Synthesis, magnetic and spectroscopic characterization of copper(II) toluate complexes with substituted piperazines

Article abstract of DOI:10.1081/SIM-200035712

New copper(II) toluate complexes with the saturated heterocyclic bases [(L-L) having the tendency to coordinate through both 1 and 4 nitrogen atoms] 1-methylpiperazine, 1,4-dimethylpiperazine, 2,6-dimethylpiperazine and 1-phenylpiperazine have been prepared and characterized by physico-chemical and spectroscopic methods. All of the complexes were found to be antiferromagnetic with stoichiometries of the type Cu(OOCR)₂(L-L)_n (n = 1 or 0.5, R = 2-, 3-or 4-CH₃C₆H₄) except Cu(OOCC₆H₄CH₃-4)₂(L-L) (where L-L = 2,6-dimethylpiperazine), which is magnetically dilute. The spin exchange parameter, -2J, for two of the antiferromagnetic complexes has been evaluated from magnetic susceptibility measurements at different temperatures. Binuclear copper(II) acetate monohydrate-like structure for the antiferromagnetic complexes of 1:1 stoichiometry and polymeric structure of the type Cu(OOCH) ₂(dioxan)_0.5 for the complexes of 1:0.5 stoichiometry have been proposed. The magnetically dilute complex has been assigned a polynuclear trans-pseudo-octahedral or polymeric square pyramidal structure. Copyright

Full text of DOI:10.1081/SIM-200035712

Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:171–179, 2005
Copyright # 2005 Taylor & Francis, Inc.
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1081/SIM-200035712
Synthesis, Magnetic and Spectroscopic Characterization of
Copper(II) Toluate Complexes with Substituted Piperazines
B. S. Manhas and A. K. Sardana
Department of Chemistry, Punjabi University, Patiala, India
S. B. Kalia
Department of Chemistry, Himachal Pradesh University, Shimla, India
nitrogen donors generally give antiferromagnetic com-
New copper(II) toluate complexes with the saturated hetero- plexes with copper(II) acetate (Bajju, 2002; Doedens, 1976;
cyclic bases [(L-L) having the tendency to coordinate through
both 1 and 4 nitrogen atoms] 1-methylpiperazine, 1,4-dimethylpi-
perazine, 2,6-dimethylpiperazine and 1-phenylpiperazine have
been prepared and characterized by physico-chemical and spec-
troscopic methods. All of the complexes were found to be antifer-
romagnetic with stoichiometries of the type Cu(OOCR)2(L-L)n 1970). The influence of the steric and electronic characteristics
MacDougall, et al., 1976; Melnik, 1981; Melnik, 1982;
Valentine et al., 1974), whereas saturated amine donors
prefer to form magnetically dilute complexes (Kato et al.,
1964; Melnik, 1981; Oldham, 1968; Stevens and Yoke,
(n 5 1 or 0.5, R 5 2-, 3- or 4-CH3C6H4) except Cu(OOCC6H4CH3-
4)2(L-L) (where L-L 5 2,6-dimethylpiperazine), which is magneti-
cally dilute. The spin exchange parameter, 22J, for two of the
antiferromagnetic complexes has been evaluated from magnetic
susceptibility measurements at different temperatures. Binuclear
copper(II) acetate monohydrate-like structure for the antiferro- 1974), but only a few reports exist on saturated heterocyclic
of pyridine-type ligands on the structural and magnetic proper-
ties of their complexes with copper(II) acetate have been the
subject of systematic investigations (Bajju 2002; Catterick and
Thornton 1977; MacDougall et al., 1976; Valentine et al.,
magnetic complexes of 1:1 stoichiometry and polymeric structure
of the type Cu(OOCH)2(dioxan)0.5 for the complexes of 1:0.5
stoichiometry have been proposed. The magnetically dilute
complex has been assigned a polynuclear trans-pseudo-octahedral
or polymeric square pyramidal structure.
bases. In the present study, the complexation properties of
the diheterocyclic bases (L-L) (Figure 1a) 1-methylpiperazine
(1-MePipz); 1,4-dimethylpiperazine (1,4-Me2Pipz); 2,6-dimethyl-
piperazine (2,6-Me2Pipz) and 1-phenylpiperazine (1-PhPipz)
with copper(II) toluates [toluates ¼ OOCC6H4CH3-n where
n ¼ 2, 3 or 4 (Figure 1b)] have been undertaken. The interest
in the present investigations was to see the role of pKa of the
parent carboxylic acid in structure determination and the
effect of steric and electronic properties of the six-membered
saturated diheterocyclic bases on the stoichiometry, magnetic
behavior and structure of the complexes. An additional
interest to the present studies was to see whether the
heterocyclic bases, which in their free state exist in the chair
conformation, coordinate to the metal ion in their chair or in
the boat form.
Keywords Adducts, characterization, copper, magnetic, pipera-
zines, spectroscopic, synthesis, toluate
INTRODUCTION
Copper(II) acetate forms both magnetically dilute and anti-
ferromagnetic complexes with nitrogen and oxygen donor
ligands (Doedens, 1976; Kato et al., 1964; Melnik, 1981a,b;
Melnik, 1982; Oldham, 1968). The structure of the complexes
depends upon factors such as the steric characteristics of the
ligand, the stoichiometry of the complex, and reaction
EXPERIMENTAL
conditions (Bajju, 2002; Catterick and Thornton, 1977; Starting Materials
MacDougall et al., 1976; Melnik, 1981; Valentine, et al.,
1974). Oxygen donor organic ligands and pyridine-type
Liquid heterocyclic bases such as 1-MePipz, 1,4-Me2Pipz,
2,6-Me2Pipz and 1-PhPipz (all from Fluka) were dried by
refluxing and distilling over sodium hydroxide pellets before
use. The liquids obtained after distillation were stored over
sodium hydroxide beads. Acetone, n-hexane, solvent diethyl
ether and petroleum ether (40–60 8C), all from BDH, and
were purified by the usual methods.
Accepted 26 June 2004.
Address correspondence to S. B. Kalia, Department of Chemistry,
Himachal Pradesh University, Shimla 171 005, India. E-mail:
shashibalakalia@rediffmail.com
171

172
B. S. MANHAS, A. K. SARDANA AND S. B. KALIA
determined by Kjeldahl’s method in the departmental micro-
analytical laboratory. Infrared spectra of the copper(II)
toluate (ortho-, meta- and para-) complexes with heterocyclic
bases and their anhydrous sodium toluates were recorded as
KBr pellets on a Pye Unicam SP3-300 infrared spectropho-
tometer in the 4000–200 cm21 region. Electronic reflectance
spectra of the complexes (either neat or diluted with an appro-
priate amount of MgCO3) were recorded on a Unicam SP-700
UV-Visible spectrometer having a SP-735 diffuse reflectance
attachment (50,000–4,000 cm21). The X-band EPR measure-
ments (9.439–9.442 GHz) of powdered samples at room temp-
erature were made on a JES-FE3XG electron paramagnetic
resonance spectrometer. Room temperature magnetic suscepti-
bilities of all the complexes were measured on a Gouy balance
using Hg[Co(NCS)4] as a calibrant. The magnetic suscepti-
bility of the two complexes at 294, 160, 100 and 80 K were
measured on a Par-155 vibrating sample magnetometer with
a variable temperature cryostat. The measured susceptibilities
were corrected for the diamagnetic susceptibility of the
ligands. The correction for temperature was taken as
60 ꢀ 1026 c.g.s. units per gram atom of copper(II) ions.
RESULTS AND DISCUSSION
FIG. 1. Structures of the ligands, (a) heterocyclic bases (L-L) and (b) sodium
Adducts of copper(II) toluates with substituted piperazines
were obtained by reacting copper(II) toluates and piperazine
in 1:0.5, 1:1 and 50% excess of stoichiometric amounts
whereby the bases yield complexes only with the 1:1 and
1:0.5 stoichiometries (Eq. 3 and 4). Copper(II) toluates were
prepared by reacting copper(II) sulfate with stoichiometric
amounts of sodium salts of the corresponding toluic acids in
a water-acetone mixture.
toluates.
Preparation of Copper(II) Toluates (ortho-, meta- and para)
The copper(II) toluates were synthesised by the method
described earlier (Manhas et al., 2003).
Preparation of Complexes
Copper(II) toluate (1 g, 2.99 mmol), prepared by the method
described earlier (Manhas et al., 2003), was suspended in
diethyl ether (30 mL) in a round-bottomed flask. A solution
of the stoichiometric amount (1.50 mmol or 2.99 mmol) of
the heterocyclic base in the same solvent (15 mL) was added
drop-wise after successive intervals of 10 min over a total
period of about 2.5 h to the continuously stirred suspension
of copper(II) toluate. Colored solutions, as indicated in
Table 1, of the adducts were obtained as the solid copper(II)
toluate dissolved. Solid adducts of the bases separated after
the contents had been stirred for another two hours and then
cooled. The separated product was filtered in a G4 filtration
unit, washed with acetone and diethyl ether, dried under
vacuum and placed in a desiccator containing anhydrous
calcium chloride.
HOOCC6H4CH3-n þ NaOH
ꢁ! NaOOCC6H4CH3-n þ H2O
½1ꢂ
2ðNaOOCC6H4CH3-nÞ þ CuSO4 ꢃ 5H2O
ꢁ! CuðOOCC6H4CH3-nÞ2 þ Na2SO4 þ 5H2O ½2ꢂ
CuðOOCC6H4CH3-nÞ2 þ ðL-LÞ
ꢁ! CuðOOCC6H4CH3-nÞ2ðL-LÞ
½3ꢂ
½4ꢂ
CuðOOCC6H4CH3-nÞ2 þ 0:5ðL-LÞ
ꢁ! CuðOOCC6H4CH3-nÞ2ðL-LÞ0:5
where n ¼ 2, 3 or 4 and (L-L) ¼ 1-MePipz; 1,4-Me2Pipz;
Elemental Analyses and Physical Measurements
The metal content in the complexes was determined
2,6-Me2Pipz and 1-PhPipz.
The complexes are insoluble in organic solvents and do not
volumetrically by EDTA titration using xylenol orange as indi- melt, but decompose above 185 8C. Chemical formulae based
cator. Carbon and hydrogen analyses were performed on upon elemental analyses, colors and particulars of method of
an automatic Coleman-33 analyzer, while nitrogen was preparation of complexes are listed in Table 1.

CHARACTERIZATION OF COPPER(II) TOLUATE COMPLEXES
173
TABLE 1
Elemental analysis (%). found (calcd.), colours and particulars of the method of preparation of the complexes
Elemental analysis, found (calcd.) (%)
Compound (empirical formula)
(formula weight)
Yield
(%)
S.a. or
excessa
Dec. p.
( 8C)
Cu
C
H
N
Color
Cu(OOCC6H4CH3-4)2(1-MePipz)
(C21H26CuN2O4) (433.5)
90
95
90
85
75
80
80
85
90
95
80
85
65
70
80
85
80
80
70
80
14.76
(14.64)
16.68
57.72
(58.12)
57.33
5.84
(6.04)
4.98
6.85
(6.45)
3.61
Pale
blue
Pale
blue
Pale
green
Pale
green
Violet
Excess
S.a.
230
225
200
210
190
200
190
200
220
230
210
215
200
195
205
200
220
190
190
190
Cu(OOCC6H4CH3-4)2(1-MePipz)0.5
(C18.5H20CuNO4) (383.5)
(16.55)
14.53
(57.88)
58.48
(5.25)
5.95
(3.65)
6.21
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)
(C22H28CuN2O4) (447.5)
Excess
S.a.
(14.18)
16.65
(58.98)
58.88
(6.30)
4.91
(6.25)
3.66
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)0.5
(C19H21CuNO4) (390.5)
(16.26)
14.17
(58.38)
58.53
(5.41)
5.80
(3.58)
6.68
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)
(C22H28CuN2O4) (447.5)
Excess
S.a.
(14.18)
16.24
(58.98)
58.84
(6.30)
5.68
(6.25)
4.01
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)0.5
(C19H21CuNO4) (390.5)
Dirty
grey
Pale
green
Sky
blue
Pale
blue
(16.26)
12.71
(58.38)
62.79
(5.41)
5.31
(3.58)
5.25
Cu(OOCC6H4CH3-4)2(1-PhPipz)
(C26H28CuN2O4) (495.5)
S.a.
(12.81)
15.18
(62.95)
60.61
(5.69)
5.56
(5.65)
3.49
Cu(OOCC6H4CH3-4)2(1-PhPipz)0.5
(C21H21CuNO4) (414.5)
S.a.
(15.31)
14.71
(60.79)
58.02
(5.10)
5.87
(3.38)
6.19
Cu(OOCC6H4CH3-3)2(1-MePipz)
(C21H26CuN2O4) (433.5)
Excess
S.a.
(14.64)
16.18
(58.12)
57.62
(6.04)
4.76
(6.45)
3.66
Cu(OOCC6H4CH3-3)2(1-MePipz)0.5
(C18.5H20CuNO4) (383.5)
Green
(16.55)
14.61
(57.88)
58.58
(5.25)
5.93
(3.65)
5.98
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)
(C22H28CuN2O4) (447.5)
Pale
S.a.
(14.18)
16.06
(58.98)
58.88
(6.30)
4.89
(6.25)
3.92
green
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)0.5
(C19H21CuNO4) (390.5)
Yellowish
green
Blue
S.a.
(16.26)
13.93
(58.38)
58.99
(5.41)
6.22
(3.58)
6.35
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)
(C22H28CuN2O4) (447.5)
Excess
S.a.
(14.18)
15.91
(58.98)
58.18
(6.30)
5.91
(6.25)
3.24
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)0.5
(C19H21CuNO4) (390.5)
Pale
green
Pale
(16.26)
12.71
(58.38)
62.74
(5.41)
5.82
(3.58)
5.93
Cu(OOCC6H4CH3-3)2(1-PhPipz)
(C26H28CuN2O4) (495.5)
S.a.
(12.81)
15.39
(62.95)
60.29
(5.69)
5.55
(5.65)
3.12
green
Green
Cu(OOCC6H4CH3-3)2(1-PhPipz)0.5
(C21H21CuNO4) (414.5)
S.a.
(15.31)
16.34
(60.79)
58.04
(5.10)
5.89
(3.38)
3.83
Cu(OOCC6H4CH3-2)2(1,4-Me2Pipz)0.5
(C19H21CuNO4) (390.5)
Pale
green
Pale
Excess
S.a.
(16.26)
14.12
(58.38)
58.64
(5.41)
6.77
(3.58)
6.05
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)
(C22H28CuN2O4) (447.5)
(14.18)
16.52
(58.98)
58.47
(6.30)
5.91
(6.25)
3.59
green
Green
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)0.5
(C19H21CuNO4) (390.5)
S.a.
(16.26)
15.18
(15.31)
(58.38)
61.28
(60.79)
(5.41)
5.46
(5.10)
(3.58)
2.99
(3.38)
Cu(OOCC6H4CH3-2)2(1-PhPipz)0.5
(C21H21CuNO4) (414.5)
Blue
S.a.
aIndicates as to whether the heterocyclic base was taken in stoichiometric amount (S.a.) or in excess.
IR Spectra
Since both the acetate group and the heterocyclic base can
and Thornton, 1977) is based upon the difference in the
na(OCO) and ns(OCO) values, and (2) the directions of shifts
criterion (Manhas and Trikha, 1982), which depends upon
the directions of the na(OCO) and ns(OCO) shifts in the com-
plexes compared to their values in sodium acetate. Of these,
the latter criterion is considered to be more important. Examin-
ation of the positions and directions of the shifts of na(OCO)
coordinate to the metal ion in a bidentate or monodentate
fashion, in principle, many structural arrangements are
possible. In the absence of definitive structural data, two
criteria are currently employed to determine the coordinating
mode of acetate groups, viz.; (1) the ‘D criterion’ (Catterick

174
B. S. MANHAS, A. K. SARDANA AND S. B. KALIA
and ns(OCO) of the carboxylate group in the complexes as the nitrogen atom of the .N–CH3 group no longer has a
compared to their positions in sodium toluates (Table 2) lone pair of electrons and it acquired a partial positive charge
suggests a bridging bidentate mode of coordination of the due to its coordination with the metal ion (Manhas and
carboxylate group for all of the complexes.
Trikha, 1978; Braunholtz et al., 1958; Manhas et al., 1979).
The band due to n(N-H) in the complexes of the bases However, in some complexes (Table 2) the absence of any
1-MePipz, 2,6-Me2Pipz and 1-PhPipz, appears at lower wave noticeable shift of the bands due to n(C–H) of .N–CH3
numbers relative to its position in the free bases, thus clearly excludes the possibility of coordination of the nitrogen atom
indicating the coordination of the bases through the nitrogen of the N–CH3 group (Manhas and Trikha, 1978; Braunholtz
atom of the N–H groups. The band due to the C–H stretching et al., 1958; Manhas et al., 1979). No new bands of low or
frequency of the N–CH3 group in the complexes of the medium intensity (characteristic of the boat configuration)
bases 1-MePipz and 1,4-Me2Pipz either disappears or shifts appear in the region 1,500–700 cm21, thus indicating that
to the higher energy region. In the case of disappearance, the bases are coordinated in the same form as in the free
these bands probably shift to the higher energy region state, i.e., in the chair form. The appearance of additional
(2,900 cm21) and overlap with stretching vibrational bands of bands around 450 cm21 and 310 cm21 as compared to the
other C–H bonds of the complexes. This shift indicates that infrared spectra of uncomplexed cupric carboxylate and the
TABLE 2
Some coordinatively diagnostic features of infrared spectra (cm21) of sodium salts of carboxylic acids, heterocyclic bases and
their copper(II) complexes
n(C–H)
N–CH3 or
N–C6H5
Compound
n(N-H)
na(OCO)
nb(OCO)
n(Cu–O)
n(Cu–N)
4-CH3C6H4COO Na
3-CH3C6H4COO Na
2-CH3C6H4COO Na
1-MePipz
—
—
—
—
1,545 s
1,560 s
1,515 s
1,406 vs
1,405 vs
1,403 vs
—
—
—
—
—
—
—
3,280 m
—
2,680 m
2,820 m
2,680 m
2,840 m
1,4-Me2Pipz
—
—
2,6-Me2Pipz
1-Phpipz
3,265 m
3,300 m
3,200 m
3,190 m
—
—
a
Cu(OOCC6H4CH3-4)2(1-MePipz)
Cu(OOCC6H4CH3-4)2(1-MePipz)0.5
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-4)2(1-PhPipz)
Cu(OOCC6H4CH3-4)2(1-PhPipz)0.5
Cu(OOCC6H4CH3-3)2(1-MePipz)
Cu(OOCC6H4CH3-3)2(1-MePipz)0.5
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-3)2(1-PhPipz)
Cu(OOCC6H4CH3-3)2(1-PhPipz)0.5
Cu(OOCC6H4CH3-2)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-2)2(1-PhPipz)0.5
2,780 m
a
1,555 s
1,552 s
1,585 s
1,560 s
1,552 s
1,595 s
1,560 s
1,555 s
1,575 s
1,575 s
1,572 s
1,580 s
1,560 s
1,570 s
1,570 s
1,572 s
1,570 s
1,565 s
1,565 s
1,565 s
1,406 vs
1,405 vs
1,406 vs
1,408 vs
1,406 vs
1,408 vs
1,408 vs
1,418 vs
1,420 vs
1,410 vs
1,410 vs
1,405 vs
1,405 vs
1,415 vs
1,390 vs
1,420 vs
1,402 vs
1,430 vs
1,405 vs
1,420 vs
452 m
450 m
446 m
455 m
415 m
422 m
450 m
435 m
435 m
405 m
445 m
445 m
430 m
480 m
475 m
420 m
450 m
460 m
475 m
405 m
290 s
300 s
295 s
305 s
280 s
295 s
305 s
305 s
300 s
285 s
290 s
280 s
278 s
275 s
320 s
330 s
285 s
310 s
305 s
295 s
a
a
—
3,060 m
3,070 m
3,295 m
3,280 m
3,125 m
3,280 s
—
—
—
2,850 m
a
2,780 m
a
a
a
—
3,130 m
3,260 m
3,280 m
3,210 m
—
—
—
2,840 m
a
a
3,245 m
3,230 m
3,270 m
—
—
a
ameans absorbance is not observed clearly.

CHARACTERIZATION OF COPPER(II) TOLUATE COMPLEXES
175
free bases have tentatively been assigned to n(Cu–O) and (2pp (donor oxygen atom) ! (dx22y2)ꢄ) charge transfer tran-
n(Cu–N) modes of vibrations, respectively (Manhas and sition (Dubicki, 1972; Dubicki and Martin, 1966). All other
Trikha, 1978; Marcotrigiano et al., 1972; Battaglia, 1980; complexes show a broad band in the region 12,500-
Manhas and Dhindsa, 1989).
14,925 cm21 in their diffuse electronic reflectance spectra
(Table 3). It is a composite band (band I) and is considered
to contain bands due to the dxz, dyz ! dx22y2 and
dxy ! dx22y2 electronic transitions for copper(II) ion in tetra-
gonal environments. The band II, which appears as a
shoulder at about 32,000 2 37,000 cm21, is assigned to the
charge transfer transition 2pp(O) ! (dx22y2)ꢄ (Dubicki, 1972;
Dubicki and Martin, 1966).
Electronic Reflectance Spectral Studies
The complex Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz) shows
two bands around 16,000 and 20,000cm21 in its diffuse
electronic reflectance spectrum. The appearance of these bands
indicates tetragonal distortion (D4h symmetry) of the octa-
hedral field for the copper(II) ion in this complex. The lower
2
and higher energy bands can be assigned to B2g
2
2B1g(dxy ! dx22y2) and Eg 2B1g (dxz, dyz ! dx22y2) ligand
EPR Studies
The X-band EPR curve of powdered material for the magne-
field transitions (Hathaway and Billing, 1970). Here the
difference between the two ‘d-d’ transitions is apparently tically dilute copper(II) complex Cu(OOCC6H4CH3-4)2(2,6-
larger. The splitting into two of the electronic spectral band Me2Pipz) has been obtained at room temperature and is con-
2
(due to the T2g
2Eg transition), expected for a regular sistent with the axial symmetry of the complex. The magnitude
octahedral copper(II) complex, is not surprising. Most of g (2.2866) and g (2.0916) obtained from the EPR
k
?
copper(II) complexes are distorted due to the Jahn-Teller spectrum for this complex is consistent (g . g . 2.04)
k
?
effect. Moreover, in the present case the complexes are with an elongated type structure, and hence dx22y2 as the
bound to be distorted due to the large difference in the ligand higher energy orbital. This agrees with the results obtained
field strengths of carboxylate ligands and the bases. Another from electronic absorption studies (Attanasio et al., 1974;
band at 33,335 cm21 is probably due to the ligand ! metal Hathaway and Billing, 1970). The observed range of g is in
k
TABLE 3
Electronic reflectance spectral data (cm21) and room temperature meff values of the magnetically dilute and
antiferromagnetic copper(II) toluates with substituted piperazines
Absorption II
(ligand ! metal charge
Absorption I
d-d transitions
Compound
transfer transitions)
m
eff (B.M.)
1.870
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)
16,000
20,000
13,700
13,795
13,160
12,500
14,925
13,605
14,285
13,985
13,795
12,985
13,515
13,700
13,795
13,700
13,515
13,160
13,335
13,890
14,085
33,335
Cu(OOCC6H4CH3-4)2(1-MePipz)
Cu(OOCC6H4CH3-4)2(1-MePipz)0.5
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-4)2(1-PhPipz)
1.372
1.420
1.404
1.420
1.460
1.368
1.347
1.398
1.451
1.295
1.360
1.546
1.411
1.470
1.482
1.472
1.414
1.420
1.339
36,365
34,485
33,335
35,715
33,335
33,900
35,090
35,715
35,715
37,035
30,770
35,715
37,035
35,715
37,035
37,035
35,715
35,090
Cu(OOCC6H4CH3-4)2(1-PhPipz)0.5
Cu(OOCC6H4CH3-3)2(1-MePipz)
Cu(OOCC6H4CH3-3)2(1-MePipz)0.5
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-3)2(1-PhPipz)
Cu(OOCC6H4CH3-3)2(1-PhPipz)0.5
Cu(OOCC6H4CH3-2)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-2)2(1-PhPipz)0.5

176
B. S. MANHAS, A. K. SARDANA AND S. B. KALIA
conformity with the CuO4N2 chromophore of the complex Magnetic Susceptibility Studies
(Attanasio et al., 1974). The orbital reduction factors
K2 ¼ 0.6855 and K2 ¼ 1.0764 (K2 , K2 suggests that in-
The room temperature magnetic moment for the
complex Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz) is 1.87 B.M.,
i.e., greater than the spin-only value for one unpaired
electron (d9 system), indicating the complex to be magneti-
cally dilute while all the other complexes have meff values
in the 1.34–1.54 range (Table 3), which is similar to the
values reported earlier for antiferromagnetic dinuclear or
polynuclear complexes where carboxylate groups bridge
between two metal ions (Table 5) (Catterick and Thornton
1977; Doedens 1976; Melnik 1981a, b; Melnik 1982).
k
?
k
?
plane p-bonding may be dominating. These values are compar-
able to other copper(II) systems (actually K2 ¼ l l0 and
k
k/
K2 ¼ l l0 where l0 is spin-orbit coupling constant for free
?
copper(II) ion and l and l are effectively reduced spin-
k/
k
?
orbit coupling constants due to covalency in the complexes
Hathaway and Billing, 1970). The calculated value of
G ¼ 3.1825, which is ,4.0, shows that significant exchange
coupling is present and the misalignment is appreciable.
The X-band EPR spectra at 300 K for powdered samples of
antiferromagnetic complexes in the present discussion contain
The Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz) and Cu(OOCC6-
H4CH3-2)2(2,6-Me2Pipz) complexes have been characterized
by magnetic susceptibility measurements at 294, 160, 100
and 80 K. The magnetic moments for the two complexes
decrease with a decrease of temperature, while the magnetic
susceptibility of the first complex increases and that of the
second complex decreases with a decrease of temperature.
The increase of the magnetic susceptibility with decreasing
temperature for Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz) suggests
that the complex either has a spin-exchange parameter (–2J)
considerably smaller than the other complex or it has a much
higher proportion of the magnetically dilute impurity, which
is commonly found in antiferromagnetic complexes. Hence,
the following modified equation, based upon Bleaney and
Bower’s model (Bleaney and Bowers, 1952) which takes into
consideration the presence of a paramagnetic impurity, was
employed to evaluate the value of –2J from magnetic
absorption lines at field strengths of 600 (Hz1), 4700 (H ), and
?
6100G (Hz2), which are characteristic features of axially sym-
metric binuclear copper(II) species and correspond to the spin
triplet state (S ¼ 1) with D . hn and E ¼ 0 (Smith and
Pilbrow, 1974) (Table 4). The range of g or gz (2.34–2.51),
k
g
(2.10–2.16) and D (0.34–0.40 cm21) evaluated from the
?
EPR spectra are comparable with the earlier reported values
for binuclear copper(II) carboxylate complexes (Catterick
and Thornton, 1977; Jotham et al., 1972; Melnik, 1981;
Melnik, 1982). However, in addition to the above mentioned
absorptions, an absorption line around 3200 G is also
observed. This line has been attributed to the magnetically
dilute copper(II) impurity which is commonly present in
copper(II) arylcarboxylate complexes (Newton et al., 1980;
Thompson et al., 1971; Wasson et al., 1968).
TABLE 4
Electron paramagnetic resonance spectral parameters of antiferromagnetic complexes
Compound
g
g
gav
jDj(cm21
)
?
k
Cu(OOCC6H4CH3-4)2(1-MePipz)
Cu(OOCC6H4CH3-4)2(1-MePipz)0.5
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)
Cu(OOCC6H4CH3-4)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-4)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-4)2(1-PhPipz)
2.0976
2.1357
2.1087
2.1216
2.1382
2.0957
2.1607
2.0976
2.1014
2.1249
2.1391
2.1024
2.1018
2.1188
2.1119
2.1311
2.1266
2.1244
2.1135
2.4529
2.5099
2.4529
2.4983
2.4529
2.4485
2.3463
2.4529
2.4416
2.4418
2.4983
2.4641
2.4527
2.4202
2.4757
2.4757
2.4754
2.4866
2.4485
2.2160
2.2604
2.2234
2.2472
2.2431
2.2133
2.2226
2.2160
2.2148
2.2305
2.2588
2.2230
2.2188
2.2193
2.2332
2.2460
2.2429
2.2451
2.2252
0.3722
0.3706
0.3722
0.3733
0.3722
0.3710
0.3423
0.3722
0.3741
0.3976
0.3966
0.3754
0.3751
0.3743
0.3786
0.4017
0.3988
0.4049
0.371
Cu(OOCC6H4CH3-4)2(1-PhPipz)0.5
Cu(OOCC6H4CH3-3)2(1-MePipz)
Cu(OOCC6H4CH3-3)2(1-MePipz)0.5
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)
Cu(OOCC6H4CH3-3)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-3)2(1-PhPipz)
Cu(OOCC6H4CH3-3)2(1-PhPipz)0.5
Cu(OOCC6H4CH3-2)2(1,4-Me2Pipz)0.5
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)0.5
Cu(OOCC6H4CH3-2)2(1-PhPipz)0.5

CHARACTERIZATION OF COPPER(II) TOLUATE COMPLEXES
177
TABLE 5
Magnetic susceptibility (x1Cu ꢀ 106) (c.g.s units) data and values of spin exchange parameter (22J) (cm21) of antiferromagnetic
complexes and pKa of axial ligand and carboxylic acid
Diamagnetic x1Cu ꢀ 106 ¼ [(xcorr Cu 2 Na) ꢀ 106]
correction
Carboxylic Axial ligand
pKa
Compound
(ꢀ106)
294 K
1,017
160 K
1,078
100 K
1,108
80 K
acid pKa
22J
Cu(OOCC6H4CH3-3)2(2,6-Me2Pipz)
254
1,108
4.252
pKa1 ¼ 9.570 274
pKa2 ¼ 5.400
Cu(OOCC6H4CH3-2)2(2,6-Me2Pipz)
254
848
652
522
456
3.870
pKa1 ¼ 9.570 315
pKa2 ¼ 5.400
susceptibility data at different temperatures (Thompson et al., shown in Figure 2a or 2b where the carboxylate ligand
1971; Newton et al., 1980).
behaves as a bridging bidentate group. The structure in
Figure 2a is polynuclear trans-pseudo-octahedral. Here the car-
boxylate group and the base L-L both act as bridging bidentate
ligands, while Figure 2b shows that the carboxylate group acts
as a bidentate ligand and the base L-L acts as a unidentate
ligand (while taking the axial position) to give a polynuclear
square pyramidal structure to the complex. Although in these
ꢀ
ꢁ
Ngꢁ2b2ð1 ꢁ xÞ
2J
ln
ꢁ 3 ¼ ꢁ
kTðxCu ꢁ 0:43x=T ꢁ NaÞ
kT
2J
or ln ðF ꢁ 3Þ ¼ ꢁ
kT
½5ꢂ
The unknown quantities in this expression on the left hand
side were assumed as follows: the value of (g¯ ¼ 2.17 normally
found for copper(II) alkanoates and the value of Na assumed
to be constant at 60 ꢀ 1026 c.g.s units (Jotham et al., 1972).
The value of x, the mole fraction of paramagnetic impurity,
was chosen to give the best fit with the above equation.
Values of –2J equal to 274 and 315 cm21 for the Cu(OOCC6-
H4CH3-3)2(2,6-Me2Pipz) and Cu(OOCC6H4CH3-2)2(2,6-
Me2Pipz) complexes, respectively, were obtained from the
slopes (2J/K) of the plots of ln (F-3) versus 1/T. The
former complex was found to have
a spin-exchange
parameter (22J), which is considerably smaller than that of
the other complex. The range of values for –2J of the
present complexes with axial ligands having high donor
ability (saturated amines) and is comparable to other
aromatic nitrogen donor axial ligands (pyridine or quinoline,
etc.) with less donor ability. The electronic nature of the
axial ligand in the two complexes being kept the same, the
large difference in the values of –2J and their order of mag-
nitude show a direct relationship with the pKa values and,
hence, the donor strengths of the parent ortho- and meta-
toluic acids. Ortho-toluate with a lower pKa value of its
acid and higher acid strength (ortho effect) as compared to
that of meta-toluate (Table 3) acts as a better donor. This
results in the greater energy separation between the lower
lying singlet and higher lying triplet energy states and,
hence, a higher value of –2J in its copper(II) complex. This
is in conformity with the earlier existing results of Jotham
et al. (Jotham et al., 1972) where it has been stated that –2J
increases as either the terminal ligands or the bridging
ligands become better donors.
On the basis of the spectroscopic data, the complex
FIG. 2. Proposed structures of the complex Cu(OOCC6H4CH3-4)2(2,6-Me2-
Cu(OOCC6H4CH3-4)2 (2,6-Me2Pipz) may have the structure Pipz) (R ¼ 4-CH3C6H4).

178
B. S. MANHAS, A. K. SARDANA AND S. B. KALIA
structures there are two bridging carboxylate groups, there is
Overall, if we compare the room temperature meff values for
very little interaction of the unpaired electrons on the two inter- the whole series of complexes we are unable to make any
acting copper ions via the intermediate carboxylate groups. convincing relationship with electronic and steric effects of
This is in contrast to the copper(II) acetate monohydrate struc- the carboxylate as well as that of the heterocyclic secondary
ture in which dxy orbitals of copper ion interact with p orbitals amine ligands. However, the steric hindrance of the amine
of oxygens and the superexchange mechanism is made possible ligands plays an important role in determining the stoichi-
since the significant mixing of the magnetically important ometry, structure, and, hence, the magnetic properties (mag-
sigma-bonding (dx22y2) wave functions into p-bonding (dxy) netically dilute and antiferromagnetic character) of the
orbitals enables the delocalized p orbital system of bridging complexes. Though the pKa of 4-toluic acid (4.360) is
groups to become available. However, in the above-mentioned comparatively larger than that of 2-toluic acid (3.870) and
case, this type of mixing has to be very small as the energy 3-toluic acid (4.257), the smaller steric hindrance of the
difference between dxz, dyz and dx22y2 orbitals is much methyl group at the 4-position on the aryl ring in comparison
greater than that between dxz and dx22y2. This conclusion is cor- to that of 2- and 3-toluic acids, appears to favor the formation
of a magnetically dilute complex only with the base 2,6-
Me2Pipz, while all other bases yield antiferromagnetic
complexes.
roborated by the fact that in some Cu–O–Cu and
and bridged complexes where dxy and dxz, dyz orbitals of the
copper atoms are the p-interacting orbital(s) in the bridge,
the magnetic exchange does not occur (Carlisle and Hatfield,
1970; Gruber et al., 1968; Hall and Waters, 1960;
Hatfield, 1970; Hatfield, 1972; Lewis and Walton, 1966;
Villa et al., 1970; Villa and Hatfield, 1970; Villa and
Hatfield, 1971). For the antiferromagnetic complexes, a
copper(II) acetate monohydrate-like binuclear structure
(De Meester et al., 1973) may be assigned to the complexes
of the type Cu(OOCR)2(L-L). A polymeric structure similar
to Cu(OOCH)2(dioxan)0.5 (Figure 3) with carboxylate groups
acting as bridging bidentate between two copper ions and the
heterocyclic base (L-L) joining the two bridging units
through copper atoms may be assigned to all the other
antiferromagnetic complexes of the type Cu(OOC6H4CH3-n)2
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