Synthesis, crystal structures, spectral studies and reactivity of square planar copper(II) complexes containing Schiff base ligand

Article abstract of DOI:10.1080/00958972.2013.764414

The reactions of HL¹ [2-((2-(benzylthio)phenylimino)methyl) phenol] and HL² [3-((2-(benzylthio)phenylimino)methyl)-2-hydroxy-5- methylbenzaldehyde] separately with Cu(OAc)₂·H₂O afforded new Cu(II) complexes [Cu(

Full text of DOI:10.1080/00958972.2013.764414

This article was downloaded by: [North Carolina State University]
On: 03 April 2013, At: 23:27
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis, crystal structures, spectral
studies and reactivity of square planar
copper(II) complexes containing Schiff
base ligand
Poulami Pattanayak a , Jahar Lal Pratihar b , Debprasad Patra c
Chia-Her Lin d , Paula Brandão e , Dasarath Mal e & Vitor Felix e
,
a Department of Chemistry, University of Kalyani, Kalyani, India
b Department of Chemistry, Kandi Raj College, Murshidabad, India
c Department of Chemistry, East Calcutta Girls’ College, Kolkata,
India
d Department of Chemistry, Chung Yuan Christian University,
Chung-Li 320, Taiwan
e Department of Chemistry/CICECO, University of Aveiro, Aveiro,
Portugal
Accepted author version posted online: 18 Jan 2013.Version of
record first published: 25 Feb 2013.
To cite this article: Poulami Pattanayak , Jahar Lal Pratihar , Debprasad Patra , Chia-Her Lin ,
Paula Brandão , Dasarath Mal & Vitor Felix (2013): Synthesis, crystal structures, spectral studies
and reactivity of square planar copper(II) complexes containing Schiff base ligand, Journal of
Coordination Chemistry, 66:4, 568-579
To link to this article: http://dx.doi.org/10.1080/00958972.2013.764414
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-
conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary

sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Journal of Coordination Chemistry
Vol. 66, No. 4, 20 February 2013, 568–579
Synthesis, crystal structures, spectral studies and reactivity of
square planar copper(II) complexes containing Schiff base
ligand
POULAMI PATTANAYAK*†, JAHAR LAL PRATIHAR*‡, DEBPRASAD PATRA§,
CHIA-HER LIN{, PAULA BRANDÃOk, DASARATH MALk and VITOR FELIXk
†Department of Chemistry, University of Kalyani, Kalyani, India
‡Department of Chemistry, Kandi Raj College, Murshidabad, India
xDepartment of Chemistry, East Calcutta Girls’ College, Kolkata, India
{Department of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan
kDepartment of Chemistry/CICECO, University of Aveiro, Aveiro, Portugal
(Received 4 July 2012; in final form 24 October 2012)
The reactions of HL1 [2-((2-(benzylthio)phenylimino)methyl)phenol] and HL2 [3-((2-(benzylthio)
phenylimino)methyl)-2-hydroxy-5-methylbenzaldehyde] separately with Cu(OAc)2·H2O afforded
new Cu(II) complexes [Cu(L1)(OAc)] (1) and [Cu(L2)2] (2), respectively. These are characterized
by microanalytical data and spectroscopic studies. UV–vis spectra of the complexes show intense
low-energy transitions ꢀ 420 nm which are ligand to metal charge transfer (LMCT) transitions.
The single-crystal X-ray structures were determined for 1 and 2. Reactions of [Cu(L1)(OAc)] (1)
with Nꢁ3 , SCN– and NOꢁ2 show the replacement of weakly coordinated acetate yielding [Cu(L1)
(N3)], [Cu(L1)(SCN)] and [Cu(L1)(NO2)], respectively. Unequivocal characterization of the substi-
tuted products has been done by single-crystal X-ray study of [Cu(L1)(N3)]. HL2 and its Cu(II)
complex exhibited low-intensity emission bands at ꢀ575 nm upon excitation at 375 nm and at
420 nm, respectively. Redox properties of the complexes were determined electrochemically.
Density functional theory (DFT) computations have been carried out to explain the spectroscopic
and redox properties of the complexes.
Keywords: Copper(II); Crystal structure; Ligand substitution; Redox; DFT
1. Introduction
Transition metal complexes of Schiff bases derived from salicylaldehyde/substituted
salicylaldehydes have received attention for applications in catalysis [1–5], magnetism
[6–9], molecular architectures [10–13], materials chemistry and biological activity [14–17].
Metal complexes of (O, N, S) chelating Schiff bases have specific properties, for
example, electrochemistry [18–21], photochromism [22], asymmetric catalysis [23,24],
oxo-transfer reactions [25–28] and antimicrobial activities [29–32]. Metal complexes of
thiosemicarbazones, dithiocarbazic acid and the Schiff base derived from its s-methyl ester
show a variety of biological activities against bacteria, fungi and certain type of tumors
*Corresponding authors. Email: pparka@rediffmail.com (P. Pattanayak); jlpr@rediffmail.com (J.L. Pratihar).
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2013.764414

Square planar copper(II)
569
[15,33–35]. The O,N,S donors, where “O” is phenolato oxygen, “N” is azomethine
nitrogen and “S” is thioether sulfur, have not been utilized to explore the chemistry of
transition metal ions. The relevance of copper(II) chemistry of O, N, and S donor ligands
prompted us to design new tridentate ligands having phenolato, azomethine and thioether
donors to copper.
In this article, we describe the preparation, structures, reactivity, spectroscopic and elec-
trochemical properties of copper complexes incorporating bi or tridentate Schiff bases con-
taining nitrogen, oxygen and sulfur donors. The syntheses of HL1 and HL2 and their
reactions with Cu(II) acetate are described here. Complex 1 underwent ligand substitution
with NaN3, NH4SCN, and NaNO2. The ligands and metal complexes are characterized by
1
UV–vis, IR and H NMR. Single-crystal X-ray studies on [Cu(L1)(OAc)], [Cu(L2)2] and
[Cu(L1)(N3)] were done. Photoluminescence of HL2 and [Cu(L2)2] has been investigated.
The redox properties and plausible nature of the redox orbitals are described on the basis
of single-point DFT calculations.
2. Experimental
2.1. Materials
The solvents were of reagent grade (E. Marck, Kolkata, India) and were purified and dried
by reported procedure [36]. Copper acetate monohydrate, benzyl chloride, salicylaldehyde,
sodium azide, ammonium thiocyanate, and sodium nitrite were purchased from Emark, India.
2-Aminothiophenol was purchased from Aldrich. 2-(Benzylthio)aniline and 2-hydroxy-5-
methylbenzene-1,3-dialdehyde were prepared following reported procedures [37,38].
2.2. Physical measurements
Microanalyses (C, H, N) were performed using a Perkin-Elmer 2400 C, H, N, S/O series
II elemental analyzer. Infrared spectra were recorded on a Perkin-Elmer L120-00A FT-IR
spectrometer with the samples prepared as KBr pellets. UV–vis spectra were recorded on a
1
Shimadzu UV-1800 PC spectrophotometer. H NMR spectra were obtained on Bruker 400
NMR spectrometers in CDCl3 using TMS as the internal standard. Emission spectra were
recorded with a Perkin Elmer LS-55 Luminescence Spectrometer. Electrochemical mea-
surements were made under dinitrogen using a CH instruments model 600D potentiostat.
A platinum disk working electrode, a platinum wire auxiliary electrode and an aqueous
saturated calomel reference electrode (SCE) were used in a three-electrode configuration.
All electrochemical data were collected at 298 K and are uncorrected for junction
potentials.
2.3. DFT calculations
Using the X-ray coordinates of [Cu(L1)(OAc)], [Cu(L1)(N3)] and [Cu(L2)2], ground state
electronic structure calculations have been carried out using DFT [39] methods with the
Orca 2.7 program [39]. Becke’s hybrid function [40] with the Lee–Yang–Parr correlation
function [41] was used throughout the study. LANL2DZ valence and effective core poten-
tial functions were used. All energy calculations were performed using the self-consistent
field “tight” option of the Orca 2.7 program to ensure sufficiently well converged values
for state energies.

570
P. Pattanayak et al.
2.4. Synthesis of HL1 and HL2
HL1 [2-((2-(benzylthio)phenylimino)methyl)phenol] and HL2 [3-((2-(benzylthio)phenylimi-
no)methyl)-2-hydroxy-5-methylbenzaldehyde] were synthesized following a common
procedure. Details of the synthesis for HL1 are given below.
2-(Benzylthio)aniline (1000 mg, 4.65 mmol) was dissolved in 30 ml ethanol, salicylalde-
hyde (567 mg, 4.65 mmol) was added to it and the mixture was refluxed for 5 h, filtered,
the filtrate collected in a beaker and solvent allowed to evaporate slowly. The yellow crys-
talline product at the bottom of the beaker was collected, washed with ethanol and dried
over CaCl2 in a desiccator. Yield was 80%. Anal. Calcd for C20H17NOS (319.17): C,
75.20; H, 5.37; N, 4.39%. Found: C, 75.37; H, 5.32; N, 4.24. UV/Vis spectrum (CH2Cl2)
λmax (ɛ, Mꢁ1cmꢁ1) = 350 (15,770), 270 (32,760). IR (KBr pellets, cmꢁ1): ν = 3215 (O–H),
1
1610 (CH=N), 1556 (C–O), 750 (C–S). H NMR CDCl3: δ 13.11 (s, 1H), 8.47 (s, 1H),
7.30 (t, 3H), 7.21–7.08 (m, 8H), 7.00 (d, 1H), 6.86 (t, 1H), 4.02 (s, 2H).
HL2: Yield was 85%. Anal. Calcd for C22H19NO2S (361.20): C, 73.09; H, 5.30; N,
3.88%. Found: C, 73.21; H, 5.42; N, 4.04. UV/Vis spectrum (CH2Cl2) λmax (ɛ, Mꢁ1cmꢁ1
)
= 375 (12,200), 255 (29,700). IR (KBr pellets, cmꢁ1): ν = 3352 (O–H), 1682 (CHO), 1621
1
(CH=N), 1593 (C–O), 752 (C–S). H NMR (CDCl3, ppm) δ: 13.84 (s, 1H), 10.59 (s, 1H),
8.53 (s, 1H), 7.75 (s, 1H), 7.52 (s, 1H), 7.37–7.39 (d, 1H), 7.31–7.33 (d, 2H), 7.19–7.28
(m, 5H), 7.13–7.16 (d, 1H), 4.14 (s, 2H), 2.37 (s, 3H).
2.5. Synthesis of complexes
2.5.1. [Cu(L1)(OAc)](1). To a solution of HL1 (1000 mg, 3.13 mmol) in 100 mL metha-
nol (625 mg, 3.13 mmol) Cu(OAc)2·H2O was added. Immediately the color of the solution
changed to olive green was stirred for 5 h at room temperature and kept for crystallization.
After a few days, dark crystals were obtained. Yield: 90%. Anal. C22H19NO3SCu (441):
Calcd C, 59.87; H, 4.34; N, 3.18. Found: C, 59.67; H, 4.52; N, 3.12%. UV/Vis spectrum
(CH2Cl2) λmax (ɛ, Mꢁ1cmꢁ1) = 425 (10,650), 305 (24,400). IR (KBr pellets, cmꢁ1):
ν = 1605 (CH=N), 1389 (OAc), 1529 (C–O), 756 (C–S).
2.5.2. [Cu(L2)2](2). To a solution of HL2 (361 mg, 1 mmol) in 25 mL methanol (200 mg,
1 mmol) Cu(OAc)2·H2O was added. Immediately the color of the solution changed to
green, was stirred for 4 h at room temperature and kept for crystallization. After a few
days, dark crystals were obtained. Yield: 75%. Anal. Calcd for C44H36N2O4S2Cu (784.44):
C, 67.31; H, 4.62; N, 3.57. Found: C, 67.16; H, 4.73; N, 3.61%. UV–vis λmax (dichloro-
methane, nm) ɛ /Mꢁ1, cmꢁ1): 420 (19,270), 250 (68,150). IR (KBr pellets, cmꢁ1):
ν = 1668 (CHO), 1617 (CH=N), 1537 (C–O), 746 (C–S).
2.5.3. Syntheses of [Cu(L1)(N3)] (3), [Cu(L1)(NCS)] (4) and [Cu(L1)(NO2)] (5). [Cu
(L1)(N3)], [Cu(L1)(NCS)] and [Cu(L1)(NO2)] were prepared by adding methanol solution
(10 mL) of sodium azide (30 mg, 0.45 mmol), ammonium thiocyanate (35 mg, 0.45 mmol)
or sodium nitrite (31 mg, 0.45 mmol), respectively, to methanol solution (10 mL) of [Cu
(L1)(OAc)] (200 mg, 0.45 mmol); the mixture was stirred for 3 h. In all cases, dark green
crystals were obtained after a few days.

Square planar copper(II)
571
Complex 3 (Yield was 90%). Anal. Calcd for C20H16N4OSCu (423.99): C, 56.61; H,
3.80; N, 13.21%. Found: C, 56.37; H, 3.71; N, 13.38. UV–vis λmax (dichloromethane, nm)
ɛ/Mꢁ1, cm-1): 425 (10,230), 315 (22,050). IR (KBr pellets, cmꢁ1): ν = 1607 (CH=N), 2037
(N3), 1531 (C–O), 759 (C–S).
Complex 4 (Yield was 90%). Anal. Calcd for C21H16N2OS2Cu (439.84): C, 57.30; H,
3.67; N, 6.37%. Found: C, 57.44; H, 3.78; N, 6.14. UV–vis λmax (dichloromethane, nm) ɛ
/Mꢁ1, cmꢁ1): 435 (9600), 315 (23,500). IR (KBr pellets, cmꢁ1): ν = 1603 (CH=N), 2087
(NCS), 1533 (C–O), 754 (C–S).
Complex 5 (Yield was 90%). Anal. Calcd for C20H16N2O3SCu (427.97): C, 56.08; H,
3.77; N, 6.54%. Found: C, 56.23; H, 3.65; N, 6.31. UV–vis λmax (dichloromethane, nm) ɛ
/Mꢁ1, cmꢁ1): 415 (7540), 300 (17,300). IR (KBr pellets, cmꢁ1): ν = 1605 (CH=N), 1271
(NO2), 1531 (C–O), 754 (C–S).
2.6. Crystallography
Single crystals of [Cu(L1)(OAc)], [Cu(L2)2] and [Cu(L1)(N3)] were grown by slow evapora-
tion of methanol solution at 298 K. Data were collected by ω-scan on a Bruker Smart CCD
diffractometer with Mo-Kα radiation monochromated by graphite crystal. Structure solution
was done by direct methods with SHELXS–97 [42,43]. Full matrix least square refinements
on F2 were performed using SHELXL–97 [42,43]. All non-hydrogen atoms were refined
anisotropically using reflections I > 2σ (I). All hydrogens were included at calculated
positions. Data collection parameters and relevant crystal data are collected in table 1.
3. Results and discussion
3.1. Synthesis
HL1 and HL2 are synthesized by condensation of 2-(benzylthio)aniline and salicylaldehyde
and 2-hydroxy-5-methylbenzene-1,3-dialdehyde in dry ethanol (scheme 1), respectively.
Table 1. Crystallographic data for 1, 2 and 3.
Chemical formula
C22H19CuNO3S
C44H36CuN2O4S2
C20H16CuN4OS
Formula weight
441.00
784.44
Monoclinic
C2/c (No. 15)
22.4537(7)
13.3246(4)
14.4452(4)
90
121.819(10)
90
0.71073
3672.32(19)
1628
423.99
Crystal system
Space group
a/Å
b/Å
c/Å
α/°
β/°
γ/°
Triclinic
P-1 (No. 2)
10.1015(5)
12.1951(6)
15.5937(7)
81.199(3)
80.102(3)
89.735(3)
0.71073
1869.63(16)
908
Triclinic
P-1 (No. 2)
9.5322(4)
12.3638(5)
15.6199(7)
77.509(2)
80.512(2)
89.289(2)
0.71073
1772.19(13)
868
λ/Å
V/Å3
F(000)
Z
4
4
4
T/K
296
1.567
1.304
0.0863
0.2430
1.02
150
1.419
0.756
0.0405
0.1263
0.97
150
1.589
1.368
0.0390
0.1101
1.00
D/mg/mꢁ3
μ/mmꢁ1
R1 (all data)
wR2[I > 2(I)]
GOF

572
P. Pattanayak et al.
R1
R2
OH
R2
EtOH
Reflux
NH2
N
S
S
+
R1
CHO
OH
R1 = R2 = H for HL1
R1 = CH3, R2 = CHO for HL2
Scheme 1. Synthesis of HL1 and HL2.
Reaction between HL and Cu(OAc)2·H2O in MeOH gave the tridentate (O,N,S) and biden-
tate (O, N) bis chelate complexes of composition [Cu(L1)(OAc)] (1) and [Cu(L2)2] (2)
(scheme 2). We tried to obtain (O, N, S) coordination of HL2 by changing the metal/ligand
ratio, but we always obtained bidentate (O, N) coordination. The subtle change in binding
mode of HL2 may be due to presence of –CHO and –CH3 in 3 and 5 positions, respec-
tively, of the phenyl ring of aldehydic component of aldimine. The compounds are neutral
and their composition is supported by microanalytical data. The structures of [Cu(L1)
(OAc)] and [Cu(L2)2] have been established by single-crystal X-ray diffraction study.
Reactions of [Cu(L1)(OAc)] (1) with sodium azide, ammonium thiocyanate and sodium
nitrite gives [Cu(L1)(N3)] (3), [Cu(L1)(NCS)] (4) and [Cu(L1)(NO2)] (5), respectively
(scheme 3). Formation of 3–5 from 1 clearly indicates that the weakly coordinated acetate
can be replaced easily by stronger coordinating Nꢁ3 , SCN– and NO2ꢁ. Single-crystal X-ray
study of [Cu(L1)(N3)] has been done for the unequivocal characterization.
3.2. Characterizations
3.2.1. UV–vis spectra. HL1, HL2 and 1–5 are soluble in common organic solvents with
yellow and light green color, respectively. UV–vis spectra of the ligand and complexes
were recorded in dichloromethane. High-energy transitions at 320 nm are associated with
ligand centered πꢁπ⁄ transitions [21]. A low-energy absorption near 425 nm has been
assigned to LMCT transition, consistent with DFT results (see below). UV–vis spectra of
3–5 were very similar with 1. UV–vis spectra of all the compounds are deposited as ESI
(figures S1–S7) and data are collected in the experimental section.
R2
R2
R1
O
R1
O
R2
R1
OAc
S
Cu (OAc)2
MeOH
Cu (OAc)2
MeOH
N
Cu
S
Cu
OH
N
N
O
S
N
S
R2
R1
Cu(L1)(OAc)
R1 = R2 = H
[Cu(L2)2]
R1 = CHO, R2 = CH3
1
2
Scheme 2. Synthesis of 1 and 2.

Square planar copper(II)
573
O
OAc
Cu
N
S
[Cu(L1)(OAc)]
1
NaN3
NaNO2
NH4SCN
[Cu(L1)(NO2)]
5
[Cu(L1)(N3)]
3
[Cu(L1)(NCS)]
4
Scheme 3. Synthesis of 3–5.
3.2.2. Infrared spectra. The free Schiff bases HL1 and HL2 show strong bands at 1621
and 1610 cmꢁ1, characteristic of the azomethine ν(C=N) [20]. The ν(C=N) shifts to lower
frequency in all the complexes 1617–1603 cmꢁ1, indicating coordination of the Schiff
bases through the azomethine nitrogen. Phenolic C–O at 1282 and 1261 cmꢁ1 [20] in HL1
and HL2 shifts to higher frequency, 1382–1394 cmꢁ1, indicating coordination through the
phenolic oxygen. In IR spectra of 3 a strong band at 2055 cmꢁ1 indicates the presence of
coordinated azide [44]. Similarly, bands at 2077 and 1271 cmꢁ1 in 4 and 5 indicate the
presence of the N-coordinated thiocyanate and O-coordinated nitrite [44], but no acetate
band near 1100 cmꢁ1 was observed. The ν(C–S) near 750 cmꢁ1 indicates coordination of
the thio-benzyl group. IR spectral data of HL1 and HL2 and their corresponding
complexes are given in the experimental section and the spectra are deposited as ESI
(figures S8–S14).
1
3.2.3. 1H NMR spectra. Free Schiff bases HL1 and HL2 have been characterized by H
NMR spectra and the data are given in the experimental section (figures S15 and S16). In
HL1 and HL2, the phenolic –OH appears as a broad singlet at 13.11 and 13.84 ppm,
respectively [20]. The broadness is due to hydrogen bonding between phenolic –OH and
azomethine (–CH=N–) hydrogen. The azomethine protons in HL1 and HL2 are sharp sing-
lets at 8.47 and 8.53 ppm, respectively [20]. A sharp singlet at 4.02 and 4.14 ppm for HL1
and HL2, respectively, is assigned for benzyl protons of the ligands. All the aromatic
protons are 7.75–6.86 ppm. The –CHO and –CH3 signals in HL2 are at 10.59 and
2.37 ppm, respectively.
3.2.4. X-ray crystal structure. [Cu(L1)(OAc)] and [Cu(L1)(N3)]. Suitable crystals of [Cu
(L1)(OAc)] and [Cu(L1)(N3)] were grown by slow evaporation of mother liquor. The X-ray
structures of [Cu(L1)(OAc)] and [Cu(L1)(N3)] were determined and the perspective view

574
P. Pattanayak et al.
Figure 1. ORTEP plot of 1 with atom-numbering scheme. Hydrogens are omitted for clarity.
Figure 2. ORTEP plot of 3 with atom-numbering scheme. Hydrogens are omitted for clarity.

Square planar copper(II)
575
of the molecules along with the atom numbering scheme are shown in figures 1 and 2 and
selected bond distances and angles are collected in tables 2 and 4. The asymmetric unit
contains two molecules, both molecules have the same structural parameters for
[Cu(L1)(OAc)] and [Cu(L1)(N3)], respectively. So structure analysis of one molecule is
considered in each case. The geometry about copper(II) is distorted square planar where
uni-negative L1 binds tridentate (O, N, S). An acetate (for 1) and azide (for 3) satisfies the
four coordination. The three donors are deprotonated phenolic oxygen, imine nitrogen and
sulfur. The Cu1–S1, Cu1–N1, Cu1–O1, Cu1–O2 and C7–N1 lengths (2.3142(15), 1.952
(5), 1.904(4), 1.955(4) and 1.305(7) Å, respectively) for 1 and the Cu1–S1, Cu1–N1,
Cu1–O1, Cu1–N2 and C7–N1 lengths (2.3229(7), 1.961(2), 1.898(2), 1.962(2) and 1.306
(3), respectively) for 3 are within the normal range [45–48]. The geometries about Cu(II)
are planar (mean deviation 0.075 Å for 1 and 0.062 Å for 3).
Table 2. Selected bond distances (Å) and angles (°) for 1.
Distances
Cu1–S1
Cu1–O1
Cu1–O2
C6–C7
O1–C1
O3–C21
N1–C7
2.3142(15)
1.904(4)
1.955(4)
1.422(7)
1.310(7)
1.250(7)
1.305(7)
Cu1–N1
C8–C13
S1–C13
S1–C14
O2–C21
N1–C8
1.952(5)
1.389(7)
1.764(5)
1.842(6)
1.290(7)
1.426(7)
1.510(8)
C14–C15
Angles
S1–Cu1–O1
S1–Cu1–O2
S1–Cu1–N1
O1–Cu1–N1
O2–Cu1–N1
Cu1–S1–C13
N1–C8–C13
Cu1–O1–C1
177.42(13)
86.77(13)
86.77(13)
94.88(17)
169.33(18)
95.76(17)
117.4(4)
O1–Cu1–O2
Cu1–N1–C7
Cu1–N1–C8
C7–N1–C8
91.30(17)
122.2(4)
118.3(3)
119.1(5)
126.6(5)
98.34(18)
103.8(3)
106.9(4)
N1–C7–C6
Cu1–S1–C14
C13–S1–C14
Cu1–O2–C21
125.6(4)
Table 3. Selected bond distances (Å) and angles (°) for 2.
Distances
Cu1–O1
S1–C15
O1–C1
N1–C9
C16–C17
C4–C7
1.905(2)
1.775(3)
1.305(3)
1.295(4)
1.506(4)
1.512(5)
Cu1–N1
S1–C16
O2–C8
N1–C10
C2–C8
C6–C9
2.004(2)
1.829(4)
1.215(4)
1.437(4)
1.468(4)
1.438(5)
Angles
O1–Cu1–N1
O1–Cu1–O1#
O1–Cu1–N1#
O1#–Cu1–N1
Cu1–N1–C9
S1–C16–C17
89.38(9)
180.00
90.62(9)
90.62(9)
121.5(2)
109.9(3)
N1–Cu1–N1#
O1#–Cu1–N1#
C15–S1–C16
Cu1–O1–C1
Cu1–N1–C10
N1–C9–C6
180.00
89.38(9)
101.50(15)
123.46(16)
120.22(17)
125.5(2)

576
P. Pattanayak et al.
[Cu(L2)2]. Suitable crystals of [Cu(L2)2], for X-ray studies, were grown upon slow
evaporation of methanol solution. A perspective view of the molecular structure is shown
in figure 3. Selected bond distances and angles are collected in table 3. Each deprotonated
ligand binds bidentate (O, N) with each ligand symmetry equivalent to the other held
trans. The perfectly square planar CuN2O2 coordination (mean deviation 0.00 Å) is consis-
tent with Cu(II) and uninegative ligand. Cu1–N1, Cu1–O1 and C9–N1 lengths (2.004(2),
1.905(2) and 1.295(4) Å, respectively) are within the normal range [45–48]. The fragment
containing C9, N1, C6, C1, C2, C3, C4, C5 and O1 is satisfactorily planar (mean devia-
tion 0.063 Å) and the dihedral angle with the CuN2O2 plane is 21.6°. Therefore the metal-
locycle has an envelope conformation (figure 4) due to steric crowding around copper
[49]. The metal–ligand bonding in six-membered analogous boat-shaped chelate ring
Figure 3. ORTEP plot of 2 with atom-numbering scheme. Hydrogens are omitted for clarity.
Table 4. Selected bond distances (Å) and angles (°) for 3.
Distances
Cu1–S1
Cu1–O1
Cu1–N1
C6–C7
N1–C8
N2–N3
2.3229(7)
1.898(2)
1.961(2)
1.421(4)
1.431(3)
1.198(3)
Cu1–N2
S1–C14
S1–C13
O1–C1
N1–C7
N3–N4
1.962(2)
1.850(3)
1.769(3)
1.312(3)
1.306(3)
1.157(3)
Angles
S1–Cu1–O1
S1–Cu1–N1
S1–Cu1–N2
O1–C1–C6
Cu1–S1–C14
C13–S1–C14
Cu1–N1–C7
Cu1–N2–N3
178.22(6)
86.35(6)
87.44(8)
124.0(2)
98.12(9)
103.63(12)
122.56(17)
123.9(2)
O1–Cu1–N1
O1–Cu1–N2
N1–Cu1–N2
N2–N3–N4
Cu1–S1–C13
Cu1–O1–C1
S1–C14–C15
94.62(8)
91.47(10)
172.37(10)
176.4(3)
96.32(9)
125.63(17)
112.5(2)

Square planar copper(II)
577
O
N
C
C
C
C
N
O
Cu
C
C
Figure 4. Envelope-shaped structure of 2.
should be appropriately described by σ and π interactions [50], but for less puckered
systems (in this case) the π interactions are unlikely to be significant [51].
3.2.5. Fluorescence spectra. Fluorescent properties of HL2 and its complex with Cu(II)
in dichloromethane exhibit low-intensity emission bands at ꢀ575 nm upon excitation at
375 nm for HL2 and at 420 nm for its complex (figures S17 and S18). The usual quenching
effect of Cu(II) in the emission of ligand was not noticed. The reason behind this is cur-
rently under investigation.
3.2.6. Electrochemistry. Electrochemical behavior of [Cu(L1)(OAc)] and [Cu(L2)2] was
investigated in dichloromethane/acetonitrile mixed solvent (0.1 M TBAP) by cyclic voltam-
metry with a scan rate of 50 mV sꢁ1 (figures S19 and S20). The cyclic voltammogram of
[Cu(L1)(OAc)] displayed one cathodic peak and one anodic peak at ꢁ0.5 V and 0.75 V,
Figure 5. Surface plots of HOMO, SOMO, LUMO and LUMO + 1 of Cu(L)(OAc) (1), Cu(L)2 (2) and Cu(L)
(N3) (3).

578
P. Pattanayak et al.
while [Cu(L2)2] exhibited only one anodic peak at 0.63 V. According to DFT results the
composition of HOMO, SOMO, LUMO and LUMO + 1 (figure 5) of 1–3 are ligand
centered, indicating irreversible oxidation and reduction of ligand.
4. Conclusion
Copper complexes containing (ONS and ON) donors and their activities have been
reported [18–32,52–55] but O,N, and S donor ligands, where “O” is phenolato oxygen,
“N” is azomethine nitrogen and “S” is thioether sulfur, have not been reported. Newly syn-
thesized HL1 and HL2 afforded [Cu(L1)(OAc)] and [Cu(L2)2], respectively, upon reaction
with Cu(OAc)2, where HL1 binds tridentate (O,N,S) and HL2 bidentate (O,N). The subtle
change in binding mode of HL2 may be due to the presence of –CHO and –CH3 in 3 and
5 positions, respectively, of the phenyl ring of aldehydic component of aldimine. Acetate
substitution in 1 upon reaction with NaN3, NH4SCN and NaNO2 established weak
coordination of the acetate to Cu(II). Single-point DFT calculation shows that the redox
properties of the complexes are ligand centered.
Supplementary material
Figures S1–S14 show the UV/Vis and IR spectra and figures S15–S20 the 1H NMR
spectra, emission and cyclic voltammogram of the ligands and complexes. CCDC-806267,
872080 and 872081 contains the supplementary crystallographic data for [Cu(L1)(OAc)],
[Cu(L2)2] and [Cu(L1)(N3)]. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
Special thanks to Professor Surajit Chattopadhyay, University of Kalyani, for his valuable
suggestions throughout this study. The financial support from University Grants
Commission is gratefully acknowledged (under Minor Research Project, Sanction No. F.
PSW/067/2011-12). The necessary laboratory and infrastructural facility are provided by
the Department of Chemistry, Kandi Raj College and Department of Chemistry, University
of Kalyani.
References
[1] H. Mihara, Y. Xu, N.E. Shepherd, S. Matsunaga, M. Shibasaki. J. Am. Chem. Soc., 131, 8384 (2009).
[2] Z. Chen, K. Yakura, S. Matsunaga, M. Shibasaki. Org. Lett., 10, 3239 (2008).
[3] S. Handa, V. Gnanadesikan, S. Matsunaga, M. Shibasaki. J. Am. Chem. Soc., 132, 4925 (2010).
[4] C.-M. Che, H-L. Kwong, W-C. Chu, K-F. Cheng, W-S. Lee, H-S. Yu, C-T. Yeung, K-K. Cheung. Eur. J.
Inorg. Chem., 1456 (2002).
[5] J.-Q. Wu, L. Pan, Y.-G. Li, S.-R. Liu, Y.-S. Li. Organometallics, 28, 1817 (2009).
[6] A. Burkhardt, A. Buchholz, H. Görls, W. Plass. Eur. J. Inorg. Chem., 3400 (2006).
[7] M. Yuan, F. Zhao, W. Zhang, Z.-M. Wang, S. Gao. Inorg. Chem., 46, 11235 (2007).
[8] C. Maxim, F. Tuna, A.M. Madalan, N. Avarvari, M. Andruh. Cryst. Growth Des., 12, 1654 (2012).
[9] C. Yang, Q.-L. Wang, Y. Ma, G.-T. Tang, D.-Z. Liao, S.-P. Yan, G.-M. Yang, P. Cheng. Inorg. Chem., 49,
2047 (2010).
[10] G. Zhang, G. Yang, J.S. Ma. Cryst. Growth Des., 6, 1897 (2006).
[11] E.N. Chygorin, O.V. Nesterova, J.A. Rusanova, V.N. Kokozay, V.V. Bon, R. Boča, A. Ozarowski. Inorg.
Chem., 51, 386 (2012).

Square planar copper(II)
579
[12] K.G. Vladimirova, A.Y. Freidzon, O.V. Kotova, A.A. Vaschenko, L.S. Lepnev, A.A. Bagatur’yants, A.G.
Vitukhnovskiy, N.F. Stepanov, M.V. Alfimov. Inorg. Chem., 48, 11123 (2009).
[13] Y.-Y. Ge, G.-B. Li, H.-C. Fang, X.-L. Zhan, Z.-G. Gu, J.-H. Chen, F. Sun, Y.-P. Cai, P.K. Thallapally. Cryst.
Growth Des., 10, 4987 (2010).
[14] J.P. May, R. Ting, L. Lermer, J.M. Thomas, Y. Roupioz, D.M. Perrin. J. Am. Chem. Soc., 126, 4145 (2004).
[15] M.R. Maurya, S. Khurana, Shailendra, A. Azam, W. Zhang, D. Rehder. Eur. J. Inorg. Chem., 1966 (2003).
[16] M.A. Ali, A.H. Mirza, R.J. Butcher, M.T.H. Tarafder, T.B. Keat, A.M. Ali. J. Inorg. Biochem., 92, 141
(2002).
[17] A.T. Chaviara, E.E. Kioseoglou, A.A. Pantazaki, A.C. Tsipis, P.A. Karipidis, D.A. Kyriakidis, C.A. Bolos. J.
Inorg. Biochem., 102, 1749 (2008).
[18] A. Rana, R. Dinda, P. Sengupta, S. Ghosh, L.R. Falvello. Polyhedron, 21, 1023 (2002).
[19] A. Rana, R. Dinda, S. Ghosh, A.J. Blake. Polyhedron, 22, 3075 (2003).
[20] S. Durmus, A. Atahan, M. Zengin. Spectrochim. Acta, Part A, 84, 1 (2011).
[21] B. Turner, S. Swavey. Inorg. Chem. Commun., 10, 209 (2007).
[22] A. Ohshima, A. Momotake, T. Arai. Photochem. Photobiol. A, 162, 473 (2004).
[23] K. Chichak, U. Jacquemard, N.R. Branda. Eur. J. Inorg. Chem., 2, 357 (2002).
[24] M. Muthu Tamizh, K. Mereiter, K. Kirchner, R. Karvembu. J. Organomet. Chem., 700, 194 (2012).
[25] S. Bhattacharjee, R. Bhattacharyya. J. Chem. Soc., Dalton Trans., 1357 (1992).
[26] S. Bhattacharjee, R. Bhattacharyya. J. Chem. Soc., Dalton Trans., 1151 (1993).
[27] S.K. Dutta, D.B. McConville, W.J. Youngs, M. Chaudhury. Inorg. Chem., 36, 2517 (1997).
[28] J. Pisk, B. Prugovečki, D. Matković-Čalogović, R. Poli, D. Agustin, V. Vrdoljak. Polyhedron, 33, 441
(2012).
[29] S.M. Abdallah, G.G. Mohamed, M.A. Zayed, M.S. Abou El-Ela. Spectrochim. Acta, Part A, 73, 833 (2009).
[30] Y.K. Gupta, S.C. Agarwal, S.P. Madnawat. J. Chem. Pharm. Res., 4, 746 (2012).
[31] M.R. Maurya, A. Kumar, A.R. Bhat, A. Azam, C. Bader, D. Rehder. Inorg. Chem., 45, 1260 (2006).
[32] S.K. Dutta, S. Samanta, D. Ghosh, R.J. Butcher, M. Chaudhury. Inorg. Chem., 41, 5555 (2002).
[33] R.P. John, A. Sreekanth, V. Rajakannan, T.A. Ajith, M.R. Prathapachandra Kurup. Polyhedron, 23, 2549
(2004).
[34] R. Prabhakaran, S.V. Renukadevi, R. Karvembu, R. Huang, J. Mautz, G. Huttner, R. Subashkumar, K. Nat-
arajan. Eur. J. Med. Chem., 43, 268 (2008).
[35] V.M. Leovac, G.A. Bogdanović, L.S. Jovanović, L. Joksović, V. Marković, M.D. Joksović, S.M. Denčić, A.
Isaković, I. Marković, F.W. Heinemann, S. Trifunović, I. Đalović. J. Inorg. Biochem., 105, 1413 (2011).
[36] D.D. Perrin, W.L.F. Armarego. Purification of Laboratory Chemicals, 3rd edn Edn, Pergamon, New York,
NY (1988).
[37] M.K. Paira, T.K. Mondal, E.L. Torres, J. Ribas, C. Sinha. Polyhedron, 29, 3147 (2010).
[38] B. Adhikary, A.K. Biswas, K. Nag. Polyhedron, 6, 1473 (1987).
[39] R.G. Parr, W. Yang. Density Functional Theory of Atoms and Molecules, Oxford University Press, Oxford
(1989).
[40] A.D. Becke. J. Chem. Phys., 98, 5648 (1993).
[41] C. Lee, W. Yang, R.G. Parr. Phys. Rev. B, 37, 785 (1998).
[42] G.M. Sheldrick. SHELXS-97, University of Göttingen, Göttingen (1990).
[43] G.M. Sheldrick. SHELXL-97, Program for the Refinement of Crystals Structures from Diffraction Data,
University of Göttingen, Göttingen (1997).
[44] S. Chattopadhyay, M.G.B. Drew, A. Ghosh. Inorg. Chim. Acta, 359, 4519 (2006).
[45] R. Balamurugan, M. Palaniandavar, H. Stoeckli-Evans, M. Neuburger. Inorg. Chim. Acta, 359, 1103 (2006).
[46] A.K. Singh, R. Mukherjee. Dalton Trans., 260 (2008).
[47] D. Cupertino, M. McPartlin, A.M. Zissimos. Polyhedron, 20, 3239 (2001).
[48] P. Pattanayak, D. Patra, C.-H. Lin, J.L. Pratihar. J. Chem. Res., 1, 1 (2012).
[49] P.B. Hitchcock, M.F. Lappert, S. Tian. J. Chem. Soc., Dalton Trans., 1945 (1997).
[50] M. Rahim, N.J. Taylor, S. Xin, S. Collins. Organometallics, 17, 1315 (1998).
[51] P.G. Hayes, W.E. Piers, L.W.M. Lee, L.K. Knight, M. Parvez, M.R.J. Elsegood, W. Clegg. Organomatallics,
20, 2533 (2001).
[52] S.A. Patil, V.H. Naik, A.D. Kulkarny, S.N. Unki, P.S. Babami. J. Coord. Chem., 64, 2688 (2011).
[53] R.J. Yadav, K.M. Vyas, R.N. Jadeja. J. Coord. Chem., 63, 1820 (2010).
[54] M. Kalanithi, M. Rajarajan, P. Tharmaraj. J. Coord. Chem., 64, 1436 (2011).
[55] M.B. Halli, V.B. Patil. J. Coord. Chem., 64, 3740 (2011).