M agnetic Properties o f Som e D ivalent
Transition M etal Cupferron Complexes
A . H . A b o u E l E la a n d H . H . A f if i
Physics Department, National Research Centre Cairo, Egypt
(Z. N aturforsch. 29b, 52 4 -5 2 6 [1974]; received A pril 30, 1974)
Magnetic moments, Cupferron complexes, Copper
The magnetic susceptibilities and magnetic moments of the ammonium salt of cupferron
and manganese, cobalt, nickel and copper divalent complexes are investigated. The ammo­
nium salt of cupferron is diamagnetic while the divalent transition metal cupferron
complexes exhibit paramagnetic behaviour. For manganese, cobalt and nickel cupferrates the magnetic moment is smaller than the spin-only value, which reflects the effect
of the orbital angular momentum and electron delocalization. For copper cupferrate
the magnetic moment is nearly equal to the spin-only value.
The m agnetic properties of tran sitio n m etal
complexes are of in terest since specific inform ation
ab o u t th e electronic structure of these complexes
could be obtained from m agnetic m easurem ents.
C upferron is a well know n chelating agent. YoSHIMTJBA1, studied th e I R and UV spectra of cupfer­
ron and neocupferron. Recently, detailed analysis
of th e IR and UV spectra of cupferron and some
divalent tran sitio n cupferron complexes were re ­
p o rte d 2-4. The electronic structures of these com­
plexes were studied from the absorption spectro­
scopy point of view. A tetrah ed ral crystal field wras
suggested for th e divalent transition m etal com plex­
es investigated.
The present contribution is aim ed to investigate
the m agnetic properties of th e am m onium salt of
cupferron and some divalent tran sitio n cupferrate
complexes. The results obtained are in terpreted on
the basis of ligand field theory.
Experimental
All chemicals used were A. R. grade, B. D. H.
label. The am m onium salt of cupferron was ob­
tain ed from H un g ary “ Reanal, finomvegyszergyar,
B u d ap est.” The different cupferrate complexes
were prepared by th e m ethod described earlier2.
E lem ental chemical analysis for th e m etal com­
plexes prepared gave a chemical composition of
Requests for reprints should be sent to Dr. A . H.
Semiconductor Research Lab., National
Research Centre El Dokki, El Tahrir Street. C airo ,
U .A . R.
A b o u E l E la ,
ML.,, where M stands for the m etal (Mn, Co, Ni and
copper) an d L for the ligand (C6H 50 2N 2).
The Gouy m ethod has been used for the com­
pounds investigated in th e powder form. M easure­
m ents were carried out in quartz ampoules, each
am poule wras suspended so th a t th e lower end of
th e sam ple wras in th e center of a homogenous
m agnetic field. M oreover, the am poule was sym ­
m etrical w ith respect to th e polepieces of the
m agnet and consequently, th e interactions of the
upper and lowrer half of th e am poule w ith the m ag­
netic field were m u tually com pensated. The mean
susceptibility wras m easured for th e compounds.
Corrections for th e porosity of th e powder inside
th e specimen tu b e was applied. Different m agnetic
field intensities were used and the diam agnetic
correction for th e ligand wras considered. Pure
distilled w ater wras used as a standard. Its suscepti­
bility a t t [ÜC] is given dy
yw = _ [0.72145 + 0.000108 (t - 20)] 10“6 s.g.s.e.
m.u.
Results and Discussion
The m ean values of the m agnetic m om ents of the
different complexes is shown in Table I. The results
are com pared w ith the spin-only m agnetic m om ent
calculated for the ions considered5. All the tra n si­
tion m etal cupferron complexes show param agnetic
behaviour. The m agnetic m om ent, determ ined
experim entally, is sm aller th a n th e spin-only
m agnetic m om ent /us-°■ = S (S + 1)1/2, only in the
case of copper cupferrate th e m agnetic m om ent
obtained (1.76 B.M) is nearly equal to the spin-only
value (1.73 B.M.).
F i g g i s 5 showrs, th a t there is likely to be a loss of
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A. H. ABOU EL ELA -H . H. A FIFI • MAGNETIC PR O PER TIES OF CUPFERRON COMPLEXES 525
Table I. The magnetic moments of cupferron and some divalent transition metal cupferron complexes.
Compound
Ion
Ground term
No. of unpaired Magnetic
d electrons
moment meas­
ured [B.M.]
M n2+
Co2+
N i2+
6Ai(S)
4A 2 (F)
3T, (F)
Cu2+
2T 2 (D)
5
3
2
1
Magnetic
moment spinonly calculated
[B.M.]
-0.382
Cupferron
Mn (Cup.)2
Co (Cup.)2
Ni (Cup.),
Cu (Cup.)2
orbital angu lar m om entum upon the incorporation
of th e free ion into a complex. For complexes w ith
A and E ground term s th e orbital angular m o­
m entum is quenched, while it m ay exist for com­
plexes w ith T 2 and T 2 ground term s. In sp ite of
these facts th e m agnetic m om ents of complexes
w ith A an d E ground term s usually differ appreci­
ably from th e spin-only value to which th e y are
expected to conform in th e absence of orbital angu­
lar m om entum in the ground term . The reason for
d ep artu re from th e spin-only value lies p a rtly in
th e existence of the second order Zeem an effect
betw een th e ground and th e higher ligand field
term s. H ow ever, it lies m ainly in the fact th a t, in
th e presence of spin-orbit coupling, th e quenching
effect of th e ligand field cannot be complete. T here­
fore, th e m agnetic susceptibility of complexes
possessing A and E ground term s should be a Curie
law dependence plus a sm all constant te rm (tem per­
atu re independent param agnetism T .I.P .).
F or com plexes w ith 6A 1 ground term (M n2+) the
m agnetic m om ent should equal to th e spin-only
value (according to ligand field theory) while the
T .I .P is zero. The value m easured for th e m agnetic
m om ent of M n2+ in m anganese cupferrate (4.92
B.M .) is sm aller th an the calculated value for spinonly m om ent which contradicts the theoretical
conclusions. The difference could be a ttrib u te d to
th e effect of residual orbital angular m om entum or
to th e occurence of a disto rtio n in the crystal field.
F or C o2+ complexes w ith 4A2 ground term the
m agnetic m om ent from th e first order Zeeman
effect an d th e T .I .P susceptibility are given b y 5’6
^eff
s.o. / i
elf
(
4 k~ Aq
110 Dq| ),
8 k 2 ~Nß
Z t .i . p —
110 Dqi
4.92
3.4
5.92
3.87
2.32
2.83
1.73
1.76
where / 0 = ± ^ is th e spin-orbit coupling p a ra ­
m eter, £ is th e single electron spin-orbit coupling
constant, 10 D q is th e separation betw een the e and
t 2 orbitals, k is a factor which accounts for th e re­
duction of th e orbital angular m om entum of a
m etal ion consequent upon th e delocalization of
electrons out of th e t 2 orbitals of the ion onto the
ligand atom s to form th e m olecular orbitals of the
complex, N and ß are A vogadro’s num ber and Bohr
M agneton.
The difference betw een th e value obtained for the
m agnetic m om ent of Co2+ in cobalt cupferrate
(3.4 B.M .) and th e spin-only value (jus-°- = 3.87) is
evidence of a sm all degree of electron delocalization.
O ptical absorption m easurem ents3’4 shows th a t the
tran sitio n 4A2 (F) —> 4T 1 (P) in cobalt cupferrate
occurs around 16000 cm -1, therefore applying
TANABE-SUGANO diagram s7 a value for [10 Dq|
~ 3530 cm-1 is obtained. Using the above m entioned
relations, the value obtained for the “ orbital re ­
du c tio n ” or “delocalization” factor is k ~ 0.75. The
L a n d e splitting factor could be also obtained from
th e relation
4 k- /.o
2 (1
110 Dq|
~ 2.218
Therefore, th e reduction observed in the room
tem p eratu re m agnetic m om ent does n ot arise
principally from an increase in th e splitting of the
orbital q u artet even when appreciable distortion
is to be expected, b u t th e m ain factor seems to be a
decrease in th e value of th e electron delocalization
param eter k.
The difference betw een the m easured value of
th e m agnetic m om ent for N i2+ in nickel cupferrate
(2.32 B.M .) and th e spin-only value (2.83 B.M.)
could be a ttrib u te d to a small electron delocalization
effect. From optical absorption d a ta 3-4 three
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526 A. H. ABOU EL ELA -H . H. A F IF I • MAGNETIC PR O PER TIES OF CUPFERRON COMPLEXES
absorption bands were observed a t 625 nm , 641 nm
and 700 nm w ith th e center of g rav ity ~ 15300 cm-1.
These bands represents a single tran sitio n , 3T 4 (F) —>
3Tj (P), split by either spin-coupling m echanism or
a low sym m etry ligand field. Using TANABESUGANO diagram s a value of |10D q| ~ 2200 cm-1
is obtained. A pproxim ate calculations shows, th a t
the ligand field param eter A is about 1.35, th e re­
fore, the crystal field m ay be considered to be a
m edium one (for weak field A = 1.5 and for strong
field A = 1).
M easurem ents of the m agnetic m om ent of C u2+
in copper cupferrate give a value /u = 1.76 B.M.,
which is nearly equal to th e spin-only value (1.73
B.M.). This result shows a strong reduction of
orbital angular m om entum . The m agnetic suscep­
tibility could be described by a model in w hich the
system is an ensemble of S = 7 2 units each w ith a
ground-state singlet and excited triplet obeying
B oltzm ann statistics
1 T. Y o s h i m u r a , C. M i y a k e , a n d S. I m o t o , B u l l ,
chem. Soc. J a p . 45, 5, 1424 [1972].
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[1973].
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4 A . H. A b o u E l E l a a n d H. H. A f i f i , Z. N a t u r f o r s c h . 29a, [1974].
5 B . N. F i g g i s , Introduction to Ligand Fields, Inter­
science Publishers, New York 1966.
6 B. N. F i g g i s , M . G e r b a c h , and R. M a s o n , Proc.
Roy. Soc. A 2 7 9 . 210 [1964],
7 Y. T a n a b e and S . S u g a n o , J. c h e m . S o c . Jap. 9, 753
[1954],
8 G . J. M a a s , B. C. G e r s t e i n , and R. D. W i l l e t , J.
chem. Physics. 46, 401 [1967].
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J. appl. Physics 43, 1932 [1972].
1
x
-
1 + 1
Ae
small T .I .P
PKT
where As is the singlet-triplet separation. A pproxi­
m ate calculations show, th a t th e value of th e a c tiv ­
ation energy Ae for Cu2+ in copper cupferrate is
~ 0.04 eV. The g factor could be calculated from
th e experim ental d a ta in the Curie-Wiess range
using th e spin-only form ula9
N g 2^2
X =
3 k •T
S (S + 1) (with S = 7 2
a value of g = 1.932 was obtained.
The authors wish to thank Dr. H. F. A l y for previ­
ous discussion on the preparation of the complexes.
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