Thermal, spectral and magnetic characterization of Co(II), Ni(II) and Cu(II) 4-chloro-2-nitrobenzoates

Article abstract of DOI:10.1007/s10973-005-7318-z

Physico-chemical properties of 4-chloro-2-nitrobenzoates of Co(II), Ni(II), and Cu(II) were studied. The complexes were obtained as mono- and trihydrates with a metal ion to ligand ratio of 1:2. All analysed 4-chloro-2-nitrobenzoates are polycrystalline compounds with colours depending on the central ions: pink for Co(II), green for Ni(II), and blue for Cu(II) complexes. Their thermal decomposition was studied only in the range of 293-523 K, because it was found that on heating in air above 523 K 4-chloro-2-nitrobenzoates decompose explosively. Hydrated complexes lose crystallization water molecules in one step and anhydrous compounds are formed. The final products of their decomposition are the oxides of the respective transition metals. From the results it appears that during dehydration process no transformation of nitro group to nitrite takes place. The solubilities of analysed complexes in water at 293 K are of the order of 10^-4-10^-2 mol dm^-3. The magnetic moment values of Co²⁺, Ni²⁺ and Cu²⁺ ions in 4-chloro-2-nitrobenzoates experimentally determined at 76-303 K change from 3.89 to 4.82 μ_B for Co(II) complex, from 2.25 to 2.98 μ_B for Ni(II) 4-chloro-2-nitrobenzoate, and from 0.27 to 1.44 μ_B for Cu(II) complex. 4-chloro-2-nitrobenzoates of Co(II), and Ni(II) follow the Curie-Weiss law. Complex of Cu(II) forms dimer.

Full text of DOI:10.1007/s10973-005-7318-z

Journal of Thermal Analysis and Calorimetry, Vol. 86 (2006) 2, 359–364
THERMAL, SPECTRAL AND MAGNETIC CHARACTERIZATION OF
Co(II), Ni(II) AND Cu(II) 4-CHLORO-2-NITROBENZOATES
1
*
1
WiesÓawa Ferenc , Agnieszka Walków-Dziewulska , Maria Wojciechowska and J. SarzyÕski
1
2
1
Faculty of Chemistry, Maria Curie-SkÓodowska University, 20-031 Lublin, Poland
Institute of Physics, Maria Curie-SkÓodowska University, 20-031 Lublin, Poland
2
Physico-chemical properties of 4-chloro-2-nitrobenzoates of Co(II), Ni(II), and Cu(II) were studied. The complexes were obtained
as mono- and trihydrates with a metal ion to ligand ratio of 1:2. All analysed 4-chloro-2-nitrobenzoates are polycrystalline com-
pounds with colours depending on the central ions: pink for Co(II), green for Ni(II), and blue for Cu(II) complexes. Their thermal
decomposition was studied only in the range of 293–523 K, because it was found that on heating in air above 523 K
4-chloro-2-nitrobenzoates decompose explosively. Hydrated complexes lose crystallization water molecules in one step and anhy-
drous compounds are formed. The final products of their decomposition are the oxides of the respective transition metals. From the
results it appears that during dehydration process no transformation of nitro group to nitrite takes place. The solubilities of analysed
–
4
–2
–3
2+
2+
2+
complexes in water at 293 K are of the order of 10 –10 mol dm . The magnetic moment values of Co , Ni and Cu ions in
4-chloro-2-nitrobenzoates experimentally determined at 76–303 K change from 3.89 to 4.82 m
B
for Co(II) complex, from 2.25 to
2
.98 m for Ni(II) 4-chloro-2-nitrobenzoate, and from 0.27 to 1.44 m for Cu(II) complex. 4-chloro-2-nitrobenzoates of Co(II), and
B
B
Ni(II) follow the Curie–Weiss law. Complex of Cu(II) forms dimer.
Keywords: 4-chloro-2-nitrobenzoates, complexes of Co(II), Ni(II) and Cu(II), IR spectra, magnetic moments, thermal stability
Introduction
investigations give informations about the process of
dehydration. The magnetic susceptibility measure-
ments let study the kinds of the way of coordination of
the central ions, and the nature of the bonding between
central ions, and ligands. If the magnetic moment is
known, the number of unpaired electrons can be calcu-
lated. This may also give information on the oxidation
state of the central metal ion of a complex. When the
number of unpaired electrons on the ion of complex is
known the spin-only moment can be calculated. The
deviation of the measured magnetic moment from the
spin-only permits the drawing of conclusion on the
symmetry of the complex in certain cases. The deter-
mination of the number of unpaired electrons on the
central atom establishes whether the complex investi-
gated is of low or high spin or the ligands form the
strong or weak fields.
4-Chloro-2-nitrobenzoic acid is a light-yellow crystal-
line solid sparingly soluble in water. Its electrolytic
dissociation constant is equal to 1.0·10 (25°C) and
melting point 140°C [1]. The compounds of 4-chloro-
–2
2-nitrobenzoic acid anion are very little known. A sur-
vey of the literature shows that it is possible to find pa-
pers on the complexes of various ligands with some of
d block elements [2–7] and also on their salts with
4
-chloro-2-nitrobenzoic acid anion. The salts of
-chloro-2-nitrobenzoic acid anion were obtained in
4
the solid state only with the cations: NH , Na , K ,
+
+
+
4
+
2+
2+
2+
Ag , Cu , Ca , Ba , and with rare-earth elements
1, 8]. 4-chloro-2-nitrobenzoate of Cu(II) was obtained
in the solid state as trihydrate with light-green colour
1]. Moreover some complexes of transition element
[
[
cations with various isomers of chloronitro- and
chloromethoxybenzoic acid anions were also prepared
as solids and investigated [8–15]. The 4-chloro-2-
nitrobenzoates of Co(II) and Ni(II) have not been ob-
tained so far. Therefore the aim of this work was to
prepare them in the solid state, and also that of Cu(II),
and to examine some of their physico-chemical proper-
ties including thermal stability in air during heating to
Experimental
The 4-chloro-2-nitrobenzoates of Co(II), Ni(II) and
Cu(II) were prepared by adding the equivalent quanti-
ties of 0.1 M ammonium 4-chloro-2-nitrobenzoate
(pH»5) to a hot solution containing the Co(II), Ni(II)
and Cu(II) chlorides and crystallizing at 293 K. The
solids formed were filtered off, washed with hot water
and methanol to remove ammonium ions, and dried at
523 K, IR spectral characterization, X-ray powder in-
vestigations, solubility in water at room temperature,
and magnetic behaviour at 76–303 K. Thermal stability
*
Author for correspondence: wetafer@hermes.umcs.lublin.pl
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2006 Akadémiai Kiadó, Budapest

FERENC et al.
3
03 K to a constant mass. The contents of carbon, hy-
The solubilities of 4-chloro-2-nitrobenzoates of
Co(II), Ni(II) and Cu(II) in water were measured at
293 K. Saturated solutions of the obtained com-
pounds were prepared under isothermal conditions.
The contents of Co(II), Ni(II) and Cu(II) were deter-
mined using ASA 880 spectrophotometer (Varian).
Magnetic susceptibilities of polycrystalline sam-
ples of 4-chloro-2-nitrobenzoates of Co(II), Ni(II)
and Cu(II) were investigated at 76–303 K. The mea-
surements were carried out using the Gouy method
with magnetic field strength of 9.9 k0e. Mass changes
were obtained from Cahn RM-2 electrobalance. The
drogen and nitrogen were determined by elemental
analysis using a CHN 2400 Perkin Elmer analyzer.
The content of chloride was determined by the
Schöniger method. The contents of metals were estab-
lished by ASA method with the use of ASA 880
spectrophotometer (Varian).
The IR spectra of complexes were recorded over
–
1
the range 4000–400 cm using M-80 spectrophoto-
meter (Carl Zeiss, Jena). Samples for IR spectra mea-
surements were prepared as KBr discs.
The X-ray powder diffraction patterns were per-
formed on a HZG-4 (Carl Zeiss, Jena) diffractometer
using Ni filtered CuK radiation. The measurements
were made within the range of 2q=4–80° by means of
the Debye–Scherrer–Hull method.
The thermal stability and decomposition of the
complexes were studied in air using a Setsys 16/18
TG, DTG and DSC instrument. The experiments were
carried out under air flow in the temperature range of
calibrant employed was Hg[Co(SCN) ] for which the
4
magnetic susceptibilities was assumed to be
a
–
5
3
–1
1.644·10 cm g . Correction for diamagnetism of
the constituent atoms was calculated by the use of
Pascal’s constants [16, 17]. Magnetic moments were
calculated according to Eq. (1):
1
/2
µ =2.83(c T)
eff M
(1)
2
5
93–523 K. Samples ranging from 5.19 mg (Co),
.18 mg (Cu) to 5.06 mg (Ni) were heated in Al O
3
2
Results and discussion
crucibles.
The thermal stability and decompositions of the
prepared chloronitrobenzoates were determined by
Paulik–Paulik–Erdey q-1500D derivatograph with
Derill converter, recording TG, DTG and DTA
curves. The measurements were made at a heating
4
-Chloro-2-nitrobenzoates of Co(II), Ni(II) and
Cu(II) were obtained as polycrystalline solids with a
metal ion to ligand ratio of 1:2, and general formula
M(C H O NCl) ·nH O (where M=Co, Ni, Cu, and
n=3 for Co and Ni, n=1 for Cu), and colours: pink for
Co(II), green for Ni(II) and blue for Cu(II) complexes
7
3
4
2
2
–
1
rate of 10 K min with a full scale. The samples
100 mg) were heated in platinum crucibles in static
(
(
Table 1).
Some of the results of IR spectra analysis are in
air to 523 K with a TG sensitivity equal to 100 mg.
DTG and DTA sensitivities were regulated by com-
puter Derill programme. The products of decomposi-
tion were calculated from TG curves and verified by
the X-ray diffraction pattern.
Table 2. The infrared spectrum of 4-chloro-2-nitro-
benzoic acid shows the following absorption bands
–
1
18–21]: a strong band of COOH at 1710 cm , the
[
bands assigned to asymmetric and symmetric vibra-
–
tions of NO group at 1530 and 1350 cm , the bands
1
2
Table 1 Elemental analysis data of Co(II), Ni(II) and Cu(II) 4-chloro-2-nitrobenzoates
Complex
H/% C/% Cl/%
N/%
M/%
–
7 3 4
L =C H O NCl
calcd
2.33
2.34
1.66
found
2.35
2.48
1.51
calcd
32.68
32.70
34.81
found
32.33
32.19
34.87
calcd
13.80
13.82
14.71
found
13.80
13.84
14.71
calcd
5.45
5.45
5.80
found
5.30
5.40
5.78
calcd
11.46
11.42
13.16
found
11.40
11.30
13.10
CoL
NiL
Cu
2
·3H
·3H
·2H
2
O
2
2
O
2
L
4
2
O
–
1
–
Table 2 Wavenumbers (cm ) of COO bands in 4-chloro-2-nitrobenzoates of Co(II), Ni(II), Cu(II) and Na(I) and of the COOH
band in 4-chloro-2-nitrobenzoic acid
Complex
n
C=O
n
asOCO
n
SOCO
DnOCO
n
C–Cl
n
M–O
–
L =C
CoL ·3H
NiL ·3H
Cu ·2H
HL
7
H
3
O
4
NCl
2
2
O
–
–
–
1590
1590
1620
–
1400
1400
1420
–
190
190
200
–
740
740
750
–
500
490
540
–
2
2
O
2
L
4
2
O
1710
–
NaL
1625
1400
225
760
440
360
J. Therm. Anal. Cal., 86, 2006

Co(II), Ni(II) AND Cu(II) 4-CHLORO-2-NITROBENZOATES
–
1
of nC–C vibrations at 1610, 1425, 1150 and 1110 cm ,
the bands of n vibrations at 3100, 900 and
analogues in the endothermic process [24]. It was
found that the isomerization of the nitro group may
accompany the dehydration process of the complex or
be connected with the transformation process in its in-
ner sphere [25]. As a monodentate ligand, nitrite ion
may be bounded either through a nitrogen atom form-
ing the nitro complex or through one of the oxygen at-
oms yielding a nitrite complex. The general effect of
coordination via nitrogen is a rise in the frequencies
of both nas(NO 2 ) and ns(NO 2 ) compared to the values for
the free ion ~1328 and ~1260 cm , respectively [26].
The IR spectra recorded for the hydrated, and dehy-
drated 4-chloro-2-nitrobenzoates of Co(II), Ni(II) and
Cu(II) show that the nitro group is not transformed to
the nitrite group with rising temperature. No bands
confirming the isomerization of the nitro group
through the oxygen atom are observed [25, 26].
From the X-ray diffraction patterns recorded for
the 4-chloro-2-nitrobenzoates of Co(II), Ni(II) and
Cu(II) it appears that they are crystalline of low sym-
metry and large size of the unit cells. They have dif-
ferent crystal structures [27], which have not been de-
termined, because their single crystals have not been
obtained so far.
It follows from earlier studies on the thermal sta-
bility of 4-chloro-2-nitrobenzoates of Co(II), Ni(II)
and Cu(II) that on heating these complexes are explo-
sively decomposed when heated above 523 K [28, 29].
The thermal stability of 4-chloro-2-nitrobenzoates of
Co(II), Ni(II) and Cu(II) was studied in the range of
293–523 K. The results reveal that the analysed com-
pounds lose the crystallization water in one step at
347–395 K. The process is connected with an endo-
thermic effect as shown by the DTA curves [30–32].
The anhydrous 4-chloro-2-nitrobenzoates are
formed above 380 K. The loss in mass calculated
from TG curves is about 11% in the case of tri-
hydrates, and 4% in the case of monohydrate of Cu(II)
4-chloro-2-nitrobenzoate (Table 3). Their theoretical
values are 10.5 and 3.7%, respectively. Considering
the temperatures at which the dehydration takes place
and the way by which it proceeds it is possible to as-
sume that the water molecules form outer sphere wa-
ter [32]. The anhydrous complexes of Co(II), Ni(II)
and Cu(II) are finally decomposed to the oxides of re-
spective metals: CoO, NiO and CuO, which were
C–H
–
10 cm , and the bands of n
1
8 stretching vibrations
C–Cl
at 740 cm . The bands of skeleton vibrations occur at
–
1
–
20 and 570 cm [18–21].
1
6
In the IR spectra of 4-chloro-2-nitrobenzoates the
–1
band at 1710 cm disappears, which confirms that no
COOH is present in the complexes. In these spectra the
–
1
intense broad absorption bands at 3570–3400 cm
confirm the presence of crystallization water. The
bands arising from asymmetric and symmetric vibra-
–
1
–
tions of COO group occur at 1620–1590 and
–1
1
420–1400 cm , respectively. The bands at
1540–1530 and 1360–1350 cm are assigned to asym-
metric and symmetric vibrations of the NO group.
They are not significantly shifted with respect to those
of the parent acid, and thus one must conclude that the
NO group is not coordinated to the metal ions. The
–1
2
2
–1
nC–Cl stretching vibration occurs at 750–740 cm , and
–1
the bands at 540–490 cm are assigned to the
metal–oxygen ionic bond. The bands of skeleton vibra-
tions are shifted to lower frequencies (600 and
–1
5
50 cm ) compared to those in the acid IR spectrum.
The changes in their positions are caused by the inter-
action between aromatic ring vibrations and the groups
of atoms and ions. In the IR spectra of the complexes
the bands of nas(OCO
–
are shifted to lower frequencies
)
whereas the bands of ns(OCO
–
are moved to higher or
)
stay at the same frequencies compared to those of the
sodium salt (Table 2). Therefore it is possible to as-
sume that the carboxylate ion is a bidentate, chelating
group [18, 22, 23]. The magnitudes of separation,
, and
in the analysed complexes indicate a lower de-
gree of ionic bond in these compounds compared to so-
dium salt. Having a greater ionic potential than a so-
DnOCO
ns(OCO )
–
between the frequencies due to nas(OCO )
–
–
2+
2+
2+
dium ion, Co , Ni and Cu ions have a stronger de-
forming effect on the ligand.
In order to verify that the prepared complexes
are not converted to the nitrite isomers (during precip-
itation or on heating to 523 K), the IR spectra of the
hydrates of 4-chloro-2-nitrobenzoates, and of dehy-
drated complexes, and also of sodium nitrite were re-
corded. A survey of the literature shows that under the
influence of sunlight or with rising the temperature
the nitro complexes may be transformed to the nitrite
Table 3 Temperature range of the dehydration process of Co(II), Ni(II) and Cu(II) 4-chloro-2-nitrobenzoates in air atmosphere
and their solubility in water at 293 K
Complex
L =C H O NCl
7 3 4
Mass loss/%
–1
–3
–
DT/K
n
DH/kJ mol
Solubility/mol dm
calcd
found
11.0
11.0
4.0
–
–
–
2
4
4
CoL
NiL
Cu
2
·3H
·3H
·2H
2
O
361–395
362–393
347–364
10.5
10.5
3.7
3
3
1
108.07
125.84
60.01
1.29·10
6.62·10
4.70·10
2
2
O
2
L
4
2
O
DT – temperature range of dehydration process; n – the number of loss of water molecules; DH – enthalpy of dehydration process.
J. Therm. Anal. Cal., 86, 2006
361

FERENC et al.
identified by IR spectra, and X-ray powder diffracto-
grams. The product of the final decompositions of
chloronitrobenzoates were obtained by roasting the
analysed complexes of Co(II), Ni(II) and Cu(II).
The thermogravimetric studies of 4-chloro-2-
nitrobenzoates of Co(II), Ni(II) and Cu(II) were car-
ried out with DSC/TG technique at 293–523 K (Ta-
ble 3). The obtained results reveal the complexes to
be hydrates containing three or one molecules of wa-
ter of crystallization depending on the central ion. As
example, the TG, DTG and DTA curves of Ni(II)
Fig. 1 TG, DTG and DSC curves of Ni(II) 4-chloro-2-nitro-
benzoate
4
-chloro-2-nitrobenzoate are presented in Fig. 1. The
complexes are stable up to 300-350 K. Next in the
range of 300–400 K they dehydrate in one step. The
mass losses estimated from TG curves (3.8–10.9%)
correspond to the loss from 1 to 3 molecules of water
benzoate is the most soluble, while those of Ni(II) and
Cu(II) the least soluble salts. From the obtained re-
sults it appears that 4-chloro-2-nitrobenzoic acid may
be used as an eluent for the separation of transition
metal ions by ion-exchange chromatography.
The magnetic susceptibility of 4-chloro-2-nitro-
benzoates of Co(II), Ni(II) and Cu(II) was measured
over the range of 76–303 K (Table 4). The measured
values for Co(II) and Ni(II) complexes obey the Cu-
rie–Weiss law suggesting a weak ferromagnetic inter-
action (Fig. 2). The magnetic moment values experi-
mentally determined at 76–303 K for Co(II) and
(
the theoretical values are equal to 3.7–10.5%), and
–
1
the energetic effect (DH=60.01–125.84 kJ mol ) ac-
companying these transformation processes confirm
the losses of definitive numbers of water molecules.
The products of dehydration process were also char-
acterized by elemental analysis, IR spectra, and X-ray
powder diffractograms.
The solubilities of 4-chloro-2-nitrobenzoates of
Co(II), Ni(II) and Cu(II) in water at 293 K were mea-
sured (Table 3). They are in the order of
Ni(II) compounds change from 3.89 m
4
(at 76 K) to
B
–
4
–2
–3
.82 m (at 303 K) for Co(II) complex, and from
B
1
0 –10 mol dm . The Co(II) 4-chloro-2-nitro-
–
Table 4 Values of meff of 4-chloro-2-nitrobenzoates of Co(II), Ni(II) and Cu(II) [L =C
7 3 4
H O NCl]
CoL ·3H O NiL ·3H
2
2
2
2
O
2
Cu L
4 2
·2H O
6
6
6
T/K
M
c ·10
m
eff/m
B
T/K
M
c ·10
m
eff/m
B
T/K
M
c ·10
meff/m
B
0
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
76
23
33
43
53
63
73
83
93
03
13
23
33
43
53
63
73
83
93
03
24908
18874
17610
16599
15799
15061
14392
13927
13394
12895
12410
11980
11556
11180
10866
10558
10305
10039
9807
3.89
4.31
4.33
4.36
4.40
4.43
4.47
4.52
4.55
4.58
4.60
4.63
4.64
4.66
4.69
4.72
4.75
4.77
4.80
4.82
76
8344
6645
6268
5983
5759
5566
5316
5133
4955
4802
4634
4487
4344
4217
4110
4003
3912
3952
3744
3657
2.25
2.56
2.58
2.62
2.66
2.70
2.71
2.74
2.77
2.79
2.81
2.83
2.85
2.86
2.89
2.90
2.92
2.99
2.96
2.98
76
117
405
478
536
608
671
710
749
768
802
826
836
846
855
865
870
841
865
855
860
0.27
0.63
0.71
0.78
0.86
0.94
0.99
1.05
1.09
1.14
1.19
1.22
1.26
1.29
1.32
1.35
1.36
1.40
1.42
1.44
123
133
143
153
163
173
183
193
203
213
223
233
243
253
263
273
283
293
303
123
133
143
153
163
173
183
193
203
213
223
233
243
253
263
273
283
293
303
9568
362
J. Therm. Anal. Cal., 86, 2006

Co(II), Ni(II) AND Cu(II) 4-CHLORO-2-NITROBENZOATES
Fig. 2 Dependence between magnetic susceptibility values vs.
temperatures for Co(II) complex
Fig. 4 Relationship between magnetic moment values vs. tem-
peratures for compound of Cu(II)
spin-only magnetic moment m =1.73 m . Such de-
eff
B
pendence is a typical behaviour for copper dimer (Ta-
ble 4, Fig. 4) [34–37]. The magnetic moment values
of the Cu(II) complex decrease from 1.44 m at 303 K
B
to 0.27 m at 76 K, as a consequence of depopulation
B
of the excited triplet (S=1) state. It is well-known that
the interaction between two S=1/2 metal atoms in a
dimer leads to two molecular states: a spin singlet
(
S=0), and a triplet (S=1) separated by 2J. The inter-
action will be antiferromagnetic (J<0) if S=0 is the
ground state; on the contrary if S=1, the interaction
will be ferromagnetic (J>0) [38–42].
Fig. 3 Dependence between magnetic susceptibility values vs.
temperatures for Cu(II) 4-chloro-2-nitrobenzoate
Conclusions
2
4
.25 m (at 76 K) to 2.98 m (at 303 K) for Ni(II)
B B
-chloro-2-nitrobenzoate. These magnetic moment
4
-chloro-2-nitrobenzoates of Co(II), Ni(II) and Cu(II)
data are very close to the spin-only values for the re-
spective ions calculated from equation m =
were characterized by elemental analysis, thermal sta-
bility in air atmosphere, IR spectral data, X-ray pow-
der analysis, solubility in water at room temperature,
and magnetic properties. The obtained results indicate
them to be mono- or trihydrates. Their thermal stabil-
ity was studied at 293–523 K. It was found that on
heating in air above 523 K they decompose explo-
sively. When heated they dehydrate to form anhy-
drous salts which next are decomposed to the oxides
of the respective metals. The solubility of the ana-
lysed compounds in water (at 293 K) is of the order of
eff
1/2
[4S(S+1)] in the absence of the magnetic interaction
for present spin-system. The magnetic moment values
calculated at room temperature for Co(II), Ni(II) and
Cu(II) ions are equal to 3.88, 2.83 and 1.73 m , respec-
B
tively. For Co(II), Ni(II) and Cu(II) ions the magnetic
moment values may be different, than the spin-only
worth. In the case of Co(II) compound they are higher
than the spin-only value. This difference between mea-
sured and calculated data results from a spin-orbital
coupling [33]. For Ni(II) and Cu(II) complexes these
values are lower. This is due to fact that the vectors L
and S are aligned by the strong field of the heavy atom
in opposite directions, and this diminishes the resultant
magnetic moment. The experimental data suggest that
compounds of Co(II) and Ni(II) seem high-spin com-
plexes with probably weak ligand field [34].
–4
–2
–3
1
0 –10 mol dm . The measured values of magnetic
susceptibilities for Co(II) and Ni(II) complexes obey
the Curie–Weiss law, since they decrease with rising
temperatures. The obtained meff values of Co(II) and
Ni(II) compounds may suggest that they are high-spin
complexes with octahedral coordination, and the lig-
ands form the weak electrostatic field in the coordina-
tion sphere of central ion. The magnetic susceptibility
of 4-chloro-2-nitrobenzoate of Cu(II) increase with
rising temperatures and the magnetic moments values
suggest it to be dimer.
The magnetic susceptibility values of 4-chloro-
-nitrobenzoate of Cu(II) increase with rising temper-
2
atures suggesting a weak antiferromagnetic interac-
tion (Fig. 3). The magnetic moment values experi-
mentally determined change from 0.27 m
1
(at 76 K) to
B
9
.44 m (at 303 K). These values are lower than the d
B
J. Therm. Anal. Cal., 86, 2006
363

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