Electronic structure of thioether containing NSNO donor azo-ligand and its copper(II) complex: Experimental and theoretical studies

Article abstract of DOI:10.1016/j.molstruc.2015.06.048

Synthesis of thioether containing NSNO donor azo ligand (HL) showing hydrazoketo and azoenol tautomerism has been performed. The hydrazoketo and azoenol equilibrium of HL has been studied. The hydrazoketo form of HL is predominating over azoenol form. In

Full text of DOI:10.1016/j.molstruc.2015.06.048

Journal of Molecular Structure 1099 (2015) 92e98
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Electronic structure of thioether containing NSNO donor azo-ligand
and its copper(II) complex: Experimental and theoretical studies
Ajoy Kumar Pramanik, Deblina Sarkar, Tapan Kumar Mondal*
Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis of thioether containing NSNO donor azo ligand (HL) showing hydrazoketo and azoenol
tautomerism has been performed. The hydrazoketo and azoenol equilibrium of HL has been studied. The
hydrazoketo form of HL is predominating over azoenol form. In copper(II) complex the ligand is present
in azoenol form. The electronic spectra and electronic structure of the complex has been extensively
studied. The structures of the ligand and copper(II) complex have been established from single crystal X-
Received 21 March 2015
Received in revised form
8 June 2015
Accepted 13 June 2015
Available online 19 June 2015
ray studies. The 1-D supramolecular structure of the complex is formed by pep interactions.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Hydrazoketo and azoenol tautomerism
NSNO donor azo ligand
Xeray and electronic structure
DFT and TDDFT calculations
1. Introduction
system of
p-conjugated double bonds; this system has been
referred to as RAHB (resonance-assisted hydrogen bonding). It has
Azo compounds are a very important class of chemical com-
pounds receiving attention in scientific research for the last few
decades. They are highly colored and have been used as dyes and
pigments for a long time [1,2]. Furthermore, they have been studied
widely because of their excellent thermal and optical properties in
applications such as optical recording medium [3], toner [4,5] and
ink-jet printing [6,7]. Recently, azo metal chelates have also
attracted increasing attention due to their interesting electronic
and geometrical features in connection with their application for
molecular memory storage, nonlinear optical elements, and print-
ing systems [8].
been used successfully to explain intra- and inter-molecular OeH
… O hydrogen bonds in compounds containing the b-diketo enol
fragment [13e16] and to explain NeH … O bonds in molecules
containing the HNeN]CeC]O fragment [17e19]. The X-ray
structure of [H2L](ClO4) reveals the existence of hydrazoketo form
in the solid state which is further supported by spectral studies.
When HL binds with Cu2þ the equilibrium is shifted from hydra-
zoketo to azoenol form and is supported by the X-ray structure of
[Cu(L) (H2O)](ClO4). The hydrazoketo to azoenol tautomerism of HL
and the electronic structure of Cu(II) complex have been inter-
preted by DFT studies.
In this work we have synthesized thioether containing NSNO
donor azo ligand (HL) showing hydrazoketo and azoenol tautom-
erism (Scheme 1). The equilibrium between the hydrazoketo and
azoenol forms of organic molecules, containing the HNeN]CeC]
O group, is well known. This process has been studied because of
their importance in the dyestuff industry and as acidebase in-
dicators [9]. The organic compounds containing this group show
strong intramolecular hydrogen bonding between the NeH and CO
fragments [10e12]. Strong hydrogen bonds occur due to the fact
that the neutral donor and acceptor atoms are connected by a
2. Experimental
2.1. Materials
All the reagents and solvents were purchased from commercial
sources and used as received. 2-Aminothiophenol and 2-(chlor-
omethyl)pyridine hydrochloride was purchased from Sigma
Aldrich. 2-((Pyridine-2-yl)methylthio)benzenamine was prepared
following the published procedure [20]. Acetyl acetone (acac) and
inorganic metal salts were made available from E. Merck, India. All
other organic chemicals and inorganic salts used were of A.R.
quality and were available from Sisco Research Lab, Mumbai, India
and did not require further purification. The solutions spectral
* Corresponding author.
E-mail address: tkmondal@chemistry.jdvu.ac.in (T.K. Mondal).
http://dx.doi.org/10.1016/j.molstruc.2015.06.048
0022-2860/© 2015 Elsevier B.V. All rights reserved.

A.K. Pramanik et al. / Journal of Molecular Structure 1099 (2015) 92e98
93
[MH]þ.
2.2.2. Synthesis of copper(II) complex
To an absolute ethanolic solution (15 ml) of HL (0.327 g,
1.0 mmol), 10 ml ethanolic solution of hydrated metal salt of
Cu(ClO4)2.6H2O (0.371 g, 1.0 mmol) was added dropwise under
magnetically stirring condition. The stirring was continued gently
for six hours. The resultant orange yellow solution changed to dark
green during the course of reaction. The reaction mixture was
filtered and the resultant solution was kept undisturbed for slow
evaporation of the solvent in air. Upon subsequent concentration
over a week, two types of crystals were deposited on the wall of
beaker. The dark green crystals of complex was separated first,
washed with ethanol and hexane and dried over CaCl2. Then a deep
yellow crystalline compound of ligand suitable for single crystal X-
ray study was found.
Scheme 1. Hydrazoketo and azoenol equilibrium of HL.
studies were carried out using spectroscopic grade solvents from
Lancaster, U.K. Commercially available SRL silica gel (60e120 mesh)
was used for column chromatography.
Caution! Perchlorate salts of transition metal complexes con-
taining organic ligands are potentially explosive [21]! Only small
quantities of material should be prepared, and they should be
handled with great caution.
[Cu(L) (H2O)](ClO4): Deep green crystalline compound. Yield:
0.237 g (54%); Anal. Calc. for C17H18N3O7SCuCl: C, 40.24; H, 3.58; N,
8.28. Found: C, 40.27; H, 3.81; N, 8.92%. IR data (KBr disc) (cmꢀ1):
3450-3436 y(OeH), 1667 n(C]O), 1417 y(N]N), 1082, 1117 y
(ClOꢀ4 ).
2.2. Physical measurements
lMax (ε, Me1 cmꢀ1) in acetonitrile: 589(452), 527(447), 416(13917),
381(sh), 290(13485), 263(18169). ESI‒MS, m/z: 508 [MH]þ.
Melting Point of the ligand was determined using a digital
melting point apparatus. Microanalyses (C, H, N) were performed
using a PerkineElmer SerieseII CHN-2400 CHNS/O elemental
analyzer. The electronic spectra were measured on Lambda 750
Perkin Elmer spectrophotometer in acetonitrile solution. The IR
spectra were recorded on RXe1 Perkin Elmer spectrometer in the
spectral range 4000e400 cme1 with the samples in the form of KBr
pellets. 1H NMR spectrum of HL was recorded in CDCl3 on Bruker
(AC) 300 MHz FTeNMR spectrometer in presence of TMS as inter-
nal standard. ESI mass spectra were recorded on a micro mass Q‒
TOF mass spectrometer. Molar conductance was measured using
Systronics conductivity meter (Model 304) using 10ꢀ3 M solution in
acetonitrile.
L
M
¼ 117 Uꢀ1 molꢀ1 cm2 in acetonitrile.
2.3. Crystal structure determination and refinement
Crystals suitable for X-ray diffraction study of [H2L](ClO4) and
[Cu(L) (H2O)](ClO4) were grown by slow evaporation of the solvent
in air kept undisturbed at room temperature and at ambient con-
dition for
a week. Complex [Cu(L) (H2O)](ClO4) crystallizes
contemporarily with HL as [H2L](ClO4). Details of crystal analyses,
data collection and structure refinement data are given in Table 1.
The X-ray data were collected on a Bruker AXS Kappa smart Apex-II
diffractometer equipped with an Apex-II CCD area detector using a
fine focus sealed tube as the radiation source of graphite mono-
chromator Mo K
were determined from least-squares refinement method. Reflec-
tion data were recorded using the scan technique. Data were
corrected for Lorentz polarization effects and for linear decay. Semi-
empirical absorption corrections based on -scans were applied.
a
radiation (
l
¼ 0.71073 Å). Unit cell parameters
2.2.1. Synthesis of ligand (HL)
2-((Pyridine-2-yl)methylthio)benzenamine (1.729 g, 8.0 mmol)
was dissolved in 10 ml 12(N) HCl. Then it was cooled in ice and an
ice cold NaNO2 (0.552 g, 8.0 mmol) solution was added to this ice
cold amine solution dropwise at 0e5 ꢁC under stirring condition
and the resulting solution was kept in an ice-bath. Separately, an ice
cold solution of acetylacetone (0.801 g, 8 mmol) was prepared in
5(N) Na2CO3 (6.36 g in 50 ml water) solution. The diazotized so-
lution was then slowly added to the cold alkaline solution with
vigorous stirring. Stirring was continued for 30 min after the
addition was complete. The whole mixture was then kept under
refrigeration for 1 h. Yellow precipitate of HL was obtained. The
crude product was collected by filtration, washed thoroughly with
water and dissolved in minimum volume of 1(N) HCl and then
Na2CO3 solution was added to it for reprecipitation of the com-
pound. It was then filtered again and washed with distilled water.
Finally dried over CaCl2. The dry mass was dissolved in minimum
volume of CH2Cl2 and was purified by column chromatographic
separation on silica gel. An orange-yellow band was eluted with EA-
PE (1:3, v/v).
u
j
The structure was solved and refined by full-matrix least-squares
techniques on F2 using WinGX [22] and the SHELXL-97 [23] pro-
gram. The absorption corrections were done by the multi-scan
technique. The data were reduced and integrated using the SAINT
[24] program. A Semi-empirical multi-scan absorption correction
was made with SADABS [25]. All data were corrected for Lorentz
and polarization effects, and the non-hydrogen atoms were refined
anisotropically with SHELXS-97 [23]. Hydrogen atoms were
generated in the refinement process as per the riding model with
thermal parameters equal to 1.2 times that of associated C atoms,
and participated in the calculation of the final R-indices. All cal-
culations were carried out using SHELXS 97 [23]. Figures of the
structure were drawn with ORTEP-32 [26] programs with 35%
ellipsoidal probability.
2.4. Computational details
[HL]: Orange-yellow solid, Yield was 1.758 g, (62%); Decompo-
sition temperature ~ 67 ꢁC. Anal. Calc. for C17H17N3O2S: C, 62.36; H,
5.23; N, 12.83. Found (%): C, 62.57; H, 5.27; N, 12.91%. IR data (KBr
All computations were performed using the Gaussian09 (G09)
program [27]. Full geometry optimizations of ligand and copper
complex were carried out using the density functional theory
method at the RB3LYP and UB3LYP level of theory [28,29]. The 6-
31G(d) basis set for C, H, N, O and S atoms was used. The LanL2DZ
basis set with effective core potential was employed for the copper
atom [30e32]. The vibrational frequency calculations were per-
formed to ensure that the optimized geometries represent the local
disc) (cmꢀ1): 3430
N), 1505 (C]C), 1438
y
(NeH), 2926
y
(CeH), 1673
y
(C]O), 1577
n(C]
n
y
(N]N). 1H NMR data in CDCl3
(d
, ppm):
14.97 (s, 1H), 8.43 (d, J ¼ 5.2 Hz, 1H), 7.74 (d, J ¼ 8.2 Hz, 1H), 7.52 (d,
J ¼ 8.5 Hz, 1H), 7.36e7.39 (m, 2H), 7.47 (d, J ¼ 7.8 Hz, 1H), 7.06e7.10
(m, 2H), 4.11 (s, 3H), 2.62 (s, 3H), 2.48 (s, 3H). lMax (ε, Mꢀ1 cmꢀ1) in
acetonitrile: 403 (sh), 368 (21086), 255 (17210). ESI‒MS, m/z: 328

94
A.K. Pramanik et al. / Journal of Molecular Structure 1099 (2015) 92e98
Table 1
Summarized crystallographic data and refinement parameters for [H2L](ClO4) and [Cu(L) (H2O)](ClO4).
Formula
C17H18ClN3O6S
C17H18ClCuN3O7S
Formula weight
Crystal color
Crystal system
Space group
a, b, c [Å]
427.85
Orange yellow
Triclinic
P-1
507.39
Green
Monoclinic
P21/c
10.6998(4) 13.3428(6)
14.8222(6)
90.00
106.302(2)
2031.02(14)
4
5.043(5), 8.234(5), 24.362(5)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
81.297(5)
86.093(5)
82.150(5)
989.4(12)
2
1.436
0.338
444
V [ Å3]
Z
D(calc) [g/cm3]
Mu(Mo-Ka)/mmꢀ1
F(000)
1.659
1.356
1036
Crystal size [mm3]
Data collection
Absorption correction
Temperature (K)
Radiation [Å]
0.22 ꢂ 0.18 ꢂ 0.15
0.23 ꢂ 0.17 ꢂ 0.15
Multi-scan
293(2)
0.71073
Multi-scan
293(2)
0.71073
q
(Min-Max) [0]
1.69e25.00
ꢀ5 to 5, -9 to 9, -28 to 28
13955, 3449, 0.0537
2840
1.98e25.50
Dataset (h; k; l)
Total, unique data, R(int)
Observed data [I > 2
Refinement
Nref, Npar
R, wR2
D
Goodness of fit(S)
ꢀ12 to 12; ꢀ14 to16; ꢀ17 to 17
14905, 3727,0.0434
2944
s(I)]
3371, 301
0.0655, 0.1337
0.930, 0.951
1.016
3727, 273
0.0860,0.0687
1.689, 1.740
0.994
q(max)and
D
q(min) (e/Å3)
minima of potential energy surface and there are only positive
Eigenevalues. The lowest 40 singletesinglet vertical electronic
excitations based on B3LYP optimized geometries were computed
using the time-dependent density functional theory (TD-DFT)
formalism [33e35] in acetonitrile using conductor-like polarizable
continuum model (CPCM) [36e38] using the same B3LYP level and
basis sets. GaussSum [39] was used to calculate the fractional
contributions of various groups to each molecular orbital.
3. Results and discussion
3.1. Synthesis and formulation
A thioether containing tetradentate monobasic NSNO donor
ligand (HL) has been synthesized with high yield and in a desirable
reaction time (Scheme 2). The ligand is characterized by several
spectroscopic techniques and elemental analysis. The 1H NMR
signals taken in CDCl3 well supported the proposed structure of the
ligand. The S-methylene protons appear at 4.11 ppm as sharp
singlet, eCH3 protons of acetylacetone part appear as sharp singlets
at 2.42 and 2.61 ppm. The well resolved aromatic protons appear at
7.06e8.43 ppm. The characteristic hydrogen bonded broad singlet
peak corresponds to OeH or NeH appears at 14.97 ppm. IR spec-
Scheme 2. Synthetic route of HL.
trum of ligand shows characteristic
N) at 3430 and 1438 cmꢀ1 respectively. The
appears at 1673 cmꢀ1
y
(XeH) (X ¼ O or N), and
y(N]
(C]O) of the ligand
y
.
The ligand may exist either in hydrazoketo or in azoenol form or
may be in equilibrium (Scheme 3). To study the hydrazoketo and
azoenol equilibrium of HL, potential energy scan has been carried
out (Fig. 1). The energy scan shows that the hydrazoketo form is
more stable by 10.19 kcal/mol compared to the azoenol form of the
ligand which supports the experimental results as well. The exis-
tence of hydrazoketo form is again supported from the single X-ray
crystal structure of HL.
In presence of Cu2þ in solution the equilibrium is shifted to-
wards azoenol form and the ligand gets coordinated to copper(II) in
azoenol form which is well supported by spectral studies and
Scheme 3. Azoenol and hydrazoketo equilibrium of HL.

A.K. Pramanik et al. / Journal of Molecular Structure 1099 (2015) 92e98
95
Fig. 3. ORTEP plot of [Cu(L) (H2O)]þ with 35% ellipsoidal probability.
Table 2
Some selected bond distances (Å) and angles (ꢁ) of [H2L](ClO4).
Bonds(Å)
X-ray
Angles (ꢁ)
X-ray
Fig. 1. Potential energy scan with the variation of NeH bond distance by DFT/B3LYP/6-
31G(d) method.
N(2)-N(3)
S(1)-C(6)
1.315(4)
1.828(4)
1.307(4)
1.219(5)
1.209(5)
1.478(5)
1.307(4)
C(6)-S(1)-C(7)
101.8(2)
120.1(3)
119.3(3)
119.4(3)
121.0(3)
123.9(3)
113.1(3)
121.3(3)
C(12)-N(2)-N(3)
O(1)-C(14)-C(13)
O(1)-C(14)-C(15)
N(2)-N(3)-C(13)
N(3)-C(13)-C(14)
N(3)-C(13)-C(16)
C(13)-C(16)-O(2)
O(2)- C(16)-C(17)
C(13)-C(16)-C(17)
C(13)-C(14)-C(15)
N(3)-C(13)
O(1)-C(14)
O(2)-C(16)
C(13)-C(14)
N(3)-C(13)
120.5 (4)
118.1(3)
121.2(3)
interaction in the molecule [40]. To know the electrolytic nature of
the complex in solution, conductivity measurement has been car-
ried out. The molar conductance (L ) of complex in CH3CN is
M
Scheme 4. Synthesis of copper(II) complex with HL.
126
U
ꢀ1cm2 molꢀ1. Thus, the complex is 1:1 electrolyte in
acetonitrile.
confirmed by single crystal X-ray structure of [Cu(L) (H2O)](ClO4).
The synthesis of copper(II) complex is shown in Scheme 4. The IR
y , y
(N]N) at 1417 cmꢀ1 (ClO4ꢀ) at
3.2. X-ray structure
spectrum of the complex shows
1082 and 1117 cmꢀ1 which well supports the complex formation
and the splitting of
(ClOꢀ4 ) stretching indicates the H-bonded
The ligand HL and the copper(II) complex crystallize from
y
Table 3
Selected bond distances (Å) and bond angles (ꢁ) of [Cu(L) (H2O)](ClO4).
Bonds(Å)
X-ray
DFT/B3LYP
Cu(1)-N(1)
Cu(1)-N(2)
Cu(1)-O(1)
Cu(1)-O(3)
Cu(1)-S(1)
N(2)-N(3)
N(3)-C(13)
C(13)-C(16)
1.990(5)
1.914(5)
1.915(4)
2.296(5)
2.2730(14)
1.296(6)
1.349(7)
1.486(8)
1.258(6)
1.212(7)
2.096
1.977
1.947
2.282
2.392
1.281
1.335
1.453
1.265
1.220
O(1)-C(14)
O(2)-C(16)
Angles (ꢁ)
N(1)-Cu(1)-N(2)
N(2)-Cu(1)-O(1)
N(1)-Cu(1)-O(3)
N(1)-Cu(1)-S(1)
N(1)-Cu(1)-O(1)
N(2)-Cu(1)-O(3)
N(2)-Cu(1)-S(1)
O(1)-Cu(1)-O(3)
O(1)-Cu(1)-S(1)
O(3)-Cu(1)-S(1)
149.59(19)
91.48(18)
104.40(19)
85.36(13)
94.88(18)
105.73(19)
88.44(13)
85.5(2)
143.34
90.84
97.98
83.62
97.92
118.09
86.84
86.62
177.61
94.98
179.66(15)
94.21(15)
Fig. 2. ORTEP plot of [H2L](ClO4) with 35% ellipsoidal probablity.

96
A.K. Pramanik et al. / Journal of Molecular Structure 1099 (2015) 92e98
Fig. 4. 1D supramolecular network involving
p/p .
interaction along c-axis for [Cu(L) (H2O)]þ
Fig. 8. Spin density plot of [Cu(L) (H2O)]þ
.
Fig. 5. Optimized structure of [Cu(L) (H2O)]þ by DFT/B3LYP method.
methanolewater mixture. The complex crystallizes with aqua
ligand in the metal coordination sphere. Complex [Cu(L)
(H2O)](ClO4) crystallizes contemporarily with HL as [H2L](ClO4).
The ORTEP plots of HL and its copper complex are shown in Figs. 2
and 3 respectively. The bond parameters for [H2L](ClO4) supports
the hydrazoketo form. The O(1)-C(14) and O(2)-C(16) bond dis-
tances are 1.219(5) and 1.209(5) Å which perfectly match with the
C]O bond distances. The hydrazoketo form of the ligand are sup-
ported by the shorter N(3)-C(13) (1.307(4) Å) and longer C(13)-
C(14) (1.478(5) Å) bond distances (Table 2). The longer N(2)-N(3),
1.315(4) Å also confirms the existence of hydrazoketo form of the
ligand. In [Cu(L) (H2O)](ClO4), copper is penta-coordinated having
the geometry intermediate between distorted square pyramid and
trigonal bipyramid. The trigonality index [41]
)/60 where and are the main opposed angles in the coordi-
nation polyhedron and for perfect square pyramidal and trigonal
t
value is 0.50 [
t
¼ (b-
a
a
b
bipyramidal geometries the values of
t are zero and unity respec-
tively. In the present case
b
¼ O(1)eCu(1)eS(1) ¼ 179.66(15)ꢁ and
a
¼ N(1)eCu(1)eN(2) ¼ 149.59(19)ꢁ] (Table 3). According to the
Fig. 6. Contour plots of selected molecular orbitals (a .
-spin) of [Cu(L) (H2O)]þ
Table 4
Energy and composition of selected molecular orbitals (
a
-spin) of [Cu(L) (H2O)]þ.
MOs
Energy (eV)
% of composition
Cu
L
LUMOþ5
LUMOþ4
LUMOþ3
LUMOþ2
LUMOþ1
LUMO
ꢀ3.16
ꢀ3.52
55
03
05
01
02
01
02
02
10
0
05
03
10
13
03
37
01
45
97
95
99
98
99
98
98
90
100
95
97
90
87
97
63
99
ꢀ3.88
ꢀ4.10
ꢀ4.71
ꢀ5.38
HOMO
ꢀ9.03
HOMO-1
HOMO-2
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO-8
HOMO-9
HOMO-10
ꢀ9.09
ꢀ9.57
ꢀ10.16
ꢀ10.67
ꢀ10.72
ꢀ10.93
ꢀ11.35
ꢀ11.65
ꢀ11.71
ꢀ12.15
Fig. 7. Contour plots of selected molecular orbitals (b .
-spin) of [Cu(L) (H2O)]þ

A.K. Pramanik et al. / Journal of Molecular Structure 1099 (2015) 92e98
97
Table 5
there is a series of essentially parallel units whose relative dispo-
sition is ideal for aromatic stacking interactions, forming a
1D supramolecular continuum. The dimmer repeats along c-axis
and they are under face-to-face interaction of pyridyl and
aminothiophenyl ring to form the -stack, with centroidecentroid
Energy and composition of selected molecular orbitals (b
-spin) of [Cu(L) (H2O)]þ.
p
… p
MOs
Energy (eV)
% of composition
Cu
p
… p
p
L
LUMOþ5
LUMOþ4
LUMOþ3
LUMOþ2
LUMOþ1
LUMO
ꢀ3.52
ꢀ3.87
03
05
01
02
01
47
03
02
0
16
02
05
12
36
27
29
30
97
95
99
98
99
53
97
98
100
84
98
95
88
64
73
71
70
distance of 3.549 (4) Å for [Cg(4) … Cg(5)] (symmetry: x, 3/2-y, 1/
2 þ z) and 3.548 (4) Å [Cg(5) … Cg(4)] (symmetry: x, 3/2-y, ꢀ1/
ꢀ4.09
2
þ
z) (where, Cg(4)
¼
N1,C1,C2,C3,C4 and C5 and
ꢀ4.69
ꢀ5.33
Cg(5) ¼ C7,C8,C9,C10,C11 and C12).
ꢀ6.71
HOMO
ꢀ8.99
3.3. DFT computation and electronic structure of [Cu(L) (H2O)]þ
HOMO-1
HOMO-2
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO-8
HOMO-9
HOMO-10
ꢀ9.15
ꢀ10.14
ꢀ10.19
ꢀ10.68
ꢀ10.74
ꢀ11.01
ꢀ11.37
ꢀ11.52
ꢀ11.75
ꢀ12.09
To understand the electronic structure of the complex DFT
calculation has been performed on [Cu(L) (H2O)]þ. The full geom-
etry optimization for the compound has been carried out in the
DFT/UB3LYP level. Some selected optimized bond parameters are
given in Table 3. The optimized bond lengths and bond angles well
reproduced the Xeray data of the complex. Optimized structure of
[Cu(L) (H2O)]þ is shown in Fig. 5. Contour plots of some selected
molecular orbitals of a-spin and b-spin are shown in Figs. 6 and 7
respectively. Fig. 8 represents the spin density of the unpaired
spin distributed over the coordinated atom along with major
contribution on copper center. Energy and compositions of some
selected molecular orbitals
and 5 respectively.
a-spin and b-spin are given in Tables 4
3.4. TDDFT calculation and electronic transitions of [Cu(L) (H2O)]þ
The experimental electronic spectra of the compounds in
acetonitrile are shown in Fig. 9. In 200e900 nm range the complex
exhibits two very low intense peaks at 589 and 547 nm. Moderately
intense sharp bands at 416 nm and 263 nm have been observed
along with shoulders at 290 and 381 nm. To simulate the experi-
mental electronic spectra of the complexes TDDFTcalculations have
been performed in acetonitrile. The weak bands at 589 and 547 nm
correspond to ded transitions in the complex (Table 6). The strong
peak at 416 nm has
transition, ILCT) character. In addition, the broad peaks at 290 and
381 nm have mixed LMCT and ILCT character.
p(L) / p
*(L) (intra-ligand charge transfer
Fig. 9. UVeVis spectra of HL (e) and [Cu(L) (H2O)](ClO4) (
shows the expanded spectrum for the complex).
) in acetonitrile (inset
values, the coordination geometry around copper ion is interme-
diate between trigonal bipyramidal and square pyramidal geome-
tries and is better described as distorted square based pyramidal
(DSBP) [42e44] with one water molecule occupying the axial po-
sition. In the complex copper atom is displaced by 0.248 Å above
the N2SO coordination plane and towards the elongated apical
oxygen atom [45].
The presence of aqua ligand in the metal coordination sphere
leads to the formation of H-bonding interaction, between the co-
ordinated water molecules and the counter perchlorate anions,
which connects the complexes about a center of symmetry. Packing
4. Conclusion
We have successfully synthesized thioether containing NSNO
donor azo ligand (HL) showing hydrazoketo and azoenol tautom-
erism. The equilibrium between the hydrazoketo and azoenol
forms of the ligand has been theoretically established. In the un-
coordinated state the hydrazoketo form is predominating over
azoenol form. In copper(II) complex the ligand is present as azoenol
state. The electronic spectra and electronic structure of the complex
has been extensively studied. The structures of the ligand and
copper(II) complex have been established from single crystal X-ray
studies. The complex forms 1-D supramolecular structure by H-
diagram of the complex shows
p … p interactions between aro-
matic rings to from 1D supramolecular network (Fig. 4). Hence,
bonding interactions and
pe
p
stacking of the aromatic rings.
Table 6
Vertical electronic transitions of [Cu(L) (H2O)]þ calculated by TDDFT/CPCM method.
Excitation energy (eV)
Wavelength (nm)
Osc. strength (f)
Transition
Character
2.0155
2.2646
3.0626
3.1621
3.2061
3.7143
4.1254
615.2
547.5
404.8
392.1
386.7
333.8
300.5
0.0184
0.0147
0.0370
0.0587
0.0945
0.4570
0.0378
(55%)HOMO-8(
(49%)HOMO-12(
b
) / LUMO(
b
)
b
Cu(d
Cu(d
p
p
) / Cu(d
) / Cu(d
p
p
)
)
b
) / LUMO(
)
b
(49%)HOMO-1(
(28%)HOMO-3(
(26%)HOMO-4(
(34%)HOMO-6(
(33%)HOMO-2(
b
b
b
b
b
) / LUMOþ1(
)
)
L(
L(
L(
L(
L(
p
p
p
p
p
) / L(p*
)
) / LUMO(
) / LUMO(
) / LUMO(
b
b
b
)
)
)
) / L(
) / L(
) / L(
p
p
p
*)/Cu(d
*)/Cu(d
*)/Cu(d
p)
p)
p)
) / LUMOþ1(
b
) / L(p*
)

98
A.K. Pramanik et al. / Journal of Molecular Structure 1099 (2015) 92e98
(2000) 217.
Acknowledgment
[21] W.C. Wolsey, J. Chem. Educ. 50 (1973) A335.
[22] L.J. Farrugia, J. Appl. Cryst. 45 (2012) 849.
[23] G.M. Sheldrick, Acta Crysallogr, Sect. A 64 (2008) 112.
[24] SAINT Plus, Data Reduction and Correction Program, v. 6.01, Bruker AXS,
Madison, Wisconsin, USA, 1998.
[25] Bruker APEX2, SAINT and SADABS, Bruker AXS Inc, Madison, Wisconsin, USA,
2010.
Financial support received from the Department of Science and
Technology, New Delhi, India (No. SB/EMEQe242/2013) is grate-
fully acknowledged. A. K. Pramanik and D. Sarkar acknowledge
CSIR, New Delhi, India for fellowship.
[26] L.J. Farrugia, ORTEP-3 for windows, J. Appl. Cryst. 30 (1997) 565.
[27] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam,
M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski,
R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador,
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2015.06.048.
References
[1] J. Koh, A.J. Greaves, Dyes Pigments 50 (2001) 117e126.
[2] N. Sekar, Colourage 46 (1999) 63e65.
[3] H.E. Katz, K.D. Singer, J.E. Sohn, C.W. Dirk, L.A. King, H.M. Gordon, J. Am. Chem.
Soc. 109 (1987) 6561e6563.
[4] S. Wang, S. Shen, H. Xu, Dyes Pigments 44 (2000) 195e198.
[5] K. Maho, T. Shintaro, K. Yutaka, W. Kazuo, N. Toshiyuki, T. Mosahiko, Jpn. J.
Appl. Phys. 42 (2003) 1068e1075.
[6] G. Hallas, J.H. Choi, Dyes Pigments 40 (1999) 119e129.
[7] P. Gregory, D.R. Waring, G. Hallos, The Chemistry and Application of Dyes,
Plenum Press, London, 1990, pp. 18e20.
[8] S. Wu, W. Qian, Z. Xia, Y. Zou, S. Wang, S. Shen, Chem. Phys. Lett. 330 (2000)
535e540.
[9] P. Gilli, V. Bertolasi, L. Pretto, A. Lycka, G. Gilli, J. Am. Chem. Soc. 124 (2002)
13554e13567.
[10] R.C. Cox, E. Buncel, in: S. Patai (Ed.), The Chemistry of the Hydrazo, Azo and
Azoxy Groups, Wiley, Chichester, 1970, p. 838.
[11] J.A. Connor, R.J. Kennedy, M.H. Dawes, M.B. Hursthouse, N.P.C. Walker,
J. Chem. Soc. Perkin Trans. 2 (1990) 203e207.
[12] A.C. Olivieri, R.B. Wilson, I.C. Paul, D.Y. Curtin, J. Am. Chem. Soc. 111 (1989)
5525e5532.
[13] G. Gilli, F. Belucci, V. Ferreti, V. Bertolasi, J. Am. Chem. Soc. 111 (1989)
1023e1028.
[14] V. Bertolasi, P. Gilli, V. Ferreti, G. Gilli, J. Am.Chem. Soc. 113 (1991)
4917e4925.
[15] G. Gilli, V. Bertolasi, V. Ferreti, P. Gilli, Acta Crystallogr. Sect. B 49 (1993)
564e576.
[16] V. Bertolasi, P. Gilli, V. Ferreti, G. Gilli, Chem. Eur. J. 2 (1996) 925e934.
[17] V. Bertolasi, V. Ferreti, G. Gilli, Y.M. Issa, O.E. Sherif, J. Chem. Soc. Perkin Trans.
2 (1993) 2223e2228.
[18] V. Bertolasi, L. Nanni, P. Gilli, V. Ferreti, G. Gilli, Y.M. Issa, O.E. Sherif, New. J.
Chem. 18 (1994), 251e161.
€
J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz,
J. Cioslowski, D.J. Fox, Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford
CT, 2009.
[28] A.D. Becke, J. Chem. Phys. 98 (1993) 5648e5652.
[29] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785e789.
[30] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270e283.
[31] W.R. Wadt, P.J. Hay, J. Chem. Phys. 82 (1985) 284e298.
[32] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299e310.
[33] R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett. 256 (1996) 454e464.
[34] R.E. Stratmann, G.E. Scuseria, M.J. Frisch, J. Chem. Phys. 109 (1998)
8218e8224.
[35] M.E. Casida, C. Jamorski, K.C. Casida, D.R. Salahub, J. Chem. Phys. 108 (1998)
4439e4449.
[36] V. Barone, M. Cossi, J. Phys. Chem. A 102 (1998) 1995e2001.
[37] M. Cossi, V. Barone, J. Chem. Phys. 115 (2001) 4708e4717.
[38] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 24 (2003)
669e681.
[39] N.M. O'Boyle, A.L. Tenderholt, K.M. Langner, J. Comput. Chem. 29 (2008)
839e845.
[40] S. Sarkar, A. Patra, M.G.B. Drew, E. Zangrando, P. Chattopadhyay, Polyhedron
28 (2009) 1.
[41] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc.
Dalton Trans. (1984) 1349e1356.
[42] G. Murphy, P. Nagle, B. Murphy, B. Hathaway, J. Chem. Soc. Dalton Trans.
(1997) 2645e2652.
[43] G. Murphy, C. Murphy, B. Murphy, B. Hathaway, J. Chem. Soc. Dalton Trans.
(1997) 2653e2660.
[44] G. Murphy, C. O'Sullivan, B. Murphy, B. Hathaway, Inorg. Chem. 37 (1998)
240e248.
[45] D.-M. Feng, H.-Y. He, H.-X. Jin, L.-G. Zhu, Z. Kristallogr, New. Cryst. Struct. 220
(2005) 429e430.
[19] V. Bertolasi, L. Pretto, G. Gilli, P. Gilli, Acta Crystallogr. Sect. B 62 (2006)
850e863.
[20] P. Chattopadhyay, Y.H. Chiu, J.M. Lo, C.S. Chung, T.H. Lu, Appl. Radiat. Isot. 52