Synthesis, magnetic, and spectral studies of some mixed-ligand complexes of copper(II) involving diphenic acid and pyridine or aniline derivatives

Article abstract of DOI:10.1081/SIM-120020331

New mixed-ligand hexa-coordinated diphenato complexes of copper(II) having the general formula [Cu(DPA)(L)₂], where DPAH₂ = diphenic acid and L = nicotinamide (NICA), 2-cyanopyridine (2-CPY), 3-cyanopyridine (3-CPY) and 4-cyanopyridine (4-CPY) or aniline derivatives, such as, o-toluidine (o-TD), m-toluidine (m-TD) or o-phenetidine (o-PD), have been prepared by the interaction of an aqueous solution of cupric chloride and ethanolic solutions of diphenic acid and the corresponding ligand L, in the mole ratio of 1:1:2. The resulting products have been characterized on the basis of analytical data, molar conductances, magnetic measurements, infrared, electronic and electron spin resonance spectral studies. All of the complexes are thermally stable and behave as non-electrolytes. A square-planar geometry has been suggested for these complexes.

Full text of DOI:10.1081/SIM-120020331

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Synthesis, Magnetic, and Spectral Studies of Some
Mixed‐Ligand Complexes of Copper(II) Involving
Diphenic Acid and Pyridine or Aniline Derivatives
R. C. Maurya a , P. Sharma a & D. Sutradhar a
a Coordination Chemistry Laboratory, Department of P.G. Studies and Research in Chemistry,
R.D. University, Jabalpur, 482‐001, India
Version of record first published: 15 Feb 2007.
To cite this article: R. C. Maurya , P. Sharma & D. Sutradhar (2003): Synthesis, Magnetic, and Spectral Studies of Some
Mixed‐Ligand Complexes of Copper(II) Involving Diphenic Acid and Pyridine or Aniline Derivatives, Synthesis and Reactivity in
Inorganic and Metal-Organic Chemistry, 33:4, 669-682
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 4, pp. 669–682, 2003
Synthesis, Magnetic, and Spectral Studies of
Some Mixed-Ligand Complexes of Copper(II)
Involving Diphenic Acid and Pyridine or
Aniline Derivatives
*
R. C. Maurya, P. Sharma, and D. Sutradhar
Coordination Chemistry Laboratory, Department of P. G. Studies and
Research in Chemistry, R. D. University, Jabalpur, India
ABSTRACT
New mixed-ligand hexa-coordinated diphenato complexes of copper(II)
having the general formula [Cu(DPA)(L)2], where DPAH2 = diphenic
acid and L = nicotinamide (NICA), 2-cyanopyridine (2-CPY), 3-
cyanopyridine (3-CPY) and 4-cyanopyridine (4-CPY) or aniline deri-
vatives, such as, o-toluidine (o-TD), m-toluidine (m-TD) or o-phene-
tidine (o-PD), have been prepared by the interaction of an aqueous
solution of cupric chloride and ethanolic solutions of diphenic acid and
the corresponding ligand L, in the mole ratio of 1:1:2. The resulting
products have been characterized on the basis of analytical data, molar
*
Correspondence: R. C. Maurya, Coordination Chemistry Laboratory, Department of
P. G. Studies and Research in Chemistry, R. D. University, Jabalpur 482-001, India;
E-mail: rcmaurya@sancharnet.in.
669
DOI: 10.1081/SIM-120020331
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

670
Maurya, Sharma, and Sutradhar
conductances, magnetic measurements, infrared, electronic and electron
spin resonance spectral studies. All of the complexes are thermally stable
and behave as non-electrolytes. A square-planar geometry has been sug-
gested for these complexes.
Key Words: Diphenic acid; Mixed-ligand complexes; (4 + 2) Cu(II)
compounds.
INTRODUCTION
Diphenic acid has been used as an analytical reagent[1] and as a bidentate
ligand in the formation of complexes with transition metal ions.[2] Studies on
some mixed-ligand complexes of cobalt(II), nickel(II), copper(II), palladiu-
m(II), platinum(II), manganese(II), zinc(II), iron(II) and iron(III) with
diphenic acid as primary and some heterocyclic bases as secondary ligand
are available in the literature.[1,3–6] However, there is no report on mixed-
ligand complexes of copper(II) involving diphenic acid and pyridine or aniline
derivatives. It was, therefore, thought worthwhile to synthesize and
characterize some mixed-ligand copper(II) diphenates with pyridine deriva-
tives, viz., nicotinamide (NICA), 2-cyanopyridine (2-CPY), 3-cyanopyridine
(3-CPY) and 4-cyanopyridine (4-CPY) or aniline derivatives, such as, o-
toluidine (o-TD). m-toluidine (m-TD) and o-phenetidine (o-PD). The present
paper describes the results at such a study. The structures of diphenic acid and
the other ligands used in the present investigation are shown in Figure 1.
EXPERIMENTAL
Materials
Nicotinamide (Sisco Chem. Industries, Bombay), 2-, 3- and 4-
cyanopyridines (Nepera, New-York), o-toluidine, m-toluidine and cupric
chloride dihydrate (B.D.H. Chemicals, Bombay), o-phenetidine (Aldrich
Chemical Company, U.S.A.) and diphenic acid (E. Merck, India), were
used as supplied.
Synthesis at Mixed-Ligand Complexes
An aqueous solution (10 mL) of cupric chloride dihydrate (1.70 g, 10
mmol) was added to the ethanolic solutions (20 mL) of diphenic acid

Mixed-Ligand Complexes of Copper(II)
671
Figure 1. Structures of ligands.
(2.42 g, 10 mmol) and the corresponding pyridine/aniline derivative (20
mmol) in the mole ratio 1:1:2. The resulting mixture was then refluxed at
80 °C over a hot plate with magnetic stirrer, for the duration given below
in each case:
Ligand
Duration, h
NICA
2-CPY
3-CPY
4-CPY
o-TD
1.45
1.5
1.5
1.5
2.0
2.0
2.5
m-TD
o-PD

672
Maurya, Sharma, and Sutradhar
During this time a coloured mass separated out. It was filtered by
suction, washed 4 to 5 times with ethanol and dried in a desiccator over
anhydrous CaCl2 at room temperature.
Analyses
Carbon, hydrogen and nitrogen were determined microanalytically on a
Carlo Erba 1108 elemental analyzer at the Central Drug Research Institute,
Lucknow, India. The copper content in the complexes was determined by
the standard method.[7]
Physical Methods
The IR spectra were recorded (4000–400 cm ꢀ 1) as Nujol mulls on a
Perkin-Elmer model 1620 FT-IR spectrophotometer, Electronic spectra
were recorded in 10 ꢀ 3 M DMF solutions on a Shimadzu model UV–160
spectrophotometer; EPR spectra were recorded at 298 K on a Bruker
spectrometer at the microwave frequency 9.45 GHz and magnetic field
around 3000 G. Room temperature molar conductances in 10–3 M DMF
solutions were measured on a Toshniwal conductivity bridge fitted with a
dip-type cell (cell constant 1.3 cm ꢀ 1). Decomposition temperatures of the
complexes were determined using an electrothermal apparatus having the
capacity to record temperatures up to 360 °C. Room temperature magnetic
measurements were performed by Gouy’s method using mercury(II) tetra-
thiocyanatocobaltate(II) as the calibrant.
RESULTS AND DISCUSSION
The mixed-ligand complexes of copper(II) were prepared according to
the following equation:
Ethanol
CuCl2ꢁ2H2O þ DPAH2 þ 2L ꢀꢀꢀꢀꢀꢀ! ½CuðDPAÞðLÞ2ꢂ þ 2HCl þ 2H2O
Refluxð80 °CÞ
Where L = NICA (1), 2-CPY (2), 3-CPY (3), 4-CPY (4), o-TD (5), m-TD
(6) and o-PD (7) and DPAH2 = diphenic acid.
All of the compounds are air-stable, non-hygroscopic, coloured so-
lids (see Table 1 for colors). The analytical data and some physical pro-
perties of the complexes are also given in Table 1. The solubilities of these

Mixed-Ligand Complexes of Copper(II)
673

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Maurya, Sharma, and Sutradhar

Mixed-Ligand Complexes of Copper(II)
675

676
Maurya, Sharma, and Sutradhar
complexes in different solvents are recorded in Table 2. The resulting
compounds were characterized on the basis of the following studies.
Conductance Measurements
The observed molar conductances of these mixed-ligand complexes are
given in Table 3, and are consistent with the non-electrolytic[8] nature of
the complexes.
Magnetic Measurements
Copper(II) has a d[9] electronic configuration and its complexes
contain one unpaired electron in the 3d shell. The majority of the com-
plexes are formed by involvement of d-orbitals and they are square-planar
or distorted-octahedral. Jahn Tellar distortions play a major role in the
distortions of the geometry of the complexes. The formation of tetrahedral
complexes of copper(II), with no involvement of d-orbitals has also been
reported.[9] In cases where the copper(II) complexes display magnetic
moments values equivalent to one unpaired electron, the complexes are
referred to as magnetically dilute. In such complexes the paramagnetic
metal centres are situated apart and the metal ions are surrounded by
ligand molecules in such a way that the unpaired spins of neighbouring
metal ions remains unaffected. In the case of tetrahedral or distorted-
octahedral copper(II) complexes, the room temperature magnetic moment
values are usually observed in range of 1.8–2.2 B.M., which are not
affected appreciably by the temperature and the magnetic field. In the case
of planar, dimeric or polynuclear species, the complexes display sub-
normal magnetic moments. In practice, compounds whose geometry
approaches octahedral, usually exhibit magnetic moments which are at the
lower end, while those approaching tetrahedral geometry are at the higher
end. Reports are also available where square-planar[10,11] complexes have
magnetic moment in the range 1.8–2.2 B.M.
The magnetic moments of the present complexes (Table 3) fall within
the 1.87–2.05 B.M. range, usually reported for copper(II) complexes irres-
pective of the stereochemistry.[12] The magnetic moments are, therefore,
structurally non-diagnostic. These values also rule out any copper–copper
interactions.[13]
Electronic Spectra
Square-planar complexes commonly exhibit a broad structured band
from about 18,000 to 21,000 cm ꢀ 1 (555–475 nm)[14] while distorted-
octahedral copper(II) complexes usually show a broad d–d band in the

Mixed-Ligand Complexes of Copper(II)
677
Figure 2. Electronic spectrum of [Cu(DPA)(NICA)2] (1).
range[15] 11,000–17,000 cm ꢀ 1 (900–580 nm). The electronic spectra of
the present complexes show a broad d–d band with an absorption maxi-
mum located at 540–580 nm (18,518–17,241 cm ꢀ 1). These data suggest
that the present complexes represent a border line case of square-planar and
distorted octahedral complexes. The additional band of relatively high
intensity at 285–300 nm in theses complexes is assigned as ligand ! metal
charge transfer transition. The electronic spectrum of a representative com-
pound, [Cu(DPA)(NICA)2], is given in Figure 2.
Electron Spin Resonance Spectra
The room temperature X-band EPR spectrum of one representative
compound, [Cu(DPA)(o-PD)2], was recorded on a powdered sample using
the microwave frequency 9.45 GHz. Both parallel and perpendicular
features of 63Cu are not resolved in the spectrum of this compound. The
observed ‘g’ value of 2.067 which is less than 2.3, suggests the covalent
nature[16] of metal-ligand bonds in this complex. The ESR spectrum of this
compound is shown in Figure 3.
Infrared Spectra
The important IR spectral bands and their tentative assignments are
presented in Table 3. The strong bands at 1700 and 1450 cm ꢀ 1 in the spectrum

678
Maurya, Sharma, and Sutradhar
Figure 3. EPR spectrum of [Cu(DPA)(o-PD)2] (7).
of diphenic acid are assigned[1,6] as nas(C=O) and ns(C–O). The shifting of
these bands to lower wave numbers and appearing at 1588–1612 cm ꢀ 1 and
1376–1402 cm ꢀ 1 in the present complexes, suggests the coordination of
diphenic acid through its carboxylate anions. It is notable here that D values
[the difference between nas(C=O) and ns(C–O)] in the solid state vary smoothly
from 229–186 cm ꢀ 1 which fall within the range expected for a uni-
dentate[17,18] carboxylate ligand/group. The n(OH) band (observed at 3600–
3450 cm ꢀ 1 as a broad band) for free diphenic acid disappears upon co-
ordination, indicating that diphenic acid is a dibasic bidentate ligand co-
ordinating through both carboxylate anions. For the convenience of
interpretation, the present discussion of the IR data is divided into three parts.
NICA Complexes
The ligand NICA used in the present part of the discussion contains
two potential donor sites: 1) the pyridine ring nitrogen, and 2) the amide
oxygen. Significant IR spectral bands due to the amide group are n(NH),
n(CO) and n(CN). In amides[19] and other carbonyl donors,[20] a significant
shift to lower wave numbers of the n(CO) band takes place because of
coordination through the carbonyl oxygen. The n(NH), n(CO) and n(CN)
bands of free NICA remain almost unperturbed. These features clearly
indicate that the amide group does not coordinate.

Mixed-Ligand Complexes of Copper(II)
679
The characteristic ring vibration, n(C=N), of the free ligand at 1575
cm ꢀ 1 generally shows a significant shift to higher frequency in the com-
plexes. But in the present case this band could not be distinguished because
of overlapping with n(C=O) of the diphenic acid. However, the pyridine
breathing mode occurring at 990 cm ꢀ 1 in the free ligand undergoes a
significant shift to higher frequency and appears at 1021 cm ꢀ 1 in the
complex. This observation indicates the coordination of NICA via the pyri-
dine ring nitrogen[21] only.
CPY Complexes
The ligands 2-CPY, 3-CPY and 4-CPY used in the present study possess
two donor sites: 1) the pyridine ring nitrogen, and 2) the nitrile group. The
nitrile group may be involved in coordination either through the nitrogen or the
triple bond. Coordination through the nitrogen of the nitrile group[22]
invariably results in an increase in n(C=N) by at least 30 cm ꢀ1. A decrease
in n(C=N) is generally interpreted as resulting from the coordination of the
cyano group through its triple bond.[22] In the complexes of the cyanopyridines
studied here, the n(CN) band of the free cyanopyridines ( ꢃ 2235 cm ꢀ 1
)
remains the almost unchanged, thereby suggesting that the cyano group of
these ligands does not participate in coordination. However, the appearance of
a ring breathing mode at 1026–1040 cm ꢀ 1 in the complexes (2)–(4), suggests
the coordination of these ligands through the pyridine ring nitrogen.
o-TD, m-TD and o-PD Complexes
These three ligands possess only the amino nitrogen as donor site. The
appearances of two broad bands at 3331–3385 and 3100–3200 cm ꢀ 1 as-
signable to nas(NH) and ns(NH) suggest the coordination of the amino
nitrogen of these ligands to copper (Table 2).
Figure 4. Proposed square-planar structure of [Cu(DPA)(L)2] (L = NICA, 2-CPY,
3-CPY, 4-CPY, o-TD, m-TD or o-PD).

680
Maurya, Sharma, and Sutradhar
CONCLUSION
Satisfactory analytical data and all of the above results suggest the
formulation of these complexes as [Cu(DPA)(L)2], where L = NICA,
2-CPY, 3-CPY, 4-CPY, o-TD, m-TD or o-PD. Considering the unidentate
coordination of each of the carboxylate group of the diphenic acid ligand, a
square-planar structure, shown in Figure 4, is tentatively proposed for these
complexes. However, the electronic spectral results of these complexes in
dimethylformamide solutions (vide supra) probably suggest a tendency of
copper(II) square-planar complexes behaving as distorted octahedral com-
plexes (4 + 2 compounds) in solution.
ACKNOWLEDGMENTS
The authors are thankful to Professor S. D. Tripathi, Vice-Chancellor
of this University, for encouragement, and Professor K. K. Mishra, Head,
Department of Chemistry, for laboratory facilities and helpful discussion.
Analytical facilities provided by the Central Drug Research Institute, Luck-
now, India are gratefully acknowledged. Thanks are also due to Referee I,
for constructive suggestions.
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Received: August 17, 1998
Accepted: January 17, 2003
Referee I: J. D. Zubkowski
Referee II: M. A. Green