THE INTERACTIO
INTERACTION
SILICON
TETRAFLUORIDE
WITH
METHANOL
N OOF
F SILICO
N TETRAFLUORID
E WIT
H METHANO
L
J . P.
P . GUERTIN
GUERTIN AND M.
M . ONYSZCHUK
ONYSZCHUK
lnorganic
Chemistry Laboratory,
Laboratory, Department
Departmentofof Chemistry,
Chemistry, McGill
lvlcGill University,
University, Montreal,
.illontreal, Que.
Que.
Inorganic Chemistry
J.
Received January
January 7, 1963
ABSTRACT
ABSTRACT
. Silicon tetrafluoride reacts with methanol in a 1:4
1:4 mole ratio, forming the complex
SIF
SiF4.4CH30H,
—20° and is completely dissociated in the
4 .4CH aOH, which freezes to a glass at about -20°
gaseous phase at 25°. Conductivity
Conductivity measurements show clearly that
that it is a very weak electrolyte
electrolyte
in methanol solution. Its infrared
infrared spectrum
spectrum does not contain an Si-O
Si—O bond stretching absorption band. Proton magnetic resonance measurements provide strong evidence of hydrogen
bonding between silicon tetrafluoride
tetrafluoride and methanol. These results indicate that
that the structure
structure
tetracovalent rather
rather than hexacovalent
hexacovalent silicon and strong hydrogen
of the complex requires tetracovalent
bonds between methanol and each of the four fluorine atoms.
I;\TTRODUCTIO~
INTRODUCTION
Many
Many complexes of silicon tetrafluoride
tetrafluoride with nitrogen electron-pair
electron-pair donor molecules
have been prepared
prepared and characterized
characterized (1-7); less is known about the interaction
interaction of silicon
tetrafluoride
tetrafluoride with oxygen donors. Muetterties (6) has described SiF
SiF4.2(CH3)280,
4 .2(CH a)2S0,
SiF
of
SiF4.2(CH3)2NCHO,
SiF4.xCH3COCH2COCH3;
4 .xCH aCOCH 2COCH a; the last is a very weak complex of
4 .2(CH a)2NCHO, and SiF
uncertain composition. Gierut
al. (8) reported briefly
briefly that
uncertain
Gierut etet al.
that silicon tetrafluoride
tetrafluoride reacts
1:4 mole ratio, yielding unstable addition compounds SiF
SiF4.4ROH,
with alcohols in a 1:4
4.4ROH,
CH3, C
C2H5,
iso-C3H7,
iso-CsHn;
confirmed by Topchiev
Topchiev
where R is CHa,
6 H u ; these results were confirmed
aH 7 , and iso-C
2H 6 , iso-C
Bogomolova (9), who also suggested that
that the complex is ionic and contains hexaand Bogomolova
covalent silicon. However, Holzapfel
Holzapfel etet al.
that silicon tetrafluoride
tetrafluoride and
covalent
al. (10) reported that
1:6 and 1:8
1:8 complexes only. With the object
object of clarifying
clarifying these conmethanol produce 1:6
flicting results, we have investigated
investigated the interaction
interaction of silicon tetrafluoride
tetrafluoride with methanol
methanol
flicting
using tensimetric titration, conductivity, infrared,
infrared, and proton magnetic resonance
investigation of the relative electron acceptor
acceptor
methods. This research is part
part of a general investigation
power of silicon and germanium
germanium tetrafluoride
tetrafluoride towards oxygen, sulphur, nitrogen, and
phosphorus electron-pair
electron-pair donor molecules. This paper describes the peculiar nature of
of
tetrafluoride - methanol system.
the silicon tetrafluoride
RESUL
TS AND DISCUSSION
RESULTS
Preparation
Preparationofof SiF^.^CH^OH
SiF 4 .4CH30H
Silicon tetrafluoride
tetrafluoride (in excess) and methanol when slowly mixed together in a VaCUUlTI
vacuum
at 25° produced
produced the 1:4
4 .4CH aOH, a colorless liquide
1:4 complex, SiF
SiF4.4CH30H,
liquid. It formed a glass at
at
about
20° and was completely
about -—20°
completely dissociated in the gaseous phase at 25°. The 1:4
1:4 combining
combining
ratio was not always reproducible and values in the range 1.00:3.75 to 1.00:4.20 were also
obtained. Ratios lower th
an 1:4
than
1:4 are attributed
attributed to the formation
formation of sorne
some dimethyl ether
by the silicon tetrafluoride
tetrafluoride catalyzed
catalyzed dehydration
dehydration of methanol (9); higher ratios are
probably due to incomplete reaction of methanol with silicon tetrafluoride. The combining
probably
combining
ratio was never 1:6
or
1:8,
as
claimed
by
Holzapfel
et
al.
(10).
1:6
Holzapfel et
(10).
A tensimetric titration of silicon tetrafluoride
with
methanol
(Fig. 1) confirmed
tetrafluoride
confirmed the
formation
formation of only a 1:4
1:4 complexe
complex. After
After each successive addition of methanol to silicon
tetrafluoride
tetrafluoride in this titration, the mixture was warmed to 25° and then cooled to -78°,
—78°,
at which temperature
temperature pressure measurements were made. As shown in Fig. 1 the pressure
decreased linearly and approached
approached zero after
after the mole ratio of methanol to silicon tetraCanadian Journal of Chemistry. Volume 41
41 (1963)
1477
: A N A D I A N JOURNAL
J O U R N A L OF
O F CHEMISTRY.
C H E M I S T R Y , VOL.
V O L . 41,
41. 1963
1963
C.\NADIAN
1478
1478
300----------------------~
270
240
180
E
E
150
w
a:
:::> 120
(/)
(/)
w
a:
a..
30
OL-~~~~~--~~~--~
3 4
4
1 1 2 32
5 56
MOLE RATI
RATIO
CH,JOH/SiF44
O CH30H/SiF
o0
FIG.
F I G . 1.
Tensimetric titration of silicon tetrafluoride
tetrafluoride with methanol.
methanol.
ftuoride
an 4; extrapolation of the linear portion to zero pressure
fluoride becan1e
became greater th
than
pressure
tetrafluoride
indicates a mole ratio of 4.2. In the reverse titration of methanol with silicon tetraftuoride
CH30H/SiF4
when
(Fig. 2), the pressure remained zero until the mole ratio CH
30I-IjSiF 4 decreased to 5, when
2
50
250r---------------------------------~----~
~
o
REPRESENT TWO SEPARATE
DETERMINATIONS
200
w
a::
::::>
1/)
1/)
,1
,,
w
a: 100
(L
1
,
,,1
,,,
1
1
1
50
1
,
7
MOLE RATIO
RATIO
FFIG,2.
I G . 2.
,,,
654
CH30H/Si^
CH 3 0H/Sl'4
3
2
Tensimetric titration
titration of
of methanol
methanol with
'th sili
'l'
Tensimetric
WI
SI icon
Icon tetrafluoride.
tetrafluoride.
1479
GUERTIN
G U E R T I N AND ONYSZCHUK: SiF,-CHaOH
SiFi-CHjOH INTERACTION
INTERACTION
the pressure increased rapidly as the ratio decreased further;
further; extrapolation
extrapolation of the linear
part
part of this plot to zero pressure gives a mole ratio of 3.8;),
3.85, corresponding
corresponding to the formation
formation
of :he
the 1:4
1:4 complex, SiF
SiF4.4CH30H.
conclusively that
that
4.4CH30H. The two tensimetric titrations show conclusively
1:6 and 1:8
1:8 complexes are not produced. Attempts were made to measure the dissociation
1:6
pressure of SiF
SiF4.4CH30H,
therefore the heat of
but the values were not reproducible and therefore
of
4.4CH 30H, but
dissociation of the complex could not be obtained.
obtained.
ConductivÜy
SiF 4 .4CH30H
Conductivity ofof SiF^.^CH^OH
The conductivity
4.4CH 30H in methanol \-vas
conductivity of SiF
SiF4.4CH30H
was measured to test the suggestion
(9) that
that this complex has the ionic structure l,
I, in which methoxy groups may be in
H CH^
22-
OCH
OCH.3
j",-t-/-7F
1
St
1
F~-t~'~
2CH30H2^
2CH
0H2+
3
p^
OCH3
H C
lI
K
H
either
either cis or trans arrangement. The conductivity
conductivity measurements are given in Table 1I and
plotted in Fig. 3, where they are compared
plotted
compared with the molar conductances of acetic acid (11)
TABLE
TABLE 1
I
Conductivities of SiF
4. 4CH 3 0H in methanol
SiF4.4CH30H
SiF4.4CH30H
SiF
4. 4CH 3 OH
concentration
concentration c,c,
mole 1~^
1-1
3.75
3.75
1.87
1.87
0.47
0.47
0.0094
0.0094
0.00090
0.00090
0.00019
0*
Specific
conductance k,k,
mho cmcm~i1
Molar
conductance jj,.
J.1.,
mho cm
1-1
cm^2 (g-mole)-1
(g-mole)"^ 1"^
3.0X10-33
3.0X103.0X103.0X10-33
l.
OX 10-3
1.0X10-3
4.0X104.0X10-44
1.
2X10- 4
1.2X10-4
4.7X104.7X10-5s
5.
OX 10- 6
5.0X10-6
0.80
0.80
1.60
1.60
2.13
42.7
133
250
—
l/2 ,
C
c"\
(mole 1-1)^/2
1-1)112
1.94
1.94
1.37
1.37
0.685
0.097
0.030
0.030
0.014
0.014
—
l•
(12)) value: 5X
5X10-8
cm-i.
*Pure methanol (lit. (12»
10-8 mho cm-
and sodium chloride (12) in lnethanol.
methanol. The results and comparisons reveal that
that
SiF
4.4CH aO H is a very weak electrolyte in methanol; therefore, structure 1I or any other
SiF4.4CH30H
structure is not valid. Using an empirical method recently described by Levitt
Levitt (13),
ionic structure
2
estimated a molar conductance
conductance at infinite
infinite dilution of 830 mho cm
cm- (g-mole)-l
(g-mole)~^ l~^
for
1-1 for
we estimated
5
1
equilibrium constant
constant for dissociation of 2.76 X
X10~^
the complex, an equilibrium
10- mole l~\
1- , and a degree
1
of dissociation of 4.8% for a solution of 0.01 mole 11~^ concentration.
concentration.
Infrared Spectrum
lnfrared
Spectrumofof SiF^./iCH-iOH
SiF 4 .4CH30H
An alternative structure, II, involves octahedral
octahedral bonding of silicon and hydrogen
hydrogen
bonding between methanol and each of the coordinated
coordinated methanol molecules. The infrared
infrared
spectrum of such a species should con
contain
Si—O bond stretching
stretching absorption
absorption band;
band;
spectrunl
tain an Si-O
F CHEM ISTRY . VOL. 41, 1963
CANADIAN
JOURNAL
CANAD
IAN JOURN
AL 0 OF CHEMISTRY. VOL. 41, 1963
1480
1~80
I~
ï
W
250
- 4 C H 330H
0 H
• • SSl..^~·4CH
•
N
a
C
l
(Ref.l2
• NaCL (Ref. 12) )
• A CH
CH3COO
(Ref .Il)
11)
COOHH(Ref.
3
.-l
o
~
~200
~~
u
o
1:
~
w
U
Z
~
U
::l
a
z
o
u
cr
«
.J
o
~
5
o
10
15
20
25
~
50
100
150
200
2
(CONC
ENTRA TION{Z - (MOLES/LITER)'-^
(MOLE SjLITE R) '12.^ X
(CONCENTRATIONf^X 10
10 '
FIG.
FIG.
4CH OH NaCl
and CH 3 COOH in
parison of
3. Cam
Comparison
of the
the molar
molar conduc
conductances
SiF4.4CH30H,
in metha
methanol.
nol.
tances 0off S·F
3.
1 4·
3 , NaCl,, and CH3COOH
this
ly very stron
g
this is
is usual
usually
strong
alkyld
isiloxanes (15).
alkyldisiloxanes
(15). Since
100
,
N
80
and
and occur
occurss at 10851085-1105
c m ' il i.n
in ~et~o
methoxysilanes
(14) and
1105 cmxysilanes (14)
a?d
the
4CH
infrar
0
the infrared
spectra
(Fig. 4)
4) of
of hquld
liquid SlF
SiF4.4CH30H
and
its
ed spect
ra (Fig.
4.
3 H and Its
\ {""-----------'---------·.,_r--...__ •.
,
:~'
•
1
•
1
•
~
I,
w 60
o
z
-<
~ 40
~
(/)
~ 20
a:
t-
LlQUID GAS
oL--L_______
4000
0
4000 300
3000
FIG.
FIG. 4.
4.
~
________ L_______ _______ ____
2000 lou 1500
-WW
u 100
WAVE NUMBER
NUMBE RWAVE
~~~~--~~--~~
- cm"
cm-'I
1000
0 9 0900
0 80 800
0 70
0
700
Infrare d spectrum
spectr um of
of SiF4.4CH30H
SiF 4. 4CH 30H and
Infrared
and its
its gaseous
gaseou s products.
produc ts.
gaseous products
products do
do not
not contain
conta in aa strong
gaseous
stron g band
band in
in th^^
this rpainn
regioni^h^
, the ^^
compilex •is not octahedra
lly bonded
bonded and
and therefore
therefore structure
hedrally
^ ' ' " " " ' "'^^^struc ture IIIi t sis not
not valid
valid.
As
shown
in Table
Table II,
II, the
the infrared
infrar ed spectrum
spect rum of
As shown in
ou
of the
the gaseous
gaseo us oroducts
produ cts of
of SiR
SiFirv,
4.4CH 30H
con tains the bands chara cteris tic of gaseous meth anol and silicon
tetraf l uorid e, toget her
with bands of medium inten sity at 1220, 1170, and 930 cm-l. Thes
e band s are chara cteristic of dimethyl ether (16), which is formed in small amou nts by dehy
dratio n of meth anol
with silicon tetrafluoride as cataly st. The fact that the 3680 cm-1
band , ident ified as the
bondstretching
stretchingvibration
bond
- H Ironn
^^"'^^
identified
as the
vibra tionof
ofthe
thefree
freeOO-H
groupu, occur s in the
same positi
on as in gaseo
us
methanol
k t l eor^ fno
T 'hydro
^ gen
' ' ?bond
* ' '^"^^
P-^^'^'^"
^^
in
gaseous
methanol indicates
indicates that
that there
there was
was Ilittle
ing betwe en meth anol and
silicon tetrafluoride
tetrafluoride in
silicon
" e aat
t T10
o l mm
' " 'press
" ' ure.
" " ' A^ furth
'^^^'^^^
"^^^hanol and
in the
the gaseou
gaseous pphase
er indic
ation of the
a~sence of
of "heavy"
"heav y" molecuL
absence
e low
T T ular
" "^
^"'"'^^^
'
"
^
'
^
^
t ' ^ " gaseo
°f the
molecularspecies
specieswas
was Athe
low
molec
weigh t, 57.5,
57.5,of
of the
the
us
mixture.
P " " " ' ^=^^ the low molecular weight,
gaseous
mIxture.
Gl;ERTI~
G
U E R T I N AND ONYSZCHUK: SiF~-CHIOH
SiF<-CH,0H INTERACTION
INTERACTION
1481
TABLE II
l
)
Comparison
Comparison and assignment
assignment of infrared
infrared absorption
absorption frequencies
frequencies (cm(cm~0
SiF
SiF4.4CH30H
4 .4CH aOH
Gas
Liquid
3680 w
2970m
2970 m
2870 m
2870m
1220m
1220 m
1170
111
1170m
1140 nl
m
1060 111
m
1030 s
1000 s
930 m
930111
865 vw
782 w
718 w
CH3OH
CHaOH
Gas
Liquid
SiF
SiF44
Gas
3680 w
3300 s
2950 s
2830 s
2600 m
2600m
1450 m
1110 m
nl
1025 s
950 vw
855 w
1450 w
3340 s
2950 s
2840 m
2840m
2500w
2500 w
1460
1120w
1120 w
1120 m
2950 s
2860 111
m
1030 s
1030 s
860 w
835 w
762 w
720 s
1070w
1070 w
1030 s
Assignment
Assignment
,,(O-H),
^^CO—H), free
free
,,(O-H),
p{0—H), H-bonded
,,(C-H),
p(C—H), antisym.
,,(C-H),
PIC—H), sym.
sym.
Combination
Combination
o(CH
^(CHs),
3 ), antisym.
Due to (CH 33)20
)20
impurity
impurity
o(CH
SCCHs),
a), sym.
SiF4,
combination band
SiF
4, combination
,,(Si-F)
j/(Si—F) tetrahedral
tetrahedral
and p{C—0)
,,(C-O)
(CH
(CH3)20
impurity
3 hO impurity
CH3OH
Due to CH
30H
U
nidentified
Unidentified
,,(Si-F)
j/(Si—F) octahedral for
SiF
62 SiFe^-
NOTE: w
NoTi::
\v = weak.
weak, m = medium, s = strong, v = very.
A comparison of the infrared
of
infrared absorption bands of liquid SiF
SiF4.4CH30H
4 .-!CH 30H with those of
liquid
Hquid methanol and gaseous silicon tetrafluoride, also given in Table II, shows the
following noteworthy
noteworthy features.
features, (i) The band at 3300 cmcm'^l in methanol is shifted
shifted 40 cmcm"^1
lower in SiF
SiF4.4CH30H,
that there is stronger
stronger hydrogen bonding in the complex
4.4CH 30H, indicating that
th
an in pure lnethanol.
4.4CH 30H
than
methanol, (ii) The strong and broad band at 1025 cmcm'^l in SiF
SiF4.4CH30H
undoubtedly
band at
undoubtedly includes the C-O
C—O and Si-F
Si—F bond stretching vibrations.
vibrations, (iii) The band
1
720 cmcm~i also occurs in the gaseous spectrum. This band appeared
appeared with almost the same
intensity
pie was washed from the NaCl
N aCI plates, and after
intensity after
after the liquid sam
sample
after the gaseous
sam
pie was ren10ved
N aCI gas celle
band in the
sample
removed from the NaCl
cell. Moreover, the intensity
intensity of this band
gas phase spectrum
spectrum did not change when the sample pressure was doubled. These observations strongly suggest a surface
surface effect
effect involving the formation
formation of a species which absorbs
absorbs
at 720 cm-l.
This
species
must
be
SiF
2formed
by
the
interaction
of
SiF
with
the
NaCI
cm-^
SiFe^"
interaction
SiF44
NaCl
6
plates, as described recently by Heslop et
(17).
et al. (17).
Proton
ProtonMagnetic
MagneticResonance
ResonanceMeasurements
Measurements
The indication
4.4CH 30H is
indication by the infrared
infrared data
data that
that hydrogen bonding in liquid SiF
SiF4.4CH30H
greater
greater than in pure methanol was investigated
investigated further
further by proton magnetic resonance
measurements. Hydrogen
Hydrogen bonding between methanol and the fluorine atoms of silicon
tetrafluoride
polarizability of
of
tetrafluoride should change the electron density and the local magnetic polarizability
the electrons around the hydrogen atom of the OH group and, to a lesser extent, the
hydrogen atoms of the CHa
CH3 group of methanol. These effects
effects were observed
observed (Fig. 5) as
large and small changes in the chemical shifts
shifts (r)
(r) of the OH and CHa
CH3 peaks, respectively.
respectively.
The effect
effect of concentration
concentration of silicon tetrafluoride
tetrafluoride on these shifts
shifts was examined
examined by measurements on silicon tetraftuoride
4/CH aOH in
tetrafluoride - methanol solutions with mole ratios SiF
SiF4/CH30H
the range 0 to 0.4. Solutions with ratios greater
prepared because the
greater than 0.4 were not prepared
the
OF CHEMISTRY.
CHEMISTRY. VOL.
VOL. 41.
41, 1963
1963
CANADIAN
JOU RNAL OF
CANADIA N JOURNAL
1-182
14S2
r-
CCHH3
j
11
PURECCH
0H .PURE
H3OH
.. Sil~·4CH30H
_____
Sii;-4CH30H
ly-
\~
IIIl
IIJI
IIIl
IIJI
IIIl
IIIl
IIIl
...,
HEIGH
I
W
I
PEAK
~
«
w
a.
Il
1!
w
LJ
RELATIV
>
OH
OH
1-
«
..J
w
0:
...
JCH3
:CH3
ll
1
OH
OH
'I
l"|
l|
"
',11
»
•
1/11
CsH s
CeHa
lJlA 1
i1
2.5
2.5
lil
,1
f\1
il
,1
,1
1
~
'I
UL'1
1
3.5 4.
4.5
3.5
5 5.
5.5
5
CHE
MI1CCAL
CO) p.p.m
p.p.m..
C
HEM
A L S HSHI
I F FT
T CT
6.5
6. 5
F IG. 5.
o.
.. Chemical
Chemical shifts
shifts of
of pure
pure methanol
methanol and
and methanol
methano 1 hydrogen
FIG.
tetrafluoride.
h y d rogen bonded
bonded to
to silicon
silicon tetrafluoride.
sealed glass
glass sample
sam pIe tubes
tubes might
might have
have exploded
exploded due
due to
to internal
internaI pressures
pressures in
in the
the tens
tens of
of
sealed
atmospheres.
atmospheres.
is an
an initial
initial linear
linear and
and rapid
rapid decrease
decrease in
in
The plot
plot given
given in
in Fig.
Fig. 6
6 shows
shows that
that there
there is
The
5~----------------------~
Ë
ci.
ci.
4
~
..,
1-
-lJ...
I
3
(/)
..J
«
-u
~
I
U
2
•
I~----~----~----~------~
o
FIG.
FIG. 6.
6.
0.1
0.22 0.
0.33 0.
0.1 0.
MOLE
RATIO
Si~/CH30H
MOLE R A T
I
O~ S\F^/CH^OH
- • • 4
/ V- ' ' 3 ^ " - i
4
Variation
Variation of
of the
the chemical
chemical shift
shift of
of the
the OH
OH peak with
with mole
mole ratio
ratio of
of silicon
silicon tetrafluoride
tetrafluoride to
to methanol.
methanol.
Tvalue
valueofofthe
theOH
OH peak
peakasasthe
theamount
amount of
ofsilicon
silicontetraftuoride
tetrafluoride isisincreased.
increased The
T h . slope
=1^ ( of this
.uline
changes
markedly
near
a
mole
ratio
of
n
9
.nH
fin
I
"^''''^^^'^^
h
e
slope
of
this
line changes markedly near a mole ratio of 0.2 and finally becomes constant and smaller
than initially. A comparison o T ^ h / ^ l i l ^"^ finally becomes constant and smaller
than initialIy. A comparison of the magnitude and direction (from high to low field) of
the
the observed
observed chemical
c h e S l i shifts
L ^ ^ Jwith
i
Tthose
h T eof
' ^ the
o f t methanol
h ^ m t r j - 'carbon
^ b ' Htetrachloride
' " T ' ' ' ' 'and
°^
methanol-chloroform systems
systems (18)
(18) reveals
reveak that
fh,f- (i)
r^ ^^Y'''''°^
7 '^^'^bonOCcurs
tetrachloride
and
methanol-chloroform
hydrogen bonding
to a greater
extent between
between silicon
silicon'tetrTfluorlandte^^^^^^^^^^
^-^^^er
extent
tetraftuoride and methanol '°(,h", 3.5 p.p.m.) than in ^methanol
alone (IlT'"
(A. ~ 3.0
3.0 p.p.m.);
p.p.m.); (ii)
(.i) successive
successive addition
a d T i L Tof
o / silicon
i h c r n tetraftuoride
tft"'^^^
''^^"«'
alone
does' "not' " ^simply
. l u t e the
. e methanol;
methanol; ifif itit did,
did. the
the chemical
chemical shift
^ ^would
^ ^ be: towards
: : : higher
^ : ^ magnetic
^ : ^ £
dilute
field^
strength.
T
Our
Our interpretation
interpretation of
of Fig.
P i , 6e isis as
as follows.
follows. The
The chemical
chemical shift
shift of
of the
the OH
OH peak
peak of
of pure
pure
GUERTI)J
G U E R T I N A?\D
A N D ONYSZCHUK: SiF4-CHaOH
SiF4-CH30H INTERACTION
INTERACTION
1483
1483
methanol (T
of
(r == 4.712 p.p.m.) decreases upon the successive addition of small amounts of
silicon tetrafluoride
4. 4 CH aOH molecular
tetrafluoride because of the immediate formation
formation of SiF
SiF4.4CH30H
species and rapid exchange between solvent methanol and methanol hydrogen bonded to
silicon tetrafluoride. In order to observe the OH peaks of both types of methanol simullifetime of each state must be longer than the reciprocal of the chemical shift
shift
taneously the lifetillle
(in cycles/sec) between
between the two states (19). Thus, the single OH peak observed at each
SiF4/CH30H
mole ratio was
\vas an average value. These values decreased as the mole ratio SiF
4/CH aOH
that proportionately
methanol was hydrogen bonded to silicon
increased, indicating that
proportionately more Inethanol
all of the methanol was used up in the formation
formation
tetrafluoride. When
\\~hen the ratio became 0.25 aIl
SiF4.4CH30H
complex. Further
Further addition of silicon tetrafluoride
tetrafluoride produced
secondary
of the SiF
4.4CHaOH complexe
produced secondary
concentration effects
effects which
SiF4/CH30H.
concentration
\vhich were directly proportional
proportional to the mole ratio SiF
4/CH aOH.
CH3 peak (Fig. 7) decreased gradually
gradually and finally levelled off
off as
The TT values of the CHa
E
7
Ë7~----------------------~
<i.
'"
E
1-
L.r....
i6
X6
Vl
10
•
—
•
—
—
—
*
••
*
—
•
m"
,
...J
<
u
:E
u
50
l
0.1
0.2
0.3
X
3 0.0H
U 0 0. MOLE 1 0.RATIO2 0.
SiF4 /CH
3
^ MOL
E RATI
O SiF./CHjO H
WsL-----L-----~----~----~
0.4
4
FIG. 7. Variation of the chetnical
chemical shift
shift of the CHa
CH3 peak with
tetrafluoride to
FIG.
\Vith the mole ratio of silicon tetrafluoride
methanol.
the concentration
concentration of silicon tetrafluoride
tetrafluoride increased. The decrease was not large because
the protons of the CHa
CH3 group were observing only secondary
secondary effects.
effects.
Structure ofof SipA-'iCHzOH
Structure
SiF 4 .-'T-CHaOH
The experimental
experimental data
data reveals that
that the complex in the liquid or solid state (i) has the
composition
4.4CH aOH, (ii) is only very slightly dissociated into ions
composition represented
represented by SiF
SiF4.4CH30H,
in methanol, (iii) does not contain
contain Si-O
Si—O bonds, (iv) contains stron?"
strong hydrogen bon?s.
bonds.
The most reasonable explanation
of
these
data
is
that
the
complex
IS
tetrahedral
explanation
data
that
is tetrahedral wlth
with
strong hydrogen
bonds
between
methanol
and
each
of
the
four
fluorine
atoms
(III).
hydrogen
between
fluorine
(HI).
HOCH,
~OCH3
F
/
1
I/~\
4
1\ \
/J* ^
Si' \
1 / / ~~F.".'HOCH
F HOCH.3
CH
CH^OH'
:.3OH····.. F~-- __ ',/
t,
f
HOCH.
~OCH3
nr
:nI
EXPERIMENTAL
Most
standard pyrex-gla~s
pyrex-gh^^^^^^
~10st of the materials used in this work were manipulated in a standard
high-vacu~m.~ystem
which had stopcocks and ground-glass joints lubricated
lubricated with Kel-F grease.
grea e Tlhe
The P
^
J
^
J
^ ^h^ vo
Tnd~t~ nfrarTd
pu:Ithy ^of(Mth)e
e comci
.
d
b
nts
of
their
vapor
pressures,
molecu
ar
welg
ts
,an
ln frare
pounds
was
d
L
r
m
i
n
e
d
by
measurements
of
the^r
vapo^
p
r
pounds was determlne
y measureme
. -El
Infracord double-beam spectrophotometer
Infrared spectra were recorded on a Perkln
Perkm-Elmer
spectra. Infrared
mer iniracora uuuu
equipped with sodium chloride optics.
equipped
1484
CANADIAN JOURNAL OF CHEMISTRY. VOL.
VOL. 41.
41. 1963
methanol was obtained
obtained by
refluxing for a few hours 50 ml of
of the
material
Anhydrous methanol
by refluxing
th~ commercial
com.me~cial grade material
over about
been add~d.
about 1 g of freshly
freshly cleaned Mg turnings to which a few crystals of resubhmed
resublimed lOdlne
iodine had
had been
added.
The distillate boiling at
~he :racuum
at 63-64° was collected
collected and redistilled
redistilled at
a t -23°
- 2 3 ° i.n
in the
vacuum system. CommercIal
Commercial
tetrafluoride was purified
low-temperature vacuum
vacuum dlstlllatlOns.
distillations.
silicon tetrafluoride
purified by
by several low-temperature
Preparation
Preparationofof SiF\.4CHzOH
SiF4 .4CH30H
. . '
In a typical experiment
experiment SiF
SiF44 (10.48 mmole) was combmed
combined ln
in a vacuum
vacuum wtth
with ~ethanol
methanol (8.44,.mmole),
(8.44 mmole),
and the mixture was kept
nreacted SlF
kept at
at 25° for 30 minutes and
and finally
finally cooled slowly to -115
—115°... U
Unreacted
SiF44 (8.32
by distillation
SlF 4 (2.16 mmole) had
mmole) was recovered
recovered by
distillation first
first at
a t -115°
- 1 1 5 ° and
and then at
a t -65°.
- 6 5 ° . Therefore,
Therefore, S\¥^
had
reacted
producing the complex
4 .4CH 3 0H. Infrared
reacted with CH
CH3OH
complex SiF
SiF4.4CH30H.
Infrared
30H (8.44 mmole) in a mole ratio of 1:3.91, producing
and
and molecular
molecular weight measurements
measurements showed that
t h a t the gas phase in equilibrium
equilibrium with the liquid at
a t 25° consisted of SiF
4 : M, 104.1.)
SiF44 and CH
CH3OH.
CH3OH:
32.1; for SiF
SiF4:
104.1.)
30H: M, 32.1;
30H. (Found: M, 57.5. Calc. for CH
Tensimetr1~cTitrations
Titrations
Tensimetric
Preliminary
Preliminary experiments
experiments indicated
indicated that
t h a t -78°
—78° was a suitable temperature
temperature at
a t which to measure total
total
pressures in the tensimetric titration
titration of SiF
SiF44 with CH
CH3OH.
temperature
complex
measurably
0H.
At
this
temperature
the
complex
is
not
measurably
3
dissociated and any excess SiF
SiF44 (b.p.
(b.p, -94.8°)
—94.8°) would be entirely
entirely in the gaseous phase. Measured
Measured amounts
a m o u n t s of
of
dissociated
methanol were added in successive small amounts (about
(about 2 mmole at
a t a time) to a fixed
fixed quantity
q u a n t i t y of SiF
SiF44
methanol
After each addition
addition the mixture was warmed
warmed to 25° for about
about 15 minutes before
slowly
before it was slowly
(5.43 mmole). After
—78°, at
a t which temperature
temperature pressure measurements
measurements were made. A plot
against
plot of total pressure
pressure against
cooled to -78°,
CH3OH
SiF44 is shown in Fig. 1. The reverse titration
titration of CH
CH3OH
addition of SiF
SiF44 gave
gave
mole ratio of CH
by addition
30H to SiF
30H by
the results shown in Fig. 2.
Conductivity ofof SiFi.4CHzOH
Conductivity
SiF4 .J,.CH30H
Conductivity
Conductivity measurements
measurements were made using a conductivity
conductivity bridge (Industrial
(Industrial Instruments
I n s t r u m e n t s Model
Model
R C 16 B2) and
and a cell having a cell constant
constant of 0.01. The
T h e instrument
instrument had a conductivity
conductivity range of 4
4X10~^
RC
X 10-9 to
5X10~22 mho cm-l.
cm~^ Transfer
Transfer of solutions and measurements
measurements were made in a nitrogen-filled
nitrogen-filled dry
dry box to avoid
avoid
5X10concentration of SiF
SiF4.4CH30H
Table I)
I)
hydrolysis by atmospheric moisture. A sample with the highest concentration
4.4CH 30H (see Table
vacuum system
system and then transferred
transferred to the conductivity
conductivity cell in the dry box, and
a n d its
was prepared
prepared in the vacuum
conductivity was measured. Solutions of lower concentration
concentration were prepared
conductivity
prepared by
by successive dilutions with
methanol.
ProtonMagnetic
MagneticResonance
ResonanceMeasurements
lJleasurements
Proton
Proton
Proton n.m.r. spectra
spectra were recorded on a high-resolution
high-resolution Varian
Varian spectrometer
spectrometer with a fixed
fixed frequency
frequency
of 60 Mc. Pure benzene contained
contained in a sealed capillary
capillary was used as the external
external standard
standard (T
(r = 2.734 p.p.m.).
It was placed in a pyrex glass tube, 17 cm long and
and 5 mm outside diameter, into which solutions of known
known
It
SiF44 to CH
CH3OH
T h e sample tube was sealed off
off in a vacuum
vacuum at
a t a constriction.
constriction.
30H were condensed. The
mole ratio of SiF
The results are shown in Figs. 5, 6, and 7.
ACKNO\VLEDGMENTS
ACKNOWLEDGMENTS
We thank
thank the
the National
Research Council
Council for
for financial
financial assistance
assistance in
in the
the form
form of
of an
an annual
annual
We
National Research
grant (to M. O.). We are grateful
grateful to Dr. J. T. Edward for many helpful
helpful discussions and to
Stammer for the n.m.r. measurements.
Dr. A. Taurins and Dr. C. Stammer
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