Copper(II) complexes of new tetradentate NSNO pyridylthioazophenol ligands: Synthesis, spectral characterization and crystal structure

Article abstract of DOI:10.1016/j.poly.2004.07.023

Copper(II) complexes of a series of new tetradentate NSNO ligands were synthesized and characterized spectroscopically. The ligands were also characterized by elemental analyses, IR, ¹H NMR, FAB-MS and UV-Vis spectroscopy. The solid-state structures of two complexes 2a and 4a were established by X-ray crystallography. The geometry about the copper ion of the complexes is dependent on the counter anion of the copper salt used. The five-coordinated copper ion is distorted square pyramidal when SCN^- or Cl^- ligate with the copper(II) ion, occupying the equatorial position, whereas the geometry about the four-coordinated copper ion is square planar when the counter anion is perchlorate. The electronic spectra of 2 and 3 in methanol show that the distortion of square pyramidal towards trigonal bipyramidal geometry about the copper ion of the complexes in solution is dependent on the presence of the electron withdrawing group. All the complexes exhibit a band for S(σ) → Cu(II) charge transfer (LMCT) in the range of 380-394 nm. The EPR spectra of complexes 2 and 3 are consistent with the fact that the unpaired electron is predominantly in the dx2-y2 orbital as g _II > g_I. The redox behavior of all the complexes in methanol was studied by CV using TBAP as the supporting electrolyte.

Full text of DOI:10.1016/j.poly.2004.07.023

Polyhedron 23 (2004) 2457–2464
www.elsevier.com/locate/poly
Copper(II) complexes of new tetradentate NSNO
pyridylthioazophenol ligands: synthesis, spectral
characterization and crystal structure
a
Pulak K. Dhara , Sadhan Pramanik , Tian-Huay Lu , Mike.G.B. Drew ,
a
b
c
a,
*
Pabitra Chattopadhyay
a
Department of Chemistry, The Burdwan University, Golapbag, Burdwan 713104, W.B., India
b
Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan, ROC
c
Department of Chemistry, Reading University, Reading RG 66AD, Berks, UK
Received 26 June 2004; accepted 16 July 2004
Available online 25 September 2004
Abstract
Copper(II) complexes of a series of new tetradentate NSNO ligands were synthesized and characterized spectroscopically. The
1
ligands were also characterized by elemental analyses, IR, H NMR, FAB-MS and UV–Vis spectroscopy. The solid-state structures
of two complexes 2a and 4a were established by X-ray crystallography. The geometry about the copper ion of the complexes is
ꢀ
dependent on the counter anion of the copper salt used. The five-coordinated copper ion is distorted square pyramidal when SCN
ꢀ
or Cl ligate with the copper(II) ion, occupying the equatorial position, whereas the geometry about the four-coordinated copper
ion is square planar when the counter anion is perchlorate. The electronic spectra of 2 and 3 in methanol show that the distortion of
square pyramidal towards trigonal bipyramidal geometry about the copper ion of the complexes in solution is dependent on the
presence of the electron withdrawing group. All the complexes exhibit a band for S(r) ! Cu(II) charge transfer (LMCT) in the
range of 380–394 nm. The EPR spectra of complexes 2 and 3 are consistent with the fact that the unpaired electron is predominantly
in the d
2
2
I
orbital as gII > g . The redox behavior of all the complexes in methanol was studied by CV using TBAP as the support-
x ꢀy
ing electrolyte.
ꢀ
2004 Elsevier Ltd. All rights reserved.
Keywords: Copper(II) complex; Pyridylthioazophenol ligands; Crystal structure
1
. Introduction
of a large number of metalloproteins having the CuN2S2
chromophore [1], has stimulated efforts to design new
ligand frames having nitrogen–sulfur donor sets and
characterize copper complexes as models for providing
a better understanding of the biological system [2]. It
has been found that copper(II) chelates, especially of
nitrogen–sulfur ligand frames, have antineoplastic activ-
ities and interactions with biological systems [3]. Consid-
erable attention has been directed towards the synthesis
of copper(II) chelates, especially of nitrogen–sulfur con-
taining ligands, in search of nuclear medicine [4] and
anticancer agents present in the hypoxic cell [5]. Again,
current research shows that the involvement of both the
The coordination chemistry of transition metal com-
plexes involving nitrogen and sulfur donor ligands has
been the cynosure among chemists during recent years
due to the application of these chelates in modelling of
biomolecules, in the field of chemical and biological
reactivity and nuclear medicine. The potential role
played by copper ions, being present in the active sites
*
Corresponding
913422530452.
E-mail address: pabitracc@yahoo.com (P. Chattopadhyay).
author.
Tel.:
+913422558339;
fax:
+
0
277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.07.023

2458
P.K. Dhara et al. / Polyhedron 23 (2004) 2457–2464
sulfur-to-copper charge transfer (LMCT) and the cop-
per d–d band in the photosensitization process lead to
an efficient DNA cleavage [6].
obtained from vibrating sample magnetometer PAR 155
model. X-band EPR spectra were taken on a Brucker
spectrometer with a variable temperature liquid nitrogen
Herein, we have synthesized three sets of copper(II)
complexes of a series of new tetradentate NSNO ligands
using different copper(II) salts. In this paper, we present
an account on copper(II) complexes of pyridylthioazo-
phenol ligands. The present contribution aims to study
the structural chemistry of the copper(II) complexes
of the new ligands and the change of the geometry about
cryostat at NTHU, Hsinchu, Taiwan. The values g and
II
AII were measured at 77 K. Electrochemical measure-
ments were made with a computer controlled EG&G
PAR model 270 VERSTAT electrochemical instrument
using Ag/AgCl electrodes. All measurements were made
at 298 K in dry MeOH with [Bu N]ClO as the support-
4
4
ing electrolyte. The experimental solutions were deoxy-
genated by bubbling with research grade dinitrogen.
The reported potentials are uncorrected for junction
potential.
ꢀ
the copper ion due to the presence of the anions (Cl ,
ꢀ
ꢀ
SCN and ClO4 ) in the copper salts. The complexes
and 3 are five-coordinated inner metallic complexes
where the fifth coordination number is satisfied by
2
ꢀ
ꢀ
NCS or Cl being present in the equatorial position
and the borderline base pyridine-N of the tetradentate
2.3. Syntheses of the ligands (HL)
(
NSNO) ligands are in the axial site of the distorted
square pyramidal geometry. In the cationic copper(II)
pyridylthioazophenol complexes (4), the counteranion
is perchlorate and the geometry about the copper ion
is square planar.
The syntheses of the ligands were carried out follow-
ing the common procedure of coupling different para-
substituted phenols with the diazotized 2-(2-pyridyl-
methylthio)-aniline (Scheme 1). The procedure for the
synthesis of 2-hydroxy-4-methyl-2 -(2-picolyl-thio)azo-
benzene (HL1) is as follows.
0
At first 2-(2-pyridylmethylthio)-aniline was synthe-
sized following the reported procedure [9]. Then the
preparation of 2-(2-pyridylmethylthio)-phenylazo-(4-
methyl)-phenolate was carried out. The details are given
as follows for 1a. To an alkaline solution of p-cresol
2
. Experimental
2
.1. Materials
All the reagents were obtained from commercial
(1.0 g, 9.3 mmol) at 5 ꢁC was added a diazotized solu-
sources and used without further purification. Cop-
per(II) thiocyanate was obtained by adding a saturated
solution of potassium thiocyanate to a solution of cop-
per(II) chloride in methanol, followed by removing the
precipitate of KCl by filtration. Tetra-n-butylammoni-
umperchlorate was prepared by the addition of sodium
perchlorate to a hot solution of tetra-n-butylammonium
bromide (Aldrich). The product was recrystallized from
aqueous ethanol and tested for the absence of bromide.
Solvents were distilled from an appropriate drying agent
tion of 2-(2-pyridylmethyl-thio)-aniline (2.0 g, 9.3
mmol) dropwise with continuous stirring. The tempera-
ture was controlled at ice-cold conditions. The resulting
solution was acidified and the pH was controlled be-
tween 6 and 7. The red colored compound so precipi-
tated was filtered and washed with water. Finally the
pure recrystallized compound was obtained from etha-
nol-water. The yield was 65%. The yield of the other lig-
ands varied from 50% to 68% following a similar
method. Anal. Calc. for 1a: C, 68.06; H, 5.07; N,
[
7].
1
1
2.53. Found: C, 68.83; H, 4.96; N, 12.74%. Calc. for
b: C, 70.02; H, 6.10; N, 11.14. Found: C, 69.63; H,
2
.2. Physical measurements
5.98; N, 11.54%. Calc. for 1c: C, 60.76; H, 3.94; N,
1.81. Found: C, 60.23; H, 3.81; N, 11.99%. Calc. for
1
1
The H NMR spectra were obtained on a Bruker
1d: C, 59.01; H, 3.82; N, 15.30. Found: C, 58.75; H,
3.75; N, 15.48%. Calc. for 1e: C, 71.16; H, 4.58; N,
11.32. Found: C, 70.92; H, 4.47; N, 11.56%; m.p.(ꢁC):
AC300 spectrometer with chemical shifts reported in d
values relative to the residual solvent resonance of
CDCl . IR spectra were obtained on a JASCO FT-IR
3
1a: 87 ± 1, 1b: 167 ± 1, 1c: 118 ± 1, 1d: 75 ± 1, 1e:
1
model 420 spectrometer using KBr disks, UV–Vis on a
JASCO UV–Vis/NIR model V-570 spectrometer and
mass spectra on a VG system, model 70-250S spectrom-
eter. Microanalyses were performed with the use of a
Perkin–Elmer 2400 CHN elemental analyzer and copper
analysis was carried out by the iodometric titration
method [8]. Molar conductance (K ) were measured in
a systronics conductivity meter 304 model using ꢁ10
M solutions in MeOH. Magnetic moments (l, BM) were
159 ± 1; H NMR d (ppm) (in CDCl ): 1a: 12.58(s,
3
1H), 8.52(d, 1H), 7.82–6.96 (m, 10H), 4.31(s, 2H),
2.31(s, 3H); 1b: 12.61(s, 1H), 8.54(d, 1H), 7.78–7.01
(m, 10H), 4.83(s, 2H), 1.40(s, 9H); 1c: 12.54(s, 1H),
8.50(d, 1H), 7.91–6.75 (m, 10H), 4.45(s, 2H); 1d:
12.61(s, 1H), 8.54(d, 1H), 8.01–6.96 (m, 10H), 4.50(s,
2H); 1e: 12.61(s, 1H), 8.51(d, 1H), 7.72–6.23 (m, 13H),
M
ꢀ
3
+
+
4.48(s, 2H); FAB-MS (FAB , [M+H] ): 1a: 336.11,
1b: 378.15, 1c: 356.06, 1d: 367.10, 1e: 372.12.

P.K. Dhara et al. / Polyhedron 23 (2004) 2457–2464
2459
Scheme 1. Synthetic procedure for the ligands.
2
.4. Syntheses of Cu(II) complexes of the ligands (HL)
C, 40.90; H, 2.46; N, 10.60; Cu, 12.03. Found: C,
0.64; H, 2.51; N, 10.79; Cu, 11.79%. Calc. for 4e: C,
4
The preparation follows a common procedure. To a
49.53; H, 3.00; N, 7.88; Cu, 11.91. Found: C, 50.04;
H, 2.88; N, 7.78; Cu, 11.51%.
methanolic solution (15 mL) of 1a (0.335 g, 1.0 mmol)
the corresponding copper salt (1.0 mmol) solution was
added dropwise and the resulting solution stirred for a
period of 3 h for 2a, 2 h for 3a and 4 h for 4a. The solu-
tion was dried at ambient temperature. The product was
2.5. X-ray crystal structure analysis
Single crystals suitable for X-ray work of 2a were
grown by slow evaporation of a solution of the complex
2a in methanolic:toluene (1:2) at ambient temperature
while 4a was grown by slow diffusion of hexane into a
benzene solution of the complex at 298 K. A suitable
single crystal of the complex 2a was mounted on a Bru-
ker SMART CCD diffractometer equipped with graph-
collected by washing with cold MeOH–H O and dried.
2
The pure reddish-violet colored crystallized product
was obtained from dichloromethane. Yield: 80–85%.
Anal. Calc. for 2a: C, 52.66; H, 3.69; N, 9.70; Cu,
1
4.67. Found: C, 52.01; H, 3.59; N, 9.91; Cu, 14.21%.
Calc. for 2b: C, 55.58; H, 4.63; N, 8.84; Cu, 13.36.
Found: C, 55.28; H, 4.50; N, 8.97; Cu, 12.98%. Calc.
for 2c: C, 47.63; H, 2.87; N, 9.26; Cu, 14.00. Found:
C, 48.01; H, 2.93; N, 9.31; Cu, 13.67%. Calc. for 2d:
C, 46.55; H, 2.80; N, 12.07; Cu, 13.68. Found: C,
6.76; H, 2.78; N, 12.19; Cu, 13.90%. Calc. for 2e: C,
6.29; H, 3.41; N, 8.96; Cu, 13.54. Found: C, 55.98;
H, 3.32; N, 8.98; Cu, 13.39%. Calc. for 3a: C, 52.69;
H, 3.51; N, 12.29; Cu, 13.94. Found: C, 52.12; H,
˚
ite monochromated Mo Ka (k = 0.71073 A) radiation.
The intensity data were corrected for Lorentz and polar-
ization effects and an empirical absorption correction
was also employed using the SAINT program. A total
of 10601 [unique data = 4107; Rint = 0.032] reflections
were measured and 2876 reflections were assumed ob-
served the applying the condition I > 2r(I). The struc-
ture was solved by Patterson syntheses, followed by
successive Fourier and difference Fourier syntheses. Full
4
5
3
4
.44; N, 12.51; Cu, 13.39%. Calc. for 3b: C, 55.48; H,
.42; N, 11.25; Cu, 12.76. Found: C, 55.98; H, 4.30;
2
matrix least squares refinements on F were carried out
N, 11.77; Cu, 12.18%. Calc. for 3c: C, 47.90; H, 2.73;
N, 11.76; Cu, 13.34. Found: C, 48.12; H, 2.83; N,
using SHELXL-97 with anisotropic displacement param-
eters for all non-hydrogen atoms in all cases. Hydrogen
atoms were constrained to ride on the respective carbon
atoms with an isotropic displacement parameter equal
to 1.2 times the equivalent isotropic displacement
parameter of their parent atom. The refinement con-
11.99; Cu, 13.69%. Calc. for 3d: C, 46.86; H, 2.67; N,
14.39; Cu, 13.05. Found: C, 47.01; H, 2.81; N, 14.89;
Cu, 12.79%. Calc. for 3e: C, 56.15; H, 3.25; N, 11.39;
Cu, 12.92. Found: C, 56.28; H, 3.30; N, 11.58; Cu,
1
1
2.39%. Calc. for 4a: C, 45.87; H, 3.22; N, 8.45; Cu,
2.78. Found: C, 46.03; H, 3.10; N, 8.71; Cu, 12.81%.
verged to residual indices R = 0.0390; wR = 0.0927 with
2
I > 2r(I). The final difference Fourier map showed the
maximum and minimum peak heights at 0.43 and
Calc. for 4b: C, 48.98; H, 4.08; N, 7.79; Cu, 11.78.
Found: C, 48.89; H, 4.06; N, 7.62; Cu, 11.57%. Calc.
for 4c: C, 41.74; H, 2.51; N, 8.11; Cu, 12.27. Found:
C, 41.95; H, 2.63; N, 7.95; Cu, 12.25%. Calc. for 4d:
ꢀ
3
˚
ꢀ0.27 e A , respectively, having no chemical signifi-
cance. Complex neutral atom scattering factors [10a]
were used throughout. All calculations were carried

2460
P.K. Dhara et al. / Polyhedron 23 (2004) 2457–2464
out using SHELXS-93 [10b], SHELXL-97 [10c], PLATON
-
9 [10d] and ORTEP3 [10e] programs. Data of 4a were
9
measured with Mo Ka radiation using the MARre-
search Image Plate System. The crystal was positioned
at 70 mm from the Image Plate. 100 frames were meas-
ured at 2ꢁ intervals with a counting time of 2 min. Data
analysis was carried out with the XDS program [11a] to
provide 2593 independent reflections. The structure
was solved using direct methods with the SHELX-86 pro-
gram [11b]. Non-hydrogen atoms were refined with
anisotropic thermal parameters. The hydrogen atoms
bonded to carbon were included in geometric positions
and given thermal parameters equivalent to 1.2 times
those of the atom to which they were attached. An
empirical absorption correction was applied using DI-
2
FABS [11c]. The structure was refined on F using
SHELXL [11d] with I > 2r(I).
Fig. 1. Solid-state structure of [Cu(L1)Cl] (2a) showing the atom
labelling scheme.
3
. Result and discussions
3
.1. Synthesis
The ligands 2-(2-pyridylmethylthio)-phenylazo-(4-
methyl)phenolates (1) were prepared by coupling 4-sub-
stituted-phenols with the diazonium ion obtained from
2
-(2-pyridylmethylthio)-aniline, which was synthesized
from 2-aminothiophenol by reacting it with 2-picolyl-
chloride in presence of a base at the first step. This series
of organic moieties act as tetradentate NSNO ligands
which are interesting chelators due to the presence of
hard donor azo-N and phenolate-O, borderline base
pyridine-N and soft thioether S donor centres. The lig-
ands have been spectroscopically characterized. The
copper(II) complexes of these ligands were obtained by
their reaction with equimolar amounts of the appropri-
ate copper salts in methanol. All the complexes are sol-
uble in common organic solvents.
Fig. 2. An ORTEP view of the cation of the complex 4a with thermal
ellipsoids at the 50% probability level and the atom numbering scheme.
˚
usual. The Cu–Cl bond distance is 2.2973(9) A. The
3
.2. Structures of the Cu(II) complexes (2a and 4a)
The ORTEP views of 2a and 4a are illustrated in
thioether sulfur S is strongly coordinated with copper,
being present in the basal plane, and the Cu–S bond dis-
˚
tance of 2.3360(8) A is shorter than axial [12] and mod-
Figs. 1 and 2, respectively, with the atom numbering
schemes shown. The selected bond distances and angles
are listed in Tables 1 and 2, respectively. The crystal of
erate in comparison to the usually observed basal Cu–S
bond distances in pentacoordinated copper complexes
[13]. The structure of 2a is almost regular square pyram-
idal as seen from the trigonality index [14] s of only
0.116 [s = (b ꢀ a)/60 where b = O–Cu–S = 172.95(6)0ꢁ
and a = N2–Cu–Cl = 165.99(7)ꢁ].
2
a is of the monoclinic system with the space group
P2 /n. In this monomeric complex 2a, the copper center
1
is bonded to a tetradentate monobasic NSNO donor
pyridylthioazophenolate organic moiety (L1) and a
monodentate chloride ligand. The coordination geome-
try is distorted square pyramidal with two nitrogen,
one oxygen and chlorine donor atoms occupying the ba-
sal plane. The pyridinic N(1) shows the axial contact at a
In the complex cation of [Cu(L1)]ClO (4a), Cu(II) is
4
located in the centre of a square planar environment and
the metal atom is bonded to four atoms of the ligand.
Here, both coordinating N atoms are at equivalent dis-
tances whereas this fact is different in the case of 2a. The
distortion from square planar geometry to tetrahedral
geometry is also observed as distances from the donor
atoms to the square plane are ꢀ0.29, 0.29, ꢀ0.27, 0.28
˚
long distance of 2.2194 (18) A. The axial Cu–N(1) bond
˚
distance (2.2194 (18) A) is longer than the equatorial
˚
Cu–N(2) (1.980 (2) A) due the geometric position as

P.K. Dhara et al. / Polyhedron 23 (2004) 2457–2464
2461
Table 1
Summarized crystallography data for 2a and 4a
Both complexes are monomeric but all the corre-
sponding Cu–O, Cu–N and Cu–S distances of 4a are sig-
nificantly shorter than those of 2a. It may be due to the
increase in formal charge on 2a by coordination of chlo-
ride and the difference in geometry of the complexes.
The Cu–N(pyridinic) distance in 4a is shorter than that
2
a
4a
Empirical formula
Formula weight
Crystal system
Space group
C
433.42
19
H
16ClCuN
3
OS
19 3 5
C H16ClCuN O S
497.40
monoclinic
C2/c
monoclinic
1
P2 /n
˚
of 2a by ca. 0.24 A. This Cu–N bond in 2a is axial and
˚
a (A)
9.8658(9)
8.6589(8)
21.6344(19)
90.00
26.15(3)
12.047(15)
14.179(15)
90.00
˚
not in the same plane as the other donor atoms of the
ligand, which is different from that in 4a. This difference
in bond lengths for the same ligand frame is due to the
flexibility of the Cu(II) coordination geometry.
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
99.224(2)
90.00
117.000(10)
90.00
˚
3
V (A )
calc (g/cm )
1824.3(3)
1.578
3981(8)
1.660
3
3.3. Spectral properties
q
Z
4
8
˚
Radiation wavelength k (A) 0.71073
0.71073
2024
293
The ligands 1 exhibit medium intense IR bands at
ꢀ1
F(000)
T (K)
884
293
ꢁ
3300 cm
(O–H of H bonded phenolic OH) [15]
which is absent in all the complexes. This indicates coor-
dination of oxygen to the metal centre [16]. The m
N@N
h (ꢁ)
l (Mo Ka) (mm
1.9–28.2
1.471
10601
2.22–25.98
1.471
5738
ꢀ1
)
ꢀ
1
Number of reflections
total)
Number of reflections
granted)
mode of the free ligand (1495–1505 cm ) is shifted to
1
ꢀ
(
lower to wave numbers (D ꢁ 20–30 cm ) in the com-
4107
2593
plexes, suggesting coordination of the metal ions to
the azo function [17]. The m
(
band is observed at
465–1478 cm for all the complexes. In addition to
N@N
Observed data (I > 2r(I))
R
2876
0.0390
0.0927
1914
0.1036
0.1347
ꢀ
1
1
ꢀ
1
wR
this m
cm for the complexes. Thiocyanato complexes 3 show
C–S
at 790 cm
for the ligands shifts to 760
ꢀ
1
ꢀ
1
a characteristic band in the range of 2050–2060 cm
indicating the presence of N-bonded NCS groups [18].
Infrared spectra of the complexes 4 exhibit an intense
band at approximately 1090 cm along with a weak
band at 625 cm which have been assigned to mðClOꢀÞ
The conductivity measurements of complexes 2 and 3
Table 2
˚
Selected bond distances (A) and bond angles (ꢁ) for 2a and 4a
ꢀ1
2a
4a
ꢀ1
.
Bond distances
Cu–O
4
1.9031(19)
1.980(2)
2.2194(18)
2.3360(8)
1.295(3)
1.359(3)
1.283(3)
1.440(4)
1.776(3)
1.812(3)
2.2973(9)
1.331(3)
Cu–O1
Cu–N9
1.860(9)
1.949(9)
Cu–N2
Cu–N1
Cu–S
in methanolic solution show the conductance in the
ꢀ1
Cu–N23
Cu–S16
O1–C2
1.984(10)
2.295(4)
ꢀ1
range of 9–20 K mol cm and those of 4 in MeOH
0
ꢀ1
ꢀ1
are 89–102 K mol cm . The values suggest that the
0
O–C18
N3–C13
N2–N3
N2–C12
S–C7
1.321(14)
1.388(15)
1.267(12)
1.420(15)
1.799(13)
1.852(13)
1.353(15)
1.340(16)
complexes 2 and 3 exist as non-electrolytes and 4 as hav-
ing 1:1 electrolytic nature in the solution state. Magnetic
susceptibility data reveal spin-only values for all the
copper complexes as the values are very close to 1.73
BM (in the range of 1.72–1.92 BM).
C7–N8
N8–N9 (azo)
N9–C10
C15–S16
S16–C17
C18–N23
C22–N23
S–C6
Cu–Cl
C1–N1
3
.3.1. Electronic spectra
The electronic absorption spectra of the azo ligands
Bond angles
N1–Cu–S
N1–Cu–N2
N1–Cu–Cl
N1–Cu–O
N2–Cu–S
N2–Cu–O
N2–Cu–Cl
Cl–Cu–S
81.80(6)
92.61(9)
98.95(6)
104.97(8)
85.96(7)
91.71(9)
165.99(7)
87.89(3)
92.89(6)
172.95(6)
128.79(18)
97.68(9)
O1–Cu–N9
O1–Cu–N23
N9–Cu–S16
N23–Cu–S16
O1–Cu–S16
N9–Cu–N23
C2–O1–Cu
N8–N9–Cu
N9–N8–C7
C10–N9–Cu
C15–S16–Cu
C17–S16–Cu
93.5(4)
96.9(4)
87.7(3)
and their complexes were recorded at room temperature
using MeOH as the solvent, and the results are shown in
Table 3. The spectra of the free ligands and the com-
plexes exhibit transitions at lower than 400 nm corre-
sponding to intramolecular p ! p* and n ! p*
transitions [19]. In the case of the complexes, a band
around 390 nm is assignable to the S(r) ! Cu(II)
charge transfer (LMCT) transition [6,20]. The cop-
per(II) complexes are characterized by a rather broad
d–d absorption band in their solution electronic spectra;
often a low- or high-energy shoulder is also present or,
occasionally, two distinct absorption maxima are ob-
served. In many cases it has been shown that the pres-
ence of a single d–d band with a high energy shoulder
86.2(3)
168.0(3)
157.8(4)
123.7(8)
128.1(8)
121.1(10)
114.5(7)
92.9(4)
Cl–Cu–O
O–Cu–S
N3–N2–Cu
C6–S–Cu
92.3(4)
˚
A for O(1), N(9), S(16) and N(23), respectively, the cop-
˚
per atom being ꢀ0.07 A from this plane. The perchlor-
ate ion has no close contact to the copper atom.

2462
P.K. Dhara et al. / Polyhedron 23 (2004) 2457–2464
Table 3
UV–Vis spectral, electrochemical and EPR data
0
3
ꢀ1
ꢀ1
ꢂ
Compound
k nm (e) (e, dm mol cm
)
Electrochemical data E ,
mV (DE , mV) [Epa, mV Epc, mV]
EPR data
p
g
II
A
II (G)
g
^
1a
1b
1c
1d
1e
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
206 (23385), 254 (11449), 326 (11871), 410 (7244),
58 (3981)
4
218 (24231), 252 (12658), 327 (10993), 408 (8012),
56 (3896)
4
210 (19952), 251 (10272), 320 (17102), 410 (7562),
72 (4265)
4
212 (21158), 236 (11322), 324 (8325), 412 (5822),
86 (3912)
4
212 (24271), 260 (12358), 308 (10986), 410 (4375),
94 (8522)
4
206 (24268), 260 (11415), 344 (11896), 392 (3854),
28 (6115), 708 (268), 852 (sh, 133)
ꢀ65 (150) [10, ꢀ140]
65.8 (148.3) [140, ꢀ8.3]
142.5 (93) [188, 95]
177 (96) [225, 129]
57.7 (150.6) [133, ꢀ17.6]
ꢀ13 (120) [47, ꢀ73]
50 (178) [139, ꢀ39]
130 (108) [184, 76]
165 (134) [232, 98]
62 (156) [140, ꢀ16]
15 (210) [120, ꢀ90]
69 (162) [150, ꢀ12]
120 (96) [168, 72]
2.229
2.234
2.230
2.221
2.237
2.231
2.232
2.227
2.217
2.238
164
166
160
154
168
167
172
165
158
173
2.054
2.060
2.052
2.052
2.058
2.040
2.041
2.043
2.037
2.045
5
218 (24550), 258 (13381), 346 (16544), 392 (5825),
28 (8182), 708 (270), 850 (sh, 111)
5
210 (16886), 260 (9837), 338 (7124), 386 (2967),
28 (4051), 718 (218), 844 (sh, 128)
5
216 (19982), 262 (10785), 330 (7253), 390 (2598),
28 (3925), 736 (186), 824 (193)
5
216 (23245), 258 (16284), 344 (4099), 386 (5127),
28 (8542), 700 (261), 896 (sh, 106)
5
206 (22931), 260 (7528), 346 (7531), 394 (2654),
28 (3804), 710 (198), 876 (sh, 97)
5
218 (26822), 258 (17102), 346 (15164), 392 (5165),
28 (8012), 710 (278), 875 (sh, 95)
5
208 (17089), 260 (10181), 344 (7201), 392 (3012),
28 (4212), 722 (172), 838 (sh, 92)
5
216 (19876), 262 (11108), 330 (7203), 390 (2501),
30 (4125), 730 (140), 820 (138)
5
216 (22956), 262 (16203), 338 (4322), 386 (5203),
30 (8433), 714 (201), 912 (sh, 65)
5
206 (29604), 260 (14038), 300 (9583), 346 (13671),
90 (5334), 530 (6890), 704 (317)
3
216 (25989), 261 (17223), 346 (15003), 390 (5324),
30 (8245), 706 (320)
5
208 (17522), 260 (10036), 342 (7112), 392 (4258),
30 (4549), 704 (318)
5
216 (19509), 262 (10798), 338 (6978), 391 (3122),
36 (5423), 708 (309)
152.5 (101) [203, 102]
63 (140) [133, ꢀ7]
5
216 (23203), 258 (16722), 339 (3949), 380 (5344),
36 (8738), 706 (321)
5
is typical of a trigonal bipyramidal stereochemistry for
copper, whereas an absorption with a low energy shoul-
der indicates a square pyramidal geometry [21].
On the basis of the above criterion, the observed data
of 2 and 3 suggest that the distortion of square pyram-
idal towards trigonal bipyramidal about the copper
ion of the complexes in solution is maximum in case
of the complexes 2d and 3d. Here, complexes 2d and
3d in methanol exhibit two bands of nearly equal inten-
sity between 730 and 824 nm, this pattern suggests that
the geometry about the copper ion in solution is between
square pyramidal and trigonal bipyramidal. In the case
of the complexes 4, only one broad d–d absorption band
around 705 nm and an intense band at 528 nm demon-

P.K. Dhara et al. / Polyhedron 23 (2004) 2457–2464
2463
Fig. 4. CV diagram of [Cu(L1)Cl] (2a) in MeOH.
4. Supporting material
Fig. 3. EPR spectra of [Cu(L1)Cl] (2a) in MeOH at 77 K.
Crystallographic data for the structural analyses have
strates the square planar geometry around the copper
ion.
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 229572 and 224745 for com-
pounds 2a and 4a, respectively. Copies of this informa-
tion are available free of charge on request from CCDC,
3
.3.2. EPR spectra
EPR spectra of the cupric complexes 2 and 3 have
1
1
2 Union Road, Cambridge, CB2 1EZ, UK (fax: +44
223 336 033; e-mail: deposit@ccdc.ac.uk or
been recorded in MeOH at 300 and 77 K. The data
are tabulated in Table 3 and one representative spectra
of 2a is shown in Fig. 3. However, the complexes in
the frozen state at 77 K show well-resolved peaks of
low intensities in the low-field region and an intense
peak in the high field region. No band corresponding
www:http://www.ccdc.cam.ac.uk).
Acknowledgements
to the M = +2 transition was observed in the spectra,
s
We thank the Department of Science and Technology
DST), New Delhi for financial assistance. M.G.B.
Drew thanks EPSRC and the University of Reading
for funds for the Image Plate system. The author
(P.C.) is indebted to Dr. C. Sinha, Department of Chem-
istry, B.U. for his valuable suggestions and discussions.
ruling out any Cu–Cu interaction. The complexes 2
and 3 appear to exhibit axial spectra of square pyrami-
dal species with g varying from 2.217 to 2.238 and A
(
II
II
ꢀ
4
ꢀ4
ꢀ1
having a range from 154 · 10 to 173 · 10 cm . The
result are in general agreement with the solution elec-
tronic spectra, which also suggest the existence of dis-
torted square pyramidal geometries with more
distortions in the complexes 2d and 3d. From the ob-
served g-tensor values of the Cu(II) complexes it is clear
that g > g which dictate that in complexes 2 and 3 the
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