Copper(II) complexes of thioarylazo-pentanedione: Structures, magnetism, redox properties and correlation with DFT calculations

Article abstract of DOI:10.1016/j.poly.2010.08.024

Copper(II) complexes of 3-((2-(alkylthio)phenylazo)-2,4-pentanedione, tridentate O, N, S donor ligands, are described in this work. Chloride bridged copper(II) polymers (1) and thiocyanato bridged copper(II) dimmers (2) are characterized by a single crystal X-ray diffraction study. The complexes show antiferromagnetic interactions, with J = -0.5 ± 0.1 cm^-1 (1a) and -25.8 ± 0.5 cm^-1 (2b), which implies stronger coupling in the -SCN-bridging compound. The spectra, redox and magnetism are explained by DFT studies.

Full text of DOI:10.1016/j.poly.2010.08.024

Polyhedron 29 (2010) 3147–3156
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Copper(II) complexes of thioarylazo-pentanedione: Structures, magnetism,
redox properties and correlation with DFT calculations
Mrinal Kanti Paira a, Tapan Kumar Mondal a, Elena López-Torres b, Joan Ribas c, Chittaranjan Sinha a,
⇑
a Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700 032, India
b Departamento de Química Inorgánica, c/Francisco Tomás y Valiente, 7. Universidad, Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
c Departament de Química Inorgànica, Universitat de Barcelona, Diagonal, 6487, 08028-Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Copper(II) complexes of 3-((2-(alkylthio)phenylazo)-2,4-pentanedione, tridentate O, N, S donor ligands,
are described in this work. Chloride bridged copper(II) polymers (1) and thiocyanato bridged copper(II)
dimmers (2) are characterized by a single crystal X-ray diffraction study. The complexes show antiferro-
magnetic interactions, with J = ꢀ0.5 0.1 cmꢀ1 (1a) and ꢀ25.8 0.5 cmꢀ1 (2b), which implies stronger
coupling in the –SCN-bridging compound. The spectra, redox and magnetism are explained by DFT
studies.
Received 16 November 2009
Accepted 7 August 2010
Available online 24 August 2010
Keywords:
Azoacetylacetonate
Copper(II) complex
Bridged dimer
Ó 2010 Elsevier Ltd. All rights reserved.
Antiferromagetic coupling
Spin density
1. Introduction
groups, –N@N– have assumed leading roles. The coordination
chemistry of transition metals with azo ligands is of interest due
Copper is second to iron in its usefulness in life and society. The
metal and its compounds are used in every sphere of life. The po-
tential role played by copper ions, present in the active sites of
many metalloproteins having the CuN2S2 chromophore [1–7], has
stimulated the design of new ligand frames having N, S donor sets
and their copper complexes as models for providing a better
understanding of biological systems [8–11]. The copper(II)-N,S
chelates have antineoplastic activities [12–20] and act as efficient
photosensitizers to cleave DNA [21,22]. The magnetic properties
of copper complexes, as discrete complexes and bridging dimers,
trimers, etc., are of great importance because of their potential
applications [23–25]. As a consequence, there has been continued
interest in the investigation of copper(II) complexes with the
to the observation of several interesting properties [34–38]. Azo
compounds are used as dyes and pigments. They exhibit antifungal
and antibacterial properties. The metal complexes of azo dyes
show more efficient activity than the organic molecules alone,
due to charge sharing and the availability of a binding site about
the metal ion, and have been put forward as photo-stable, weather
stable pigments [34–36]. Recently, some metal complexes of dyes
have found applications in photoelectronic devices, optical
recording media, light emitting diodes, field effect transistors,
photovoltaic cells (PVCs) [37,38,39–42], etc. The azo function is
photochromatic, induces easy charge transfer and exhibits intense
colour in the visible region. Compounds containing the azo group
are also pH-responsive and redox active [43–49,50]. In analytical
chemistry, azo compounds have been used as acid–base and metal-
lochromic indicators [51–55]. Some of them play a role as efficient
and selective spectrophotometric reagents, colorants in textile
industry and have been used in solid phase extraction processes
½CuI2Ið
l
-XÞ2ꢁ (X = Clꢀ, Brꢀ, N3ꢀ, SCNꢀ, etc.) core which display differ-
ent structures with a variety of Cu–X bond distances and Cu–X–Cu
bridge angles, depending on the type of terminal donor atoms and
other structure varying parameters [26,27].
The metal complexes of O, N and S donor ligands has expanded
enormously [28–33] and embraces very wide and diversified sub-
jects comprising vast areas of organometallic compounds and cat-
alysts, various aspects of bioinorganic chemistry, metal clusters,
supramolecular complexes, etc. In the development of the coordi-
nation chemistry of N-donor centers, imine, –N@C– and azo
[56–59]. The p-acidity and metal binding ability of the azo nitro-
gen have drawn interest to the exploration of the chemistry of me-
tal complexes incorporating azo ligands. Thus, the synthesis of
ligands incorporating the azo function in different backbones is
an inspiring field of research. We have been engaged for last dec-
ade in the design of azo-conjugated ligands and characterization
of their metal complexes [50,56–59,60,61,62–65,66]. Acetylace-
tone has an active –CH2– group and undergoes electrophilic
substitution by the diazonium ion, Ar-N@N–, to synthesise azo
⇑
Corresponding author.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.08.024

3148
M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
compounds. Because of the potential application of acetylacetona-
to metal chelates, chemists are trying to synthesize newer deriva-
tives and their complexes. Arylazo appended acetylacetone has
been known in the literature since 1925 [67–69]. However, thio-
arylazo (R–S–C6H4–N@N–) functionalized acetylacetone is hitherto
unknown. We have undertaken a programme to synthesise, 3-((2-
(alkylthio)phenylazo)-2,4-pentanedione, and then to synthesise
copper(II) complexes with this compound as a ligand. In some
cases the structures were confirmed by a X-ray diffraction study.
Variable temperature magnetic measurements were carried out
to explain the magnetic interactions present in the complexes.
The electronic, redox and magnetic properties are explained by
DFT computation using an optimized geometry for the complexes.
1506, 1357, 1319. 1H NMR data in CDCl3 (d, ppm): 15.05 (OH, s),
7.78 (11-H, d, J = 8.1 Hz), 7.49 (8-H, d, J = 7.2 Hz), 7.35 (9-H, t,
J = 7.7 Hz), 7.16 (10-H, t, J = 7.2 Hz), 2.63 (1-CH3, s), 2.51 (5-CH3,
s), 2.47 (12-CH3, s). 13C NMR data in CDCl3 (d, ppm): 197.1 (2-C),
196.9 (4-C), 122.1–142.7 (ArC, 6C), 115.1 (3-C), 30.2 (1-C), 26.3
(5-C), 24.3 (12-C). kmax
(e
ꢂ 10ꢀ3, Mꢀ1 cmꢀ1): 397 (18.3); 380
(21.3); 275 (8.82); 253 (15.0) in CHCl3.
2.1.1.2. 3-(2-(Ethylthio)phenylazo)-2,4-pentanedione, HL2. 2-(Ami-
no)-thioethylphenol was first synthesized following the above
mentioned method using 3.0 g (0.024 mol) 2-(amino)thiophenol
and 1.92 ml (0.024 mol) of EtI followed by coupling with 2.44 ml
(0.024 mol) acetylacetone. A yellowish orange precipitate was ob-
tained; it was filtered and washed with cold water, dried over
CaCl2 desiccators. Yield 4.95 g (78.1%), m.p. 101 °C. Microanalytical
data: Anal. Calc. for C13H16N2O2S: C, 59.05; H, 6.10; N, 10.59.
2. Experimental
Found: C, 59.20; H, 6.08; N, 10.43%. IR data (KBr disc) (m
, cmꢀ1):
2.1. Materials and measurements
1673(s), 1627(m), 1507, 1358, 1321. 1H NMR data in CDCl3 (d,
ppm): 15.07 (OH, s), 7.80 (11-H, d, J = 8.2 Hz), 7.53 (8-H, d,
J = 7.6 Hz), 7.40 (9-H, t, J = 7.7 Hz), 7.15 (10-H, t, J = 7.5 Hz), 2.80
(12-CH2, q, J = 14.6 Hz), 2.64 (1-CH3, s), 2.52 (5-H, s), 1.25 (13-
CH3, t, J = 7.3 Hz). 13C NMR data in CDCl3 (d, ppm): 197.3(2-C),
197.1 (4-C), 122.7–143.0 (ArC, 6C), 115.3 (3-C), 31.5 (12-C), 30.0
Acetylacetone (Hacac), 2-aminothiophenol, iodomethane (MeI),
iodoethane (EtI), CuCl2, 2H2O and NH4SCN were purchased from E.
Merck, India. All other chemicals used were of A.R. quality and
were used as received. The organic solvents were purified and
dried by standard methods [70]. The 2-(alkylthio)anilines were
prepared by a reported procedure [71].
(1-C), 26.6 (5-C), 14.7 (13-C). kmax
(14.3); 374 (17.6); 277 (5.63); 253 (12.6) in CHCl3.
(
e
ꢂ 10ꢀ3, Mꢀ1 cmꢀ1): 396
UV–Vis spectra were recorded using a Perkin–Elmer Lambda 25
UV–Vis spectrophotometer and infrared spectra were obtained
from a Perkin–Elmer Spectrum RX1 instrument. Microanalyses
were collected on a Perkin–Elmer 2400 CHN elemental analyser.
1H NMR spectra were recorded on a Brucker 300 MHz FT-NMR.
The room temperature magnetic moments were measured using
a Magnetic Susceptibility Balance, Sherwood Scientific Cambridge,
UK. Molar conductances (KM) were measured in a Systronics con-
ductivity meter 304 model using ca. 10ꢀ3 M solutions in acetoni-
trile. Electrochemical measurements were performed using
computer-controlled PAR model 250 VersaStat electrochemical
instruments with Pt-disk electrodes. All measurements were car-
ried out under a nitrogen environment at 298 K with reference to
SCE in acetonitrile using [nBu4N][ClO4] as the supporting electro-
lyte. The reported potentials are uncorrected for the junction po-
tential. EPR spectra were measured in MeCN–CH2Cl2 solution at
room temperature (298 K) and at liquid nitrogen temperature
(77 K) using a Bruker EPR spectrometer model EMX 10/12, X-band
ER 4119 HS cylindrical resonator.
2.1.2. Preparation of 1/n[Cu(L1)Cl]n (1a)
HL1 (92.6 mg, 0.37 mmol) was dissolved in methanol (20 ml)
and was added to a methanolic solution of CuCl2ꢃ2H2O (65.2 mg,
0.38 mmol) with stirring at room temperature and the stirring
was continued for 1 h. The colour of the solution changed from or-
ange yellow to blue green. The solution was then filtered and kept
for crystallization after the addition of a few drops of DMF. Block
shape crystals appeared on the inner wall of the beaker and were
collected by filtration, washed with MeOH–water (1:1, v/v) and
dried over CaCl2 in a desiccator. Yield, 98 mg (76%). Microanalytical
data: Anal. Calc. for C12H13N2O2SClCu: C, 41.38; H, 3.76; N, 8.04.
Found: C, 41.29; H, 3.85; N, 8.00%. IR data (KBr disc) (m
, cmꢀ1):
1657, 1364, 305. kmax
(10.418); 290 (8.039); 268 (10.981) in CHCl3.
(
e
ꢂ 10ꢀ3, Mꢀ1 cmꢀ1): 608 (0.420); 405
2.1.3. Preparation of 1/n[Cu(L2)Cl]n (1b)
The complex 1b was prepared following the same procedure as
1a using 100.3 mg (0.38 mmol) of HL2 and 65.2 mg (0.38 mmol) of
CuCl2ꢃ2H2O. Yield, 101 mg (73%). Microanalytical data: Anal. Calc.
for C13H15N2O2SClCu: C, 43.09; H, 4.17; N, 7.73. Found: C, 43.00;
2.1.1. Preparation of the ligands
2.1.1.1. 3-(2-(Methylthio)phenylazo)-2,4-pentanedione, HL1. Into a
50 ml ethanol solution of 2-(amino)thiophenol (2.9 g, 0.023 mol),
metallic sodium (0.534 g, 0.023 mol) was slowly added under cold
conditions, stirring with a magnetic stirrer. Stirring was continued
for 1 h, maintaining the cold conditions, whereupon the colour
changed from yellow to orange. Then 1.45 ml (0.023 mol) of MeI
was added under the same conditions, and the stirring was contin-
ued for 30 min. The mixture was then refluxed for 2 h at 65–70 °C
in a water bath, and the colour of the solution changed to red. The
whole mixture was then poured into a large excess of water, a
gummy mass separated out, and it was extracted in benzene and
washed with water. The benzene was then removed by a rotary
evaporator. The gummy mass was then dissolved 1:1 in HCl, and
NaNO2 solution was added dropwise to it at 0–5 °C. This solution
was then added to a Na2CO3 solution of acetylacetone (2.34 ml,
0.023 mol) dropwise. A yellowish orange precipitate was obtained;
it was filtered and washed with cold water, dried over CaCl2 desic-
cators. Yield 4.80 g (82.6%), m.p. 121 °C. Microanalytical data: Anal.
Calc. for C12H14N2O2S: C, 57.58; H, 5.64; N, 11.19. Found: C, 57.44;
H, 4.20; N, 7.80%. IR data (KBr disc) (m
, cmꢀ1): 1652, 1355, 308. kmax
(
e
ꢂ 10ꢀ3, Mꢀ1 cmꢀ1): 607 (0.529); 406 (14.493); 289 (11.024); 267
(15.109) in CHCl3.
2.1.4. Preparation of [Cu(L1)(SCN)]2 (2a)
To a CuCl2ꢃ2H2O solution (85.3 mg, 0.50 mmol) in methanol
(15 ml), HL1 (121.3 mg, 0.49 mmol) was added in same solvent
(15 ml MeOH) and the mixture was stirred for 30 min. Then
NH4SCN (938.3 mg, 0.50 mmol) in MeOH solution was added and
the stirring was continued for another 2.5 h, whereupon the colour
of the solution changed to greenish yellow. The solution was fil-
tered and kept for crystallization, after the addition of few drops
of DMF, by slow evaporation in air. A crystalline product was ob-
tained within 3 days. The crystals were collected and washed with
MeOH–water (1:1, v/v) and dried over CaCl2 in a desiccator. Yield
127 mg (71%). Microanalytical data: Anal. Calc. for C26H26N6O4S4-
Cu2: C, 42.09; H, 3.53; N, 11.33. Found: C, 42.00; H, 3.50; N,
11.28%. IR data (KBr disc) (m
, cmꢀ1): 2110, 1659, 1356. kmax
(
e
ꢂ 10ꢀ3, Mꢀ1 cmꢀ1): 599 (0.337); 420 (15.40), 374 (16.816);
H, 5.67; N, 11.06%. IR data (KBr disc) (
m
, cmꢀ1): 1671(s), 1626(m),
327 (5.711); 278 (6.380) in CHCl3.

M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
3149
2.1.5. Preparation of [Cu(L2)(SCN)]2 (2b)
factors and anomalous dispersions factors are contained in the
SHELXTL 6.10 program library.
Complex 2b was prepared following the procedure of 2a using
132.0 mg (0.50 mmol) of HL2, 85.3 mg (0.50 mmol) CuCl2ꢃ2H2O
and 938.3 mg (0.50 mmol) of NH4SCN in MeOH. Yield 135 mg
(72%). Microanalytical data: Anal. Calc. for C28H30N6O4S4Cu2: C,
43.68; H, 3.93; N, 10.91. Found: C, 43.65; H, 3.95; N, 11.00%. IR data
2.3. Variable temperature magnetic measurements
The magnetic behavior of [Cu(L1)Cl]n (1a) and [Cu(L2)(SCN)]2
(2b) were measured on a SQUID susceptometer in the temperature
range 2–300 K and with a magnetic field value of 0.1 T. Diamagne-
tism was corrected from Pascal Tables. Magnetization measure-
ments were made in the same SQUID at 2 K.
(KBr disc) (
m
, cmꢀ1): 2114, 1660, 1356. kmax
(e
ꢂ 10ꢀ3, Mꢀ1 cmꢀ1):
616 (0.630); 407 (13.217); 295 (10.760); 270 (13.041) in CHCl3.
2.2. Crystal structure determination
The crystals, [Cu(L1)Cl]n (1a) (0.15 ꢂ 0.20 ꢂ 0.30 mm), [Cu(L2)-
(NCS)]2 (2b) (0.15 ꢂ 0.30 ꢂ 0.30 mm) were grown by slow evapo-
ration of the reaction mixture in methanol over a week. Data were
collected (Table 1) using a Bruker AXS Kappa Apex-II diffractome-
ter equipped with an Apex-II CCD area detector using a graphite
2.4. Computation
Full geometry optimizations of the complexes were carried out
using the density functional theory method at the (U)B3LYP level
[76–78]. All elements except Cu were assigned the 6-31G(d) basis
set. LanL2DZ with an effective core potential for a Cu atom was used.
The vibrational frequency calculations were performed to ensure
that the optimized geometries represent the local minima and that
there are only positive eigen values. All calculations were performed
with GAUSSIAN03 program package [79] with the aid of the GaussView
visualization program [80]. Vertical electronic excitations based on
B3LYP optimized geometries were computed using the time-depen-
dent density functional theory (TD-DFT) formalism [81–83] in chlo-
roform using a conductor-like polarizable continuum model (CPCM)
[84–86]. GaussSum [87] was used to calculate the fractional contri-
butions of various groups to each molecular orbital.
monochromator (Mo Ka radiation, k = 0.71 073 Å). Diffractions
were recorded with 2h in the range 4.62 6 2h 6 57.40° for 1a and
2.96 6 2h 6 57.40° for 2b. Reflection data were recorded using
the
w and x scan techniques. Data were corrected for Lp and an
empirical absorption correction in the hkl range: ꢀ14 6 h 6 14;
ꢀ23 6 k 6 23; ꢀ10 6 l 6 10 for 1a and ꢀ17 6 h 6 17; ꢀ19 6 k 6
19; ꢀ19 6 l 6 19 for 2b. The substantial redundancy in data allows
empirical absorption corrections (SADABS) [72] to be applied using
multiple measurements of symmetry-equivalent reflections. The
raw intensity data frames were integrated with the SAINT program,
which also applied corrections for Lorentz and polarization effects.
[73] The software package SHELXTL version 6.10 was used for space
group determination, structure solution and refinement. The struc-
tures were solved by direct methods (SHELXS-97), [74] completed
with difference Fourier syntheses, and refined with full-matrix
3. Results and discussion
3.1. Synthesis and formulation
least squares using SHELXL-97 minimizing
x
ðF20 ꢀ F2c ). Weighted R
factors (Rw) and all goodness of fit S are based on F2; conventional
R factors (R) are based on F [75]. All non-hydrogen atoms were re-
fined with anisotropic displacement parameters and hydrogen
atoms were located by difference maps, although they were posi-
tioned geometrically after each cycle of refinement. All scattering
The 3-(2-(alkylthio)-2-phenylazo)-2,4-pentanediones (R = Me,
HL1; Et, HL2) are synthesized by coupling 2-(alkylthio)phenyldiazo-
nium chloride with acetylacetone in basic medium (Na2CO3
solution, pH 7) (Scheme 1) and are purified by repeated crystallisa-
tion from an aqueous ethanol (1:1, v/v) mixture. The purity of the
product was checked by elemental analyses.
The reaction between a methanolic solution of CuCl2ꢃ2H2O and
Table 1
Crystallographic data of [Cu(L1)Cl]n (1a) and [Cu(L2)(SCN)]2 (2b).
HL in a 1:1 mole ratio has isolated shining dark green crystals of
Crystal parameter
(1a)
(2b)
13
12
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C
12H13ClCuN2O2S
C28H30Cu2N6O4S4
769.90
12
S
8
348.29
monoclinic
P2(1)/c
8
S
S
triclinic
9
9
7
7
ꢀ
N
P
6
6
O
10
10
N
N
OH
10.7980(4)
17.6826(7)
7.4096(3)
90.00
109.201(2)
90.00
1336.06(9)
0.71073
1.732
12.9475(11)
14.1966(12)
14.2019(11)
76.541(4)
88.561(4)
66.165(4)
2315.3(3)
0.71073
1.657
N
N
OH
11
11
b (Å)
c (Å)
4
4
5
5
3
3
a
(°)
b (°)
2
2
c
(°)
O
1
O
1
V (Å3)
k (Å)
1
2
HL
HL
qcalcd (Mg mꢀ3
)
Z
4
708
1.988
100(2)
14 853
3432
3
R
R
F(0 0 0)
l
T (K)
Total data
1182
1.694
296
103 922
11 880
604
0.0470
0.1431
1.09
SCN
(mmꢀ1
)
S
Cl
S
Cu
Cu
Cl
2
Unique data
n
N
N
N
O
O
Refined parameters
224
Ra
0.0232
0.0608
1.057
N
wRb
GOF
CH
3
H
C
O
O
3
a
R =
wR2 = [
R
||F0| ꢀ |Fc||/
R|F0|.
P
2
2 1=2
wðF20 ꢀ Fc2Þ = wðF02Þ ꢁ
, w = 1/[r
2(F0)2 + (0.0258P)2 + 0.9848P] for
b
2; R = Me ( a), Et (b)
R
1
[Cu(L1)Cl]n (1a); w = 1/[
where P ¼ ðF20 þ 2Fc2Þ=3.
r
2(F0)2 + (0.0682P)2 + 6.9845P] for [Cu(L2)(SCN)]2 (2b);
Scheme 1. The ligands and the complexes.

3150
M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
[Cu(L)Cl]n (1). The reaction of CuCl2ꢃ2H2O, HL and NH4SCN in a
1:1:2 mole ratio has isolated [Cu(L)(NCS)]2 (2). The composition
of the complexes is supported by microanalytical data. The com-
plexes are sufficiently soluble in chloroform, dichloromethane,
acetonitrile, DMF and DMSO, but are insoluble in hexane, benzene
and toluene. They are non-conducting in solutions of acetonitrile,
DMF, etc. At room temperature the effective magnetic moments
are 1.73 (1a), 1.80 (1b), 1.60 (2a) and 1.55 BM (2b) per copper cen-
tre. The subnormal moment may be due to magnetic exchange be-
tween Cu(II) (d9) centres via bridging Cl or NCS ligands.
and inferred the presence of 100% enolic, –(C@C–)–OH, hydrogen.
Two –CH3 groups of the acetylacetonyl part appear at 2.51 and
2.63 ppm. The thioalkyl group, –S–R, appears at its usual position:
–S–Me, 2.47 ppm; –S–CH2–CH3, 2.80 (14.6 Hz) (–CH2–) and 1.25
(7.3 Hz) (–CH3) ppm.
3.3. Molecular structures
3.3.1. [Cu(L1)Cl]n (1a)
The unit structure of 1a is shown in Fig. 2. Selected bond lengths
and angles are listed in Table 2 (detailed metric parameters are gi-
ven in Table S1 in the Supplementary material). The coordination
environment around copper is of the –Cu(O,N,S)Cl2 type. The li-
gand HL1 acts as a tridentate monoanionic N,O,S donor system
(azo-N, enolato-O and thioether S-Me donor centres). Cl acts as
bridge and forms the –Cl–Cu(O,N,S)–Cl– motif in which Cl bridges
axially to a neighbouring [Cu(O,N,S)Cl], and forms a 1-D chain. The
bond parameters suggest a distorted square pyramidal geometry
around the copper center. The basal plane (mean deviation
<0.03 Å) is constituted by [Cu(O,N,S)Cl]. Two chelate planes,
Cu(1), N(1), N(2), C(7), C(8), O(1) and Cu(1), N(1), C(6), C(1), S(1),
3.2. Spectral studies
Infrared spectra of the ligands (HL) exhibit a large number of
vibrations and significant frequencies are
1410 and 1670 cmꢀ1, respectively. In the complexes the bands at
1375–1390 and 1630–1645 cmꢀ1 are assigned to
(N@N) and
m(N@N) and m(C@O) at
m
m
(C@O), respectively. The most significant observation in the IR
spectra of 2 is the strong stretching at 2110–2115 cmꢀ1 which is
assigned to bridging –NCS– in the complexes [88,89].
The electronic spectra of HL are recorded in chloroform because
of the sparing solubility of the complexes in DMF solution. The spec-
tra of the ligands show two significant transitions at 250–255 and
370–380 nm with two shoulders at 275–280 and 390–400 nm, that
show only small distortions and make
a dihedral angle of
5.71(5)°. The Cu–N(azo) distance (1.9479(13) Å) is comparable
with previously reported data [66,90–92]. The Cu–S distance is
2.2807(5) Å. The bridging Cuꢃ ꢃ ꢃCl is ꢄ0.6 Å longer than the normal
Cu–Cl distance (normal Cu–Cl, 2.2643(4) Å, bridging Cuꢃ ꢃ ꢃCl,
2.8365(5) Å). The Cu–S bond distance is 2.2807(5) Å, which is in
the reported range [90–92]. The N@N distance is 1.2784(18) Å. We
do not have free ligand bond length data to compare with the elec-
tronic delocalization in the complexes. However, on comparing with
the structure of 1-alkyl-2-(arylazo)imidazole [50a] we have as-
sumed that the N@N distance is significantly longer (free ligand
data, 1.26 Å), which may be due to charge delocalization from Cu(II)
are assigned to
complexes exhibit high intense transitions (
p–p p
* and n– * transitions. The spectra of the
e
ꢄ 104 Mꢀ1 cmꢀ1) in
the 400–420 nm range along with a moderately intense band at
600–620 nm (
e
ꢄ 400–650 Mꢀ1 cmꢀ1). Intraligand charge transfers
(n– p–p
p
* and *) appear <400 nm (Section 2, Fig. 1). The coordination
of –SR to CuII enhances the probability of d(Cu) ?
p
*(azoimidazole)
charge transfer [8–11,12,13] and shifts the band maxima to a longer
wavelength compared to that of [Cu(azoimidazole)2(X)2] com-
plexes. On comparing with reported results [90–92] of N, S donor
ligands, the transition at 400-420 nm may be assigned to a mixture
to the p-acidic azo group. The pendant –CO–(CH3) oxygen forms a
hydrogen bonding interactions (given in Table S2 vide Supplemen-
tary material) and enhances the rigidity of the supramolecularstruc-
ture [C(2)–H(2)ꢃ ꢃ ꢃO(2):H(2)ꢃ ꢃ ꢃO(2), 2.49(2) Å; C(2)ꢃ ꢃ ꢃO(2), 3.355(2)
Å; \C(2)–H(2)ꢃ ꢃ ꢃO(2), 164.4(17)° (symmetry: 1 + x, y, 1 + z). C(12)–
H(12C)ꢃ ꢃ ꢃO(2):H(12C)ꢃ ꢃ ꢃO(2), 2.57(2) Å; C(12)ꢃ ꢃ ꢃO(2), 3.353(2) Å;
\C(12)–H(12C)ꢃ ꢃ ꢃO(2), 143.1(18)°].
*
p (azoimidazole) and S(p) ? Cu(II) transitions. The
of d(Cu) ?
weak absorption at 595–620 nm is undoubtedly a d–d transition.
The 1H NMR spectra of the ligands are recorded in CDCl3. The
Cu(II) complexes are paramagnetic and the 1H NMR spectra are
not recorded. Data of the ligands are given in Section 2 and the
assignments have been made on the basis of spin–spin interac-
tions. The atomic numbering for the structures is given in Scheme
1. HL may exist in the keto-enol tautomeric form; a sharp reso-
nance is observed at 15.05 ppm that is assigned to an –OH group.
The intensity of d(OH) was compared with signals of other protons
3.3.2. [Cu(L2)(NCS)]2. (2b)
The X-ray structure (Fig. 3) reveals that the complex 2b is a neu-
tral thiocyanato bridged copper(II) dimer. Selected bond lengths
2.0x104
1200
900
1.5x104
600
300
1.0x104
0
500
600
700
800
900
Wavelength (nm)
5.0x103
0.0
300
400
500
600
700
800
Wavelength (nm)
Fig. 1. UV–Vis spectra of HL2(–), [Cu(L2)Cl]n (1b) (–) and [Cu(L2)(SCN)]2 (2b) (–) in
CHCl3. Low energy band of [Cu(L2)Cl]n (1b) (–) and [Cu(L2)(SCN)]2 (2b) (–) shown in
the insert picture.
Fig. 2. Ortep plot of [Cu(L1)
l-Cl]n (1a) (H-atoms are omitted for clarity).

M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
3151
Table 2
Bond distances and bond angles.
Bond lengths (Å)
Bond angles (°)
X-ray
DFT
X-ray
DFT
[Cu(L1)Cl]n (1a)
Cu(1)–Cl(1)
Cu(1)–S(1)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–Cl(1b)
N(1)–N(2)
2.2643(4)
2.2807(5)
1.9271(13)
1.9479(13)
2.8365(5)
1.2784(18)
2.278
2.326
1.930
1.954
–
Cl(1)–Cu(1)–S(1)
Cl(1)–Cu(1)–O(1)
Cl(1)–Cu(1)–N(1)
Cl(1)–Cu(1)–Cl(1b)
S(1)–Cu(1)–O(1)
S(1)–Cu(1)–N(1)
O(1)–Cu(1)–N(1)
88.06(2)
93.40(4)
174.10(4)
103.08(1)
167.50(4)
87.06(4)
90.65(5)
90.43
94.40
168.2
–
168.5
87.65
89.67
1.289
[Cu(L2)(SCN)2]2 (2b)
Cu(1)–S(1)
Cu(1)–S(2)
Cu(1)–O(1)
Cu(1)–N(1)
Cu(1)–N(6)
Cu(2)–S(3)
Cu(2)–S(4)
Cu(2)–O(3)
Cu(2)–N(3)
Cu(2)–N(4)
N(1)–N(2)
2.3588(9)
2.6468(10)
1.956(2)
1.933(3)
1.932(3)
2.3230(9)
2.8088(9)
1.938(2)
1.952(3)
1.934(3)
1.282(3)
1.289(4)
2.49003
2.80135
2.03427
1.90819
1.84951
2.46138
2.92318
2.00338
1.85792
1.90798
1.28718
1.28691
S(1)–Cu(1) –S(2)
S(1)–Cu(1) –O(1)
S(1)–Cu(1) –N(1)
S(1)–Cu(1) –N(6)
S(2)–Cu(1) –O(1)
S(2)–Cu(1) –N(1)
S(2)–Cu(1) –N(6)
O(1)–Cu(1) –N(1)
O(1)–Cu(1) –N(6)
N(1)–Cu(1) –N(6)
S(3)–Cu(2) –S(4)
S(3)–Cu(2) –O(3)
S(3)–Cu(2) –N(3)
S(3)–Cu(2) –N(4)
S(4)–Cu(2)–O(3)
S(4)–Cu(2)–N(3)
S(4)–Cu(2)–N(4)
101.42(3)
150.23(8)
85.70(8)
93.58(9)
107.78(8)
88.67(8)
94.36(8)
89.24(11)
89.94(12)
176.96(11)
85.21(3)
169.68(8)
92.70(8)
87.04(8)
104.60(7)
93.97(8)
86.58(8)
98.85229
152.32424
85.62552
92.21789
107.88309
87.26765
96.31118
88.57363
91.84358
176.07654
86.14518
168.92936
91.63577
86.69494
104.16889
96.66019
89.37554
N(4)–N(5)
and angles are given in Table 2 (detailed metric parameters are gi-
ven in Table S1 in the Supplementary material). The copper lies in a
distorted square pyramid with CuON2S2 donor sets. There are two
dimers in the unit cell. The dimer is generated by two –NCS– bridges.
The bridge angles are N(3)–Cu(2)–S(4), 93.96(8)°, and N(6)–Cu(1)–
S(2), 94.35(9)°. The –NCS– unit is almost linear, as is revealed from
the angles N(3)–C(14)–S(2), 179.1(3)° and N(6)–C(28)–S(4),
178.0(3)°. The chelate angles are \O(1)–Cu(1)–N(1), 89.23(10)°
and \N(1)–Cu(1)–S(1), 85.70(8)°. The two chelate planes, Cu(1),
N(1), N(2), C(7), C(8), O(1) and Cu(1), N(1), C(1), C(6), S(1), are not
planar and make a dihedral angle of 19.37°. The distorted square
plane is constituted by CuON2S, on which the bridged thiocyanato-
S lies perpendicular (ꢄ94°). There are two N donor centres: N(azo)
and N(thiocyanato), and the Cu–N distances lie within the range
1.889–1.953 Å. The two S donor centres show different Cu–S dis-
tances: the chelated thioether-S shows lower Cu–S distances
(2.32–2.36 Å) than that of Cu–S(thiocyanate) (2.64–2.81 Å). The
N@N distances are N(1)–N(2), 1.282(3); N(4)–N(5), 1.289(3);
N(7)–N(8), 1.306(3) Å. The significant elongation of the N@N bond
length implies some amount of charge delocalization, d(Cu) ? p
*
(azo) (which is supported from spectral observation, vide supra).
The pendant –CO–(CH3) forms hydrogen bonding interactions
(given in Table S3 vide Supplementary material): C(23)–
H(23B)ꢃ ꢃ ꢃO(4):H(23B)ꢃ ꢃ ꢃO(4), 2.4211 Å; C(23)ꢃ ꢃ ꢃO(4), 2.761(5) Å;
\C(23)–H(23B)ꢃ ꢃ ꢃO(4), 100.43° (symmetry: x, y, 1 + z). C(26)–
H(26B)ꢃ ꢃ ꢃO(4):H(26B)ꢃ ꢃ ꢃO(4), 2.4711 Å; C(26)ꢃ ꢃ ꢃO(4), 3.222(4) Å;
\C(26)–H(26B)ꢃ ꢃ ꢃO(4), 133.99° (symmetry: ꢀx, ꢀy, 1 ꢀ z) C(40)–
H(40A)ꢃ ꢃ ꢃO(2):H(40A)ꢃ ꢃ ꢃO(2), 2.3870 Å; C(40)ꢃ ꢃ ꢃO(2), 3.352(4) Å;
\C(40)–H(40A)ꢃ ꢃ ꢃO(2), 173.15° (symmetry: x, y, ꢀ1 + z).
3.4. Electrochemistry
The voltammogram of the complexes shows a redox response at
ꢄ0.3 V (Table 3, Fig. 4). The free ligand does not show any oxida-
tion while irreversible reductive responses appear at <ꢀ1.5 V,
which is referred to electron addition to the azo function. The
quasireversible response at 0.3 V (DEP > 100 mV) may be ascribed
to the Cu(II)/Cu(I) response [66]. On scanning at <ꢀ0.7 V potential,
an upsurge of current at av. ꢀ0.3 V is observed. The high current
density may be due to reoxidation of adsorbed Cu (metallic) on
the electrode surface which has been produced after reduction of
Cu(I) at negative potential. The peak-to-peak separation of the re-
dox couple positive to the reference electrode is dependent on the
scan rate and increases from 140 mV at 30 mV sꢀ1 to 600 mV at
1000 mV sꢀ1. At slow scan rates (30–100 mV sꢀ1),
DEP remains al-
most constant, as do the EPa and the EPc values. This corresponds to
a low heterogeneous electron-transfer rate constant which has
been influenced by the applied potential. In general, the electro-
chemical reduction of copper(II) complexes is associated with a
change in coordination geometry. The solution structure of the
copper(II) complexes show a square pyramidal or trigonal bipyra-
midal geometry, which upon reduction rearranges fast to a tetra-
hedral geometry via bond rupture and bond formation. The two
quasireversible couples at ꢀ0.8 and ꢀ1.3 V are assigned to the
N-] -
N-] - / [-N-N-]
processes [-N=N-] / [-N
tively (Table 3).
and
, respec-
[-N
Fig. 3. ORTEP plot of [Cu(L2)(SCN)]2 (2b) (H-atoms are omitted for clarity).

3152
M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
Table 3
E.p.ra and cyclic voltammetricb data.
Complexes
E.p.r data
Cyclic voltammetric datab E1/2 (V) (
DEP, mV)
g
g
A
k
CuII/CuI
CuI/Cu0
Ligand reduction
k
?
(1a)
(1b)
(2a)
(2b)
2.247
2.240
2.257
2.244
2.081
2.052
2.062
2.050
160
156
160
150
0.30 (150)
0.33 (140)
0.38 (150)
0.35 (140)
ꢀ0.30
ꢀ0.25
ꢀ0.28
ꢀ0.27
ꢀ0.78 (140)
ꢀ0.77 (140)
ꢀ0.83 (160)
ꢀ0.86 (160)
ꢀ1.25
ꢀ1.30
ꢀ1.24
ꢀ1.26
a
In MeCN solution at 77 K.
Solvent in MeCN, Pt-disk working electrode, supporting electrolyte, TBAP (0.01 M); solute concentration, 10ꢀ3 M; scan rate, 0.05 V sꢀ1
b
;
D
EP = |Epa ꢀ Epc| mV; Epa = anodic
peak potential, Epc = cathodic peak potential, V; E1/2 = 0.5(Epa + Epc) V.
pling parameter for the Cu-bridge-Cu pathway). The fit of the
magnetic data has been carried out using the formula given by
Kahn for this kind of uniform antiferromagnetic S = 1/2 chain
[23]. The best-fit parameters obtained with this model are
J = ꢀ0.5 0.1 cmꢀ1, g = 2.11 0.01 and R = 1.1 ꢂ 10ꢀ5. This result
indicates a very small antiferromagnetic coupling through the
bridging ligand. The small J value can be interpreted as a conse-
quence of the almost nil overlap between the copper(II) ions
through the ligand due to the different character (axial and equa-
torial). The symmetry of the copper(II) ion is distorted square pyra-
midal (s parameter = 0.11; 0 for sp and 1 for tbp) [93]. The major
tendency to square pyramidal avoids the necessary molecular
overlap because the electronic density in a square pyramid geom-
etry is in the dx2
orbital. No important density is in the dz2 orbital
ꢀy2
(which corresponds to the axial direction). The calculated J value
must be taken with care, because being so small, any interchain
coupling will be of the same order of magnitude.
Fig. 4. Cyclic voltammogram of [Cu(L1)Cl]n (1a) in a CH3CN–DMF (2:1, v/v) mixture
Complex 2b is a dinuclear system in which the copper atoms
are linked by two SCNꢀ bridging ligands in the axial–equatorial
form. The fit of the magnetic data has been carried out by means
using
a Pt-working electrode, Pt-auxiliary electrode and Ag/AgCl reference
electrode in the presence of ½n-But Nꢁ(ClO4) as a supporting electrolyte.
4
ˆ
of the Hamiltonian H = ꢀJS1S2, using the formula given by Kahn
3.5. EPR spectra
for this kind of complex [23]. The best-fit parameters obtained
with this model are J = ꢀ25.8 0.5 cmꢀ1
, g = 2.06 0.01 and
R = 2.3 ꢂ 10ꢀ5. The medium J value can be interpreted as a conse-
quence of the noticeable overlap between the copper(II) ions
through the ligand due to the different character, axial and equato-
The EPR spectra (Fig. 5; Table 3) of powdered samples recorded
at room temperature (298 K) are identical to those at liquid N2
temperature (77 K). The frozen solution spectra show better signal
resolution. The EPR spectra of the Cu(II) complexes show four line
rial (with the
ter = 0 for sp and 1 for tbp [93]). The electronic density is
intermediate between the dz2 and dx2 orbitals, allowing a consid-
s Addison parameter = 0.5, 0.45 and 0.17; s parame-
(
63Cu, I = 3/2) EPR spectra. The three peaks of low intensity in the
weaker field are considered to originate from the gk component,
and A|| lies at 140–150 ꢂ 10ꢀ4 cmꢀ1. The calculated gk and gperp val-
ues for these complexes were 2.2 and 2.01, respectively. The rela-
tion gk > g? > 2.0023 agrees with a ground state configuration of
ꢀy2
erable overlap between them through the SCNꢀ bridging ligands.
The magnetic result supports a stronger antiferromagnetic ex-
change in the –SCN-bridging compound 2b than the –Cl-bridging
1a. A Mulliken spin density calculation using the optimized geom-
etries of the complexes indirectly supports a higher antiferromag-
netic coupling in –SCN-bridged 2b than Cl-bridged 1a.
dx2
.
ꢀy2
3.6. Magnetic properties
The magnetic properties of the complexes [Cu(L1)Cl]n (1a) and
3.7. Correlation with electronic structure, spectra, magnetism and
redox properties
[Cu(L2)(NCS)]2 (2b) are shown in Fig. 6 as
vMT vs T and M/NlB vs H
(inset), respectively. The value of
v K
MT at 300 K is 0.42 cm3 molꢀ1
for 1a and 0.80 cm3 molꢀ1 K for 2b, which are as expected for mag-
netically quasi-isolated spin doublets (g > 2.00). Starting from the
The molecular structures of 1a and 2b are optimized by using
B3LYP/DFT calculations of the G03 program. The computed struc-
tures well reproduce the experimental structures for 1a and 2b
(Supplementary Tables S1–S3). The theoretical bond distances
are longer in the optimized structures for Cu–O (average 0.07 Å)
and Cu–S (0.04 Å for 1a and average 0.14 Å for 2b) whilst the
Cu–N (av. 0.02 Å) distances are shorter than those of the X-ray
determined structures. Features of some selected occupied and
unoccupied frontier orbitals are shown in Fig. 7. Energy level cor-
relations along with the qualitative composition of the molecular
orbitals of the Cu(O, N, S) unit are given in Supplementary Fig. S1
(vide Supplementary material). The unpaired electron of Cu(II) in
1a resides in a SOMO (singly occupied MO) (ꢀ3.6 eV). In the di-
meric structure of 2b, two unpaired electrons occupy SOMO1 and
room temperature, the
vMT values are practically constant up to
50 K, and below 50 K they decreases quickly to 0.34 cm3 molꢀ1
K
at 2 K. This global feature is characteristic of very weak, almost nil,
antiferromagnetic interactions. The reduced molar magnetizations
at 2 K (Fig. 6 inset) clearly indicate that the antiferromagnetic cou-
pling, if any, is very small. The M/N
tron and the curve follows the Brillouin law, assuming g = 2.10 for
1a and close to 0.03 N B in 2b (very far from the value of 2 N B ex-
pected if the antiferromagnetic coupling was weak).
lB value at 5 T is close to 1 elec-
l
l
Complex 1a is actually a one-dimensional system in which the
copper atoms are linked by Cl-bridging ligands in an axial–equato-
rial form. This feature gives a uniform S = 1/2 system (with a J cou-

M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
3153
Fig. 5. EPR spectrum of [Cu(L1)(SCN)]2 (2a).
a
0.42
0.40
0.38
0.36
0.34
1.0
0.8
0.6
0.4
0.2
0.0
μ
N
M
Cu, 0.426;
thio, 0.157; Oenolate, 0.098; N=Nazo,
T
m
χ
S
0
10000 20000 30000 40000 50000
H / G
0.154; Cl, 0.155e
0
50
100 150 200 250 300
T / K
b
0.8
0.6
0.4
0.2
0.0
0.03
0.02
0.01
0.00
μ
N
M
T
m
χ
Cu, 1.074; Sthio
, 0.223; Oenolate,
0
10000 20000 30000 40000 50000
H / G
0.155; N=Nazo, 0.284e
0
50
100 150 200 250 300
T / K
Fig. 6. Plot of the susceptibility data, v
MT vs T for (a) [Cu(L1)Cl]n (1a) and (b) [Cu(L2)(NCS)]2 (2b) assuming a dinuclear entity. Inset: plot of the reduced magnetization, M/NlB
vs H data at 2 K. Mulliken spin densities to some atoms are given.
SOMO2. These functions are non-degenerate. The LUMOs are con-
stituted by >95% ligand contribution (vide Supplementary Table
S4). Mulliken spin densities around Cu(O, N, S, Cl) are Cu, 0.426;
The electronic absorption spectra are measured at room tem-
perature in chloroform, and the experimental absorption bands
are assigned using the time-dependent DFT method. The experi-
mental absorption spectra of the complexes are shown in Fig. 1.
The calculated wavelengths and their assignment are given in
Sthio, 0.157; Oenolate, 0.098; N@Nazo, 0.154; Cl, 0.155e for (1a), and
Cu, 1.074; Sthio, 0.223; Oenolate, 0.155; N@Nazo, 0.284e for 2b (Fig. 6).

3154
M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
E = -2.73 eV, 01 %
E = -6.46 eV, 02 % (Cu),
E = -1.41 eV, 04 %
(Cu), 96% (L)
E = -3.6 eV, 46 % (Cu),
41% (L), 13% (Cl)
SOMO(74)
(Cu), 99% (L)
88% (L), 10% (Cl)
HOMO-1(73)
LUMO(75)
LUMO+1(76)
[Cu(L1)Cl]n (1a)
E = -3.45 eV, 53 %
(Cu), 39% (L), 08%
(NCS)
E = -3.57 eV, 54 % (Cu),
38% (L), 07% (NCS)
E = -2.33 eV, 01 %
(Cu), 99% (L)
E = -2.38 eV, 01 %
(Cu), 99% (L)
SOMO1 (168)
SOMO2 (167)
LUMO (169)
LUMO+1 (170)
[Cu(L2)(SCN)]2 (2b)
Fig. 7. Contour plots of some selected MOs of [Cu(L1)Cl]n (1a) and [Cu2(L2)2(SCN)2] (2b).
Table 4. There are two transitions in the spectra of the Cu(II) com-
plexes in the visible region (400–625 nm) (vide Section 2). TD-DFT
computation of the optimized geometry of 1a gives a weak transi-
tion at 591 nm (f, 0.0054), which is a mixture of d–d and MLCT
bands, and in the experimental spectrum this band appears at
608 nm. The calculated transitions at 579.4, 424.4 and 416.7 nm
be assigned to the mixture of XMCT and LMCT transitions. A calcu-
lated intense band at 382.7 nm (f, 0.321) is assigned to the
*
L(p) ? L(p ) transition and in the experimental spectrum it is ob-
served at <300 nm. The calculated transitions for [Cu(L2)(SCN)]2
(2b), 400–700 nm, are dominated by LMCT transitions along with
a minor contribution from XMCT transitions. The transitions
*
<350 nm are mainly ascribed to ligand centred p ? p transitions.
are the admixture of XMCT (Cl(pp) ? Cu(dp)) and LMCT
(L( ) ? Cu(d ), RS( ) ? Cu(d )). In the experimental spectrum
p
p
p
p
Cyclic voltammetric behaviour of the complexes may be ex-
we observed an intense band at 405 nm (e, 10 418) which may
plained from the DFT calculation. Because of the higher metal
Table 4
Electronic transitions obtained from TD-DFT/UB3LYP computations of 1a and 2b.
Energy (eV)
Wavelength (nm)
Osc. strength
Key transitions
Character
Cu(L1)Cl]n (1a)
2.0966
591.3
579.4
424.4
0.0054
0.0337
0.0171
(59%)74(
a
) ? 75(
a
)
Cu(d
Cu(d
p
) ? L(
p
*)
(39%)73(b) ? 75(b)
(42%)70(b) ? 74(b)
(21%)72(b) ? 74(b)
(38%)71(b) ? 74(b)
(22%)69(b) ? 74(b)
(57%)69(b) ? 74(b)
(27%)73(b) ? 75(b)
p) ? Cu(dp)
2.1397
2.9213
Cl(p
L( ) ? Cu(d
Cl(p ) ? Cu(d
p
) ? Cu(d
p
)
)
p
p)
p
p
L(p
L(p
L(p
)/Cl(p
)/Cl(p
) ? L(p
*)
p) ? Cu(d
p
p
)
)
2.9752
3.2397
416.7
382.7
0.0354
0.2113
p) ? Cu(d
(23%)73(a) ? 75(a)
[Cu(L2)(SCN)]2 (2b)
1.5685
1.8479
790.4
670.9
0.0263
0.0141
(54%)164(b) ? 167(b)
(38%)162(b) ? 167(b)
(27%)162(b) ? 168(b)
(36%)161(b) ? 167(b)
(18%)161(b) ? 168(b)
(33%)160(b) ? 167(b)
(22%)160(b) ? 168(b)
(27%)150(b) ? 168(b)
(26%)161(b) ? 168(b)
(30%)160(b) ? 168(b)
(27%)159(b) ? 168(b)
(68%)166(b) ? 169(b)
SCN(p)/L(p) ? Cu(dp)
L(p
L(p
L(p
) ? Cu(d
) ? Cu(d
) ? Cu(d
p)
p)
p)
2.1047
2.1672
2.7805
2.9323
3.0429
589.1
572.1
445.9
422.8
407.4
0.0267
0.0233
0.0138
0.0549
0.0886
L(p
) ? Cu(d
p)
L(p
L(p
L(p
)/Cu(d
) ? Cu(d
)/SCN( ) ? Cu(dp)
p) ? Cu(dp)
p)
p
SCN(p) ? L(p
*)

M.K. Paira et al. / Polyhedron 29 (2010) 3147–3156
3155
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(Cu) function in the SOMO/HOMO-1, the observed oxidation is cor-
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are significantly dominated by the ligand function (>95%), thus
reduction may refer to electron accommodation at the azo domi-
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is justified.
The spin density calculation has explained the degree of delo-
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bridged Cu–X–Cu unit. The coordinating atoms of the ligand partic-
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to the enhancement of the electron density of the donor atoms.
Interestingly, the spin density is mainly distributed amongst the
copper dx2
magnetic orbital and the Cl/NCS bridging between
ꢀy2
two Cu centres (Cu(1)ꢃ ꢃ ꢃCu(2)) in the dinuclear entity. It is to be
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Acknowledgements
Financial support from the CAS program, University Grants
Commission and Department of Science & Technology, New Delhi
are gratefully acknowledged. One of us, MP, thanks CSIR for a fel-
lowship. J.R. acknowledges the financial support from the Spanish
Government (Grant CTQ2006/03949).
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Appendix A. Supplementary material
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CCDC 753060 and 753061 contain the supplementary crystallo-
graphic data for [Cu(L1)Cl]n (1a) and [Cu(L1)Cl]n (1a). These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.poly.2010.08.024.
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