n .
The TGA curve of Ni(HMTA)2SOit»10H20 showed t h a t dehydration was
immediately followed by deconposition of t h e anhydrous compound.
The
d e c o n p o s i t i o n r e a c t i o n was continuous and without meaningful s t e p s u n t i l completion of t h e r e a c t i o n a t 490*0.
The t o t a l weight l o s s was
88.2% of t h e o r i g i n a l sample w e i g h t , 87.80% being r e q u i r e d f o r t h e
formation of NiO.
The TGA curves f o r t h e remaining a d d i t i o n complexes of hexamethyle n e t e t r a m i n e t h a t were s t u d i e d are shown i n Figure 26.
The curve f o r
Mn(HMTA)2Cl2*10H20 showed t h e l o s s of 30.4% of t h e t o t a l weight of
t h e sample between 50* and 130*C, corresponding t o t h e l o s s of a l l ten
w a t e r s of h y d r a t i o n .
Decomposition of t h e anhydrous compound began
a t 180*C and continued u n t i l t h e f i n a l product was obtained a t 730*C.
The i n i t i a l decomposition of t h e anhydrous compound, between p o i n t s
( b ) and ( c ) on t h e c u r v e , was e q u i v a l e n t t o 40.5% of t h e o r i g i n a l
sample weight or approximately 200 a.m.u.
The decomposition between
p o i n t s ( c ) and (d) corresponded t o a weight l o s s of 12.1% of t h e i n -
55
In{KMTA)2Cl2*lOH20
Hg(HMTA)Gl2
Cu(KMTA)2Cl2
Zn(HI»ITA)Q ^^12*^4^20
Cd(KMTA)Q^^Cl2'i|H20
'
F i g u r e 26,
TEMPERATURE
TGA C u r v e s ,
^C
Air-Atmosphere
66
i t i a l sample weight or 76 a.m.u.
The t o t a l weight l o s s r e p r e s e n t e d
87.0% of t h e o r i g i n a l sample weight and i s i n good agreement with t h e
c a l c u l a t e d 87.89% f o r a f i n a l product of MnO.
The decomposition of Cu(HMTA)2Cl2 began a t 180*C with the r a p i d
l o s s of about 8.0% of t h e sample w e i g h t , approximately 33 a.m.u.
Al-
though weight l o s s was continuous u n t i l 700*C, t h e r a t e of decomposit i o n became very slow from 450* t o 480*C.
The t o t a l weight l o s s t o
t h i s p o i n t corresponded t o 33.8% of t h e sample weight of 136 a.m.u.
The f i n a l product was a p p a r e n t l y CuO, s i n c e t h e t o t a l weight l o s s was
80.0% of t h e t o t a l sample w e i g h t .
The c a l c u l a t e d value f o r CuO as
t h e product i s 80.82%.
The TGA curve f o r Hg(HMTA)Cl2 showed t h a t decomposition began
a t 190*C and was continuous u n t i l 700*C, where t h e weight l o s s was
100% of t h e i n i t i a l sample w e i g h t .
At 370*C t h e curve showed an a p -
p r e c i a b l e change in t h e r a t e of decomposition.
The weight l o s s a t
t h i s p o i n t was e q u i v a l e n t t o t h e l o s s of one mole of HgCl2 p e r mole
of complex, but t h i s could have been a f o r t u i t o u s
result.
The TGA curve of Zn(HMTA)o.5Cl2*4H20 showed dehydration o c c u r r i n g
between 140* and 210*C, p o i n t s ( a ) and (b) r e s p e c t i v e l y .
The p o r t i o n
of t h e curve from 210*C t o the f i n a l product of ZnO a t 660*C gave no
i n f o r m a t i o n with r e g a r d t o decomposition i n t e r m e d i a t e s .
The curve f o r Cd(HMTA)o.5Cl2*4H20 i n d i c a t e d t h a t t h e w a t e r of
h y d r a t i o n was l o s t between 60* and 180*C.
Decomposition of t h e amine
o c c u r r e d i n t h e temperature range of 240* t o 550*C.
The f i n a l product
was CdCl2, s i n c » t h e t o t a l weight l o s s was 43.4% of t h e sample weight
67
which i s i n good agreement with the c a l c u l a t e d value of 43.9%.
Thermogravimetric S t u d i e s in Vacuo
The TGA c u r v e s , in vacuo^
for the c o b a l t ( I I ) hexamethylenetetra-
mine complexes are shown i n Figure 27.
A l l water of h y d r a t i o n was
l o s t a t ambient t e m p e r a t u r e s .
The TGA curve of Co(HMTA)2Cl2 i n d i c a t e d , by s u c c e s s i v e l o s s e s of
34.2% of t h e o r i g i n a l sample w e i g h t , t h a t the two amines were l o s t i n
successive s t e p s .
The l o s s of t h e f i r s t amine s t a r t e d a t 140*C and
was complete by 185*C; t h e second amine was l o s t between 225* and
300*C.
Although t h e two decomposition s t e p s were s e p a r a t e d by 40*C,
a p e r f e c t p l a t e a u between t h e two r e a c t i o n s was never o b t a i n e d .
No
f i n a l p l a t e a u was o b t a i n e d due t o t h e sublimation of C0CI2.
The TGA curve of Co(HMTA)2Br2 showed s u c c e s s i v e weight l o s s e s
of 28.1%.
Decomposition of t h e f i r s t amine began a t 150*C and was
completed a t 225*C.
The second amine began t o decompose immediately
and t h e r e a c t i o n was completed a t 300*C.
Only an i n f l e c t i o n p o i n t
marked t h e s e p a r a t i o n of t h e two r e a c t i o n s t e p s .
The c o n p l e x , Co(HMTA)2l2> began t o decompose slowly a t 200*C and
t o t a l decomposition was completed by 375*C.
The decomposition was ap-
p a r e n t l y s t e p w i s e , but only a s l i g h t change i n t h e r a t e a f t e r t h e
l o s s of 23.6% of t h e sample weight marked t h e s e p a r a t i o n of t h e two
deamination s t e p s .
The curve of Co(HMTA)2(N03)2 i n d i c a t e d t h a t deamination began
a t 125*C and t h a t t h e l o s s of t h e f i r s t amine was complete a t 175*C.
Oxidation by t h e n i t r a t e group began immediately a f t e r t h e f i r s t
de-
68
A — Co(HiY.TA)2Cl2
B — Co(HMTA)2Br-2
)2l2
Oo(NO^)
5'2
CO
CO
o
20fo
100
I
200
3,00
TEMPERATTJRE
Figure 2?.
3i
^C
TGA C u r v e s , i_n Vacuo
500
600
69
amination s t e p .
The f i n a l product was Co30^ s i n c e t h e t o t a l weight
l o s s was 82.0%; t h e c a l c u l a t e d value for 0030^ i s 82.7%.
Shown i n Figure 28 a r e t h e TGA c u r v e s , in vacuo,
series.
for the nickel
The decomposition of t h e Ni(HMTA)2Cl2 and Ni(HMTA)2Br2 com-
p l e x e s , as shown by t h e TGA c u r v e s , involved stepwise deamination
r e a c t i o n s , b u t only changes in t h e r a t e of decomposition a f t e r t h e
l o s s of 34.4% and 28.2% of t h e sample w e i g h t s , r e s p e c t i v e l y , marked
t h e s e p a r a t i o n of t h e two s t e p s .
The TGA curve of Ni(HMTA)2l2 gave
no i n d i c a t i o n t h a t t h e amines were l o s t i n s t e p s .
The curve of
Ni(HMTA)2S0i| showed t h a t decomposition began a t 215*C and was c o n t i n uous u n t i l 700*C where the f i n a l product of NiO was o b t a i n e d .
The TGA curves for t h e remaining complexes s t u d i e d are shown in
Figure 29.
The decomposition of Cd(HMTA)o.5CI2 s t a r t e d a t 250*C and
was continuous u n t i l sublimation of CdCl2 was completed a t 650*C. The
small i n f l e c t i o n p o i n t i n the TGA curve a t 355*C corresponded t o t h e
l o s s of 1/2 mole of amine p e r mole of complex.
The curve of Zn(HMTA)0,5012 showed t h a t decomposition began a t
100*C.
The r e a c t i o n became q u i t e r a p i d a t 250*C and was continuous
u n t i l s u b l i m a t i o n of ZnCl2 was completed a t 630*0.
The weight l o s s
a t 250*0 was l e s s than t h e r e q u i r e d amount f o r 1/2 mole of amine, b u t ,
s i n c e 250*0 i s t h e approximate m e l t i n g p o i n t of ZnCl2, i t i s l i k e l y
t h a t both deamination and s u b l i m a t i o n were o c c u r r i n g simultaneously
at t h i s temperature.
The compound, Mn(HMTA)2Cl2, s t a r t e d decomposing a t 110*0 with
continuous weight l o s s u n t i l t h e f i n a l product of MnCl2 was o b t a i n e d
70
;;i(KMTA)2S0|
'4-
B
Kl(HMTA)2l2
C
D
r:i(HMTA)20l2
CO
CO
o
tA
CO
M
20^
TEMPERATURE
Figure 28.
TGA C u r v e s ,
^C
xr\ Vacuo
71
A
Cd(HMTA)Q r C l 2
B
Zn(IiMTA)Q c 0 l 2
C
Iun(EMTA)2Cl2
D
Cu(mTA)2Cl2
CO
CO
o
B-*
1-5
20,^
100
L_
200
_]
300
I
TEMPERATUra J i
Figure 29.
ij.00
500
I
I
O'^
TGA C u r v e s , iri Vacuo
600
72
a t 610*0.
The curve furnished no information regarding the mode of
de compos i t i on.
The Cu(HMTA)2Cl2 began t o decompose at 175*0 and the loss of the
f i r s t amine was complete at 275*0, where the r a t e of decomposition
decreased s l i g h t l y .
The loss of the second amine was accompanied by
the reduction of copper(II) chloride t o copper(I) chloride.
This r e -
duction was indicated by a t o t a l weight loss of 75.7% of the i n i t i a l
sample weight.
The calculated percentage of t o t a l weight losses for
Cu, CuCl, and CuCl2 as f i n a l products are 84.49%, 75.81%, and 67.40%,
respectively.
Infrared Absorption Spectroscopy Studies
The infrared absorption spectra of the complexes were obtained
a t ambient as well as at various elevated temperatures.
of Co(HMTA)2Cl2*10H20
The spectra
a t various temperatures are shown in Figure
30, and are representative of those obtained for the other complexes.
At 35*0, curve A, the spectrum showed absorption c h a r a c t e r i s t i c
of both water and hexamethylenetetramine.
The band from 2.8 y t o
3.4 p, the peak at 6.0 y, and general absorption in the 12 y t o 15 y
range were a t t r i b u t e d t o the water of hydration, the remaining peaks
t o the amine.
By 130*0, curve B, dehydration was complete as e v i -
denc^ed by the disappearance of the water bands.
The r e s u l t i n g spec-
trum i s c h a r a c t e r i s t i c of hexamethylenetetramine.
Curve 0 shows the infrared spectrum of the complex at 230*C,
j u s t a f t e r the f i r s t decomposition step of the anhydrous compound.
The complete lacJc of the c h a r a c t e r i s t i c hexamethylenetetramine spec-
73
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74
trum i n d i c a t e d t h a t decomposition did not involve stepwise deamination.
The spectrum showed a b s o r p t i o n only a t 3.0 y and in t h e range of
5.8 y t o 7.0 y.
The small peak a t 3.0 y i s c h a r a c t e r i s t i c of n i t r o g e n
t o hydrogen s t r e t c h v i b r a t i o n .
Although t h e n i t r o g e n t o hydrogen bend
v i b r a t i o n occurs w i t h i n t h e 5.8 y t o 7.0 y r e g i o n , t h e t o t a l band
could not be accounted f o r s o l e l y on t h i s b a s i s .
Only the aromatic
carbon t o carbon s t r e t c h v i b r a t i o n adequately accounted f o r t h i s band.
Q u a l i t a t i v e t e s t s on t h e decomposition products obtained a t 300*C did
show t h e presence of free carbon.
Calorimetric Studies
The d i f f e r e n t i a l scanning c a l o r i m e t e r from which t h e e n t h a l p i c
curves were o b t a i n e d was found t o have a much g r e a t e r s e n s i t i v i t y i n
t h e d e t e c t i o n of i n t e r m e d i a t e h y d r a t e s than conventional DTA.
Upon
d e h y d r a t i o n , t h e c o b a l t ( I I ) halo-complexes, as shown i n t h e e n t h a l p i c
curves of Figure 3 1 , l o s e a l l ten waters s i m u l t a n e o u s l y .
The n i c k e l
c h l o r i d e and bromide coii5)lexes undergo a two-step d e h y d r a t i o n .
The
curves i n Figure 32 show t h e two s t e p s w e l l s e p a r a t e d f o r
Ni(HMTA)2Cl2*10H20 but o v e r l a p p i n g i n the case of Ni(HMTA)2Br2'10H20.
The curve of t h e nicdcel icxiide complex gave no i n d i c a t i o n of t h e
formation of an i n t e r m e d i a t e h y d r a t e .
The e n t h a l p i c curves f o r Cd(HMTA)o.5Cl2*'+H20, Mn(HMTA)2Cl2-10H20,
and Zn(HMTA)o.5012*4H2O are shown i n Figure 3 3 .
Dehydration of t h e
cadmium complex occurred as an o v e r l a p p i n g t w o - s t e p r e a c t i o n , whereas
t h e z i n c and manganese complexes l o s t a l l w a t e r of h y d r a t i o n s i m u l taneously.
75
Co(HMTA)2Cl2^10K20
o
CO
Co(HMTn)2Br2•lOHoC
w
^
,.3
550
55,0
300
5'70
1;10
•
TEiv^PERATURE
Figure 5I.
Differential
^K
Scanning Calorimeter
Curves
76
:U(nKTA)2Cl2«10H20
rJ 1 (rhuTA ; 2 ^ ^ 2 •^^^•^"2
CO
o
a,
CO
-»r>
5;
5^0
^ /^ /^
1
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i:
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Figuro 52»' Differential Scanning Calorimeter Curves
77
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i u l . ' , i l . . . i r i . , ' 2 ^ - ^ ' > * J^'>^^-0*
cdCmiTA)
w
CO
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Zn ( HIV;TA)Q^C,C12 • -'-jH 2O
550
-J
i<lgur& 55.
550
7
L-
<^l^
L_
t 10
k 30
D i f f e r e n t i a l Scanning Calorimeter Curves
78
The h e a t s of dehydration o b t a i n e d from t h e e n t h a l p i c curves are
l i s t e d i n Table V.
Magnetic S u s c e p t i b i l i t y S t u d i e s
The magnetic moments c a l c u l a t e d from t h e magnetic s u s c e p t i b i l i t y
d a t a a r e shown i n Table VI.
R e f l e c t a n c e Spectroscopy S t u d i e s
The r e f l e c t a n c e s p e c t r a of t h e hydrated c o b a l t ( I I ) complexes and
f o r t h e anhydrous complexes, Co(HMTA)2S0i^ and Co(HMTA)2(N03)^, are
shown i n Figure 34.
A l l h y d r a t e d complexes of cobalt produced i d e n -
t i c a l s p e c t r a which were c h a r a c t e r i z e d by a major peak a t 500 my and
s h o u l d e r peaks a t 625 my and 470 my.
The r e f l e c t a n c e s p e c t r a of both
Co(HMTA)2S0^ and Co(HMTA)2(N03)i^ c o n s i s t of s i n g l e broad b a n d s , the
s u l f a t e with a maximum a t 550 my and t h e n i t r a t e with a maximum a t
535 my.
The r e f l e c t a n c e s p e c t r a of t h e anhydrous c o b a l t ( I I ) h a l i d e comp l e x e s a r e shown i n Figure 3 5 .
The spectrum of Co(HMTA)2Cl2 was c h a r -
a c t e r i z e d by a very s t r o n g band between 575 ray and 635 my, small fine
s t r u c t u r e peaks a t 480 my, 435 my, 420 my, and 380 my, and a s h o u l d e r
peak a t 525 my.
The r e f l e c t a n c e curve of Co(HMTA)2Br2 showed a s t r o n g
c h a r a c t e r i s t i c band between 600 my and 655 my, s m a l l f i n e s t r u c t u r e
peaks a t 450 my, 430 my, and 390 my, and s h o u l d e r peaks a t 540 my and
505 my.
The spectrum of Co(HMTA)2l2 had two s t r o n g b a n d s , t h e
first
from 750 my t o 625 my with a s h o u l d e r peak a t 535 my, and t h e second
from 500 ray on i n t o t h e u l t r a v i o l e t region with a s h o u l d e r peak a t
480 my.
79
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81
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C —^ All Hydrated Cobalt(Il) Complexes
i^oo
I1.50
Figure ^I;.,
500
550
LWAVELENGTH, riyi
Reflectance Spectra
600
L_
650
L_
700
L_
82
:MTA)-T
—
CO(K:UTA)2C12
—
Co{EIwTA)23r2
600
WAVELEKGTH, m^
' I g u r e 55*
Heflectarxe
Spectra
ip^
83
The r e f l e c t a n c e curves of t h e hydrated nicdcel complexes and
Ni(HMTA)2S0i+ are shown i n Figure 36.
All hydrated complexes had i -
d e n t i c a l s p e c t r a which were c h a r a c t e r i z e d by a band with a maximum a t
655 my, a sharp peak a t 390 my, and shoulder peaks a t 545 my and 450
my.
The spectrum of t h e anhydrous s u l f a t e complex was s i m i l a r in
shape t o t h o s e of t h e hydrated complexes but was s h i f t e d t o a h i g h e r
wavelength.
The band maximum was a t 710 my and t h e peak maximum a t
420 my.
The r e f l e c t a n c e curves of t h e anhydrous nicd<el h a l i d e complexes
and t h e i n t e r m e d i a t e h y d r a t e , Ni(HMTA)2Cl2*3H20, are shown i n Figure
37.
The curve of t h e 3-hydrate was s i m i l a r t o t h a t of t h e f u l l y h y -
d r a t e d compound but with t h e band maximum a t 705 my and t h e peak
maximum a t 425 my.
The r e f l e c t a n c e curve of Ni(HMTA)2Cl2 showed a
very s t r o n g band from 600 my t o 510 my, a s m a l l peak a t 435 my, and
t h e s t a r t of a n o t h e r s t r o n g band a t 405 my t h a t continued i n t o t h e
u l t r a v i o l e t region.
625 my t o 550 my.
The curve of Ni(HMTA)2Br2 had a s t r o n g band from
There was a small peak a t 440 my and s t r o n g a b -
s o r p t i o n from 425 ray on i n t o t h e u l t r a v i o l e t r e g i o n .
The r e f l e c t a n c e
curve of Ni(HMTA)2l2 showed t h e presence of two s t r o n g b a n d s , one
t a i l i n g i n t o t h e i n f r a r e d region and t h e o t h e r c o n t i n u i n g i n t o t h e
u l t r a v i o l e t region.
The two bands were s e p a r a t e d by a r e f l e c t a n c e
maximum (absorbance minimum) a t 565 my.
Shown i n Figure 38 are t h e r e f l e c t a n c e curves of Cu(HMTA)2Cl2,
Mn(HMTA)2Cl2*10H20, and Mn(HMTA)2Cl2.
The r e f l e c t a n c e curve of t h e
copper complex showed t h e presence of two s t r o n g bands with a r e f l e c t a n c e maximum between the two bands a t 610 ray. N e i t h e r of t h e r e -
84
/
\
A —
All Hydrated Nickel Complexes
B —
N1(HMTA)2S0.
\
o
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en
o
w
vVAVELElv^GTii
Figure 5^»
;,wi
Reflectance Spectra
85
550
I
WAVELENGTH, mya
Figure 57. Reflectance Spectra
600
L_
7,00
86
r
Figure 58, Reflectance Spectra
87
f l e c t a n c e curves of t h e two manganese complexes contained peak maxima.
I t has r e c e n t l y been demonstrated t h a t when decomposition r e a c t i o n s a r e c a r r i e d out i n t h e presence of a l a r g e p r o p o r t i o n of s o l i d
m a t r i x m a t e r i a l , t h i s m a t e r i a l may a l t e r t h e product of t h e r e a c t i o n
(45).
I t was of i n t e r e s t t o determine i f matrix anion exchange would
occur f o r dehydration r e a c t i o n s and i f t h i s exchange was favored o r
h i n d e r e d by a change i n the s t r u c t u r e of t h e bonding m e t a l .
The dehydration r e a c t i o n s of Co(HMTA)2X2*10H20 (where X i s C I ,
Br, or I ) and Co(HMTA)2S0it»10H20 were s t u d i e d i n t h e presence of
l a r g e p r o p o r t i o n s of v a r i o u s ammonium and sodium s a l t s .
The mixtures
were made up by weight u s i n g nine p a r t s of m a t r i x m a t e r i a l t o one p a r t
of complex, then ground and heated f o r 1 hour a t 110°C.
The r e s u l t i n g r e f l e c t a n c e s p e c t r a obtained from h e a t i n g
Co(HMTA)2S0^«10H20 t o llO^C in various sodium s a l t s are shown i n F i g u r e 39.
In Nal and NaBr m a t r i c e s , t h e s p e c t r a showed t h a t the matrix
anions e n t e r t h e c o o r d i n a t i o n sphere of the complex with the complete
e x c l u s i o n of t h e s u l f a t e .
In NaCl, Co(HMTA)2Cl2 was obviously t h e
major prcxiuct but t h e spectrum lacked t h e fine s t r u c t u r e peaks c h a r a c t e r i s t i c of t h e pure c h l o r i d e complex.
The spectrum of t h e f i n a l p r o -
duct of t h e dehydration i n NaF i n d i c a t e d t h e presence of only Co(HMTA)2S0it,
Dehydration of Co(HMTA)212*10^20 i n v a r i o u s sodium s a l t s (shown
i n Figure 40) prcxiuced compounds having i d e n t i c a l r e f l e c t a n c e
spectra.
These s p e c t r a corresponded e x a c t l y t o t h e spectrum of t h e pure anhydrous i o d i d e complex.
The r e f l e c t a n c e s p e c t r a of t h e dehydration of Co(HMTA)2Br2*10H20
i n v a r i o u s sodium s a l t s (Figure 41) a l l showed s t r o n g bands i n t h e
88
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r
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N/
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-50
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1^50
1_
500
•J
550
L-
WAVELENGTH^., m)i
Figure 59. Reflectance Spectra
600
650
700
89
n^ (
,Uo^n...TA)2l2*10H20
20
«
in
B — i n NaBr
C — i n Ka?
-50
B
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80
lioo
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500
550
WAVELENGTH, ..,;.
Figure IiO. Reflectance Spectra
600
L-
700
_i
90
.Co(H:.:TA)2Br2'iOH20
A — i n NaCl
• w
B — i n Nal
C — i n NaF
o
V/AV iLliii\ GTii, ;: j \
F i g u r e [j-l.
Reflectance
Spectra
91
500 my t o 655 my r e g i o n , c h a r a c t e r i s t i c of t h e anhydrous bromide complex.
In Nal t h e f i n e s t r u c t u r e peaks were absent and t h e r i s i n g a b -
s o r p t i o n from 450 my t o 350 my could be a t t r i b u t e d only t o t h e charge
t r a n s f e r band of Co(HMTA)2l2.
The r e f l e c t a n c e curves of the dehydration of Co(HMTA)2Cl2'10H20
(Figure 42) a l l i n d i c a t e d t h e formation of t h e anhydrous c h l o r i d e comp l e x as t h e major product but t h e small band from 450 my t o 350 my
i n t h e Nal m a t r i x i n d i c a t e d t h a t the iodide complex was a l s o formed
t o some e x t e n t .
The dehydration of Co(HMTA)2S0^•10H20 i n ammonium s a l t s i s shown
i n Figure 4 3 .
In a l l s a l t s except NH^F, the s p e c t r a r e p r e s e n t obvious
mixtures of t h e anhydrous s u l f a t e complex and t h e anhydrous complex
c o n t a i n i n g t h e anion of t h e m a t r i x .
The r e f l e c t a n c e curve of t h e p r o -
duct i n NHi^F was i d e n t i c a l t o t h a t of anhydrous c o b a l t ( I I )
fluoride.
The p r o d u c t s of dehydration of Co(HMTA)2l2*10H20 i n ammonium
s a l t s , shown by t h e curves i n Figure 44, had s p e c t r a i d e n t i c a l t o t h a t
of Co(HMTA)2l2 except i n NHi^F where t h e f i n a l product was C0F2.
The r e f l e c t a n c e curves of Co(HMTA)2Cl2*10H20 and Co(HMTA)2Br2IOH2O a f t e r dehydration ( F i g u r e s 45 and 46) i n d i c a t e d t h a t t h e dehyd r a t i o n r e a c t i o n was unaffected by t h e m a t r i x in NH^Cl and NHi^Br. In
NHj^I, however, both complexes formed a p p r e c i a b l e Co(HMTA)2l2 as e v i denced by t h e r i s i n g a b s o r p t i o n i n the 450 my t o 350 my r e g i o n .
The
f i n a l product i n NHi^F was again C0F2.
S i n c e , i n most c a s e s , anion exchange was i n c o m p l e t e , i t seemed
l i k e l y t h a t i n t i m a t e c o n t a c t between t h e complex and m a t r i x was n o t
o b t a i n e d , even a f t e r thorough g r i n d i n g .
To i n c r e a s e t h e c o n t a c t b e -
92
O(H:.:TA)_CI^«IOHOO
^0
_ c
2
2
^
A -— I n NuBr
B
i n Nai
i n NaF
-50
o
<
EH
O
cr:
..•'/"*
liOO
I
450
Figure 1|2.
500
..J
600
550
LWA VELSC GTH
•h
Reflectance Spectra
650
700
93
\ -
?.0
• • •
^
D — i n NH, Cl
4
1
^
4 00
450
f- P ; /-N
err*
•.Ay J
^
v^,ij:Li'.GTi:,
m^
r'lgure q.5.. Reflectance Spectra
700
94
--A
W
•A
w
o
'Igure I|i^.
Reflectance Spectra
95
'^"«..^ D
J
j_
Figure 1^5•
li
Reflectance
1:^
0
S-pectra
' 1'"'
96
2C
.-. — i n i\rj,or
— i n KIT, I
i n u.^-l; ;p^'-'!
F i g u r e h^b.
Reflectance
Spectra
97
tween complex and m a t r i x s a l t , t h e two were thoroughly mixed and then
p r e s s e d a t a p r e s s u r e of 20,000 l b . / i n . 2 f o r 15 minutes.
The r e s u l t -
i n g p e l l e t s were ground t o a fine powder and heated f o r 1 hour a t 110<>C,
The r e f l e c t a n c e s p e c t r a of Co(HMTA)^S0i+«10H20 i n various sodium
h a l i d e s a l t s are shown in Figure 47.
In a l l cases anion exchange was
c o m p l e t e , with the s p e c t r a of t h e pure anhydrous h a l i d e complexes being
obtained.
The r e f l e c t a n c e s p e c t r a of Co(HMTA)2l2*10H20 in NaCl and NaBr
( F i g u r e 48) showed t h e m a t r i x t o have no e f f e c t on the course of dehydration.
In both c a s e s , t h e spectrum of t h e pure anhydrous i o d i d e
complex was o b t a i n e d .
Shown i n Figure 49 a r e t h e r e f l e c t a n c e s p e c t r a of t h e dehydration
of Co(HMTA)2Br2*10H20 i n NaCl and Nal.
The spectrum of t h e f i n a l p r o -
duct i n NaCl was i d e n t i c a l t o t h a t of t h e anhydrous bromide complex.
In N a l , t h e spectrxim of Co(HMTA)2l2 was o b t a i n e d .
The s p e c t r a of t h e dehydration products of Co(HMTA)2Cl2*10H20 i n
NaBr and Nal a r e shown i n Figure 50.
The spectrum of t h e product i n
NaBr was i d e n t i c a l t o t h a t of Co(HMTA)2Br2; i n Nal t h e spectrum showed
t h e f i n a l product t o be Co(HMTA)2l2The r e s u l t s o b t a i n e d f o r t h e dehydration of the complexes i n
ammonium s a l t s were i d e n t i c a l t o those of t h e sodium s a l t s .
98
-70
Co(IiI.:TA)^SO, -lOH^O
1
n.r\
Si
Figure 1|7»
rnn
A —
in Nal
B —
in NaBr*
C —
in Nal
r r '^
Reflectance Spectr
600
99
[|00
-J
:0
Figure [{.S.
r i^r^
5'^0
600
1
Reflectance Spectra
"o;
• I
100
Co(H:/:TA)p3r^.lOH20
A — i n Nal
gui'fi 1|9«
Reflectance
Spectra
101
Co(r!ilTA),Clo'10H-0
/
/
\
\
/
\
/
\
/
^so
30
Ii50
500
600
550
VA
Figure ^0.
Reflectance Spectra
"0
7 oc
102
Discussion and Conclusion
The TGA curves, in vacuo,
for the hexamethylenetetramine complexes
indicated that decomposition occurs, in general, by stepwise deamination.
Even those complexes for which the two steps could not be dif-
ferentiated gave final weight losses indicative of total amine sublimation.
Decomposition in air, however, was shown by the TGA curves to
involve more than simple stepwise deamination reactions.
The high
temperature infrared spectra of the complexes showed only the presence
of carbon to carbon and nitrogen to hydrogen bonds indicating the
following mode of decomposition:
• 8NH3 i- 12C + MX2-
MC(CH2)6N^]2X2
The air TGA curves of all complexes, except that of manganese,
were in excellent agreement with this raode of amine decomposition. The
curves of the cobalt and nickel complexes indicated that two moles of
ammonia were initially retained, forming diamine complexes.
The two
remaining ammonia molecules were lost slowly leaving the metal salt
and free caii)on.
The final step in the decomposition was air oxidation
leaving the metal oxide as a final product.
290°
MC(CH2)6N^]2X2
M(NH3)2X2
MX2
+
12C
> M(NH3)2X2
2950-50OO
+
> MX2
XO2 -^^—
+
The three reactions were:
^
12C
+
6NH3
2NH3
• Metal Oxide
-l- I2CO2
+
The weight-loss curves of the copper complex showed the initial
evolution of only two moles of ammonia as decomposition of the amine
X2.
103
o c c u r r e d , t h u s forming t h e s t a b l e CCu(NH3)6]Cl2 as an i n t e r m e d i a t e .
The manganese complex d i s s o c i a t e d by t h e s i m i l t a n e o u s sublimation
of one amine and decomposition of t h e second.
complexes were formed.
The decomposition proceeded by t h e following
steps:
J
Mn[(CH2)6Ni»]2Cl2
6C
No i n t e r m e d i a t e amine
t
6O2
«w «,
2MnCl2
+
^QQ^^-^^OQ ^ ^^^^
^^Q"-^^Q^
^
O2
+ 6C + 4NH3 + (CH2)6Ni»
6CO2
550**-650®
-^^—
> 2MnO •»• 2Cl2«
Considerable evidence f o r t h e s t r u c t u r e of t h e c o b a l t and n i c k e l
complexes was o b t a i n e d by t h e r e f l e c t a n c e and magnetic s u s c e p t i b i l i t y
studies.
The s p e c t r a of the hydrated c o b a l t complexes were i n e x -
c e l l e n t agreement with t h e w e l l - c h a r a c t e r i z e d s p e c t r a of o c t a h e d r a l
c o b a l t ( I I ) compounds(46).
These con5)ounds appeared t o have no m e t a l -
t o - a n i o n bond s i n c e t h e s p e c t r a were a l l i d e n t i c a l and independent of
the anion.
There must, however, have been bonding between c o b a l t and
t h e amine s i n c e t h e s p e c t r a maxima were s h i f t e d from 540 my i n
Co(H20)52'*' t o 505 my i n the hydrated complexes.
This i s t h e d i r e c t i o n
expected f o r t h e i n c r e a s e d f i e l d s t r e n g t h of t h e amine.
The anhydrous compounds, Co(HMTA)2Cl2, Co(HMTA)2Br2, and
Co(HMTA)2l2» were a p p a r e n t l y t e t r a h e d r a l i n s t r u c t u r e .
A l l had very
s t r o n g a b s o r p t i o n bands in t h e red p o r t i o n of t h e spectrum with s m a l l
f i n e s t r u c t u r e peaks t a i l i n g off t o t h e v i o l e t s i d e , which i s c h a r a c t e r i s t i c of t h e c o b a l t ( I I ) t e t r a h e d r a l c o n f i g u r a t i o n ( 2 9 ) .
The h a l i d e
i o n s were bonded d i r e c t l y t o the metal i n t h e s e complexes s i n c e t h e
s p e c t r a were dependent upon t h e h a l i d e ion p r e s e n t .
The n i t r a t e and
104
s u l f a t e complexes a p p a r e n t l y remained i n an o c t a h e d r a l s t r u c t u r e upon
dehydration.
The magnetic moments of t h e c o b a l t ( I I ) complexes were in e x c e l l e n t
agreement with t h e s p e c t r a l assignments.
High spin o c t a h e d r a l compounds
g e n e r a l l y have magnetic moments from 4.7 t o 5.2 B.M.(13) which c o r r e l a t e s w e l l with t h e values o b t a i n e d f o r t h e hydrated compounds.
Mo-
ments of t e t r a h e d r a l c o b a l t ( I I ) compounds are g e n e r a l l y in the range of
4 . 1 t o 4.9 B.M., a g r e e i n g n i c e l y with t h e values obtained f o r t h e a n hydrous h a l i d e complexes.
Low spin o c t a h e d r a l s t r u c t u r e s were e l i m -
i n a t e d s i n c e they have magnetic moments of 1.8 t o 2.0 B.M.
A l l t h e h y d r a t e d n i c k e l complexes, as in the case of c o b a l t , had
i d e n t i c a l s p e c t r a which agreed n i c e l y with t h e r e p o r t e d s p e c t r a of
n i c k e l ( I I ) o c t a h e d r a l compounds(47).
The r e f l e c t a n c e spectrum of t h e
anhydrous Ni(HMTA)2S0it a l s o showed i t t o be o c t a h e d r a l .
The r e f l e c t a n c e s p e c t r a of t h e anhydrous h a l i d e compounds, howe v e r , d i f f e r e d g r e a t l y from t h o s e expected f o r compounds with an o c t a hedral structure.
The square p l a n a r s t r u c t u r e , which i s a l s o q u i t e
common f o r n i c k e l ( I I ) , was r e a d i l y e l i m i n a t e d as a p o s s i b i l i t y s i n c e
t h i s s t r u c t u r e would be d i a m a g n e t i c .
The only o t h e r r e p o r t e d s t r u c -
t u r e f o r n i c k e l ( I I ) i s t h a t of t e t r a h e d r a l f o r which only a very few
cases; have been confirmed.
The s p e c t r a of t e t r a h e d r a l n i c k e l ( I I )
complexes a r e c h a r a c t e r i z e d by a s t r o n g absorbance band i n the 500
my t o 800 ray r e g i o n ( 4 8 , 4 9 ) .
All t h e anhydrous n i c k e l halo-coraplexes
have s t r o n g bands i n t h i s r e g i o n .
The raagnetic moments of o c t a h e d r a l n i c k e l ( I I ) complexes range
between 2.83 ( t h e s p i n - o n l y v a l u e ) and 3.4 B.M.(13).
Tetrahedral
105
compounds with four i d e n t i c a l ligands or compounds containing ligands
which are c l o s e together i n the spectrochemical s e r i e s have moments
of 3.7 t o 4.0 B.M.
I f , however, the ligands have appreciable separa-
t i o n in the spectrochemical s e r i e s , as i s most c e r t a i n l y the case of
hexamethylenetetramine and the halidesi, the magnetic moments are in
the same lower range as those of the octahedral compounds.
It i s i n -
t e r e s t i n g t o note that in every c a s e , the anhydrous halide compounds
had raagnetic raoments greater than t h e i r octahedral hydrated counterparts , which i s the required trend i f they are t o be tetrahedral in
structure.
The caloriraetric s t u d i e s a l s o showed a trend with respect t o
change in s t r u c t u r e .
The heats of dehydration for the cobalt and
n i c k e l complexes, where dehydration produces the r e l a t i v e l y unstable
tetrahedral s t r u c t u r e s , were quite high.
The zinc and cadmium com-
p l e x e s , which have tetrahedral structures that are generally more
s t a b l e than the octahedral, have rauch lower heats of dehydration.
Mercury, which forms tetrahedral complexes almost e x c l u s i v e l y , i s prepared as the anhydrous compound.
The manganese complex i s the only complex not t o f i t i n t o a def i n i t e pattern.
I t s heat of dehydration was found t o be quite high;
i t i s the only complex for which the TGA s t u d i e s indicated a d i f f e r e n t
mode of decomposition; and the r e f l e c t a n c e spectra gave no i n d i c a t i o n
of a change of structure upon dehydration.
A number of important conclusicffis may be drawn from the matrix
anion exchange s t u d i e s .
F i r s t , s o l i d s t a t e matrix exchange reactions
are not l i m i t e d t o the type of amine decomposition reactions reported
106
by Sterabridge(45) but are considerably more general.
I f the proper
r e a c t i o n conditions and matrix material are used, the technique appears applicable t o any w e l l defined decomposition reaction involving
the f r e e i n g of a coordination p o s i t i o n .
Second, unlike the reactions reported by Stembridge, the matrix
cation did not appear t o be involved i n the s u b s t i t u t i o n r e a c t i o n .
Third, intimate contact between the complex and matrix appears
t o be the e s s e n t i a l c r i t e r i o n for quantitative anion exchange.
Such
contact cannot be obtained by simple grinding.
L a s t l y , the preferred order of the ions for matrix exchange i s
dependent upon the coordinating metal.
c o b a l t ( I I ) complexes was F<<Cl<Br<I.
The order observed for the
This i s the reverse order ob-
t a i n e d by Stembridge for the chromium(III) complexes.
The difference
i n the preferred order of exchange might well be due t o the d i f f e r ences i n the type of bonding of the two s e r i e s .
The order determined
for the chromium(III) complexes follows the spectrochemical s e r i e s ,
which, for the halide i o n s , i s the order of increasing sigma bond
formation.
The order F<Cl<Br<I r e f l e c t s an increase in the a b i l i t y
t o form ir-bonds.
Since the c o b a l t ( I I ) complexes were found t o be c o -
ordinated by outer o r b i t a l 4s4p^4d^ bonds or r e l a t i v e l y unstable
4s4p^ bonds, ir-bonding would be expected t o be of great importance in
s t a b i l i z i n g complex formation.
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