Counter anion modulated variation of denticity of NNO donor Schiff base in copper(II) complexes: Isolation of a zwitterionic Schiff base as the metal complex

Article abstract of DOI:10.1016/j.poly.2013.06.007

Three copper(II) complexes [Cu(HL)₂(ClO₄)]ClO ₄H₂O (1), [Cu(L)DMF]ClO₄ (2) and [CuL(NCO)][Cu₂L₂ (NCO)₂] (3) [where HL = 2-[(2-Diethylamino-ethylimino)-methyl]-4-nitro-phenol, a tridentate Schiffbase] have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy and single-crystal X-ray diffraction studies. In complexes 2 and 3, the Schiff base is acting as a tridentate ligand. However, in complex 1, the Schiff base is present in its zwitterionic form. The denticity of the tridentate Schiff base has been modulated by the acidity of counter anions. Complexes 1 and 2 are mono-meric. Copper(II) assumes square pyramidal geometry in 1 (Addison parameter (τ) = 0.15) and square planar geometry in 2. The asymmetric unit of complex 3 consists of two crystallographically different double end-on cyanate bridged dimers, containing square pyramidal copper(II) {Addison parameter (s) = 0.157}. Complexes 1 and 3 crystallize in triclinic space group, P1 with cell dimensions a=11.3479(10), b=12.5198(9), c= 13.6640(12), α = 94.299(7)°, b = 97.281(7)° and γ = 116.007(6)° (for 1) and a = 11.6149(8), b = 11.8145(9), c= 13.8741(13), α = 65.524(6)°, b = 73.373(6)° and c = 63.857(5)° (for 3), whereas complex 2 crystallizes in monoclinic space group, P2_1/c with cell dimensions a = 7.5765(2), b=19.6005(6), c= 14.5861(4) and b = 102.679(1)° (for 2). The weak forces like lone pair ··· π / π ··· π/anion ··· π interactions lead to various supramolecular architectures.

Full text of DOI:10.1016/j.poly.2013.06.007

Polyhedron 62 (2013) 179–187
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Counter anion modulated variation of denticity of NNO donor Schiff base
in copper(II) complexes: Isolation of a zwitterionic Schiff base as the
metal complex
a
b
a,
⇑
Prasanta Kumar Bhaumik , Klaus Harms , Shouvik Chattopadhyay
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35032 Marburg, Germany
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Three copper(II) complexes [Cu(HL) (ClO )]ClO ÁH O (1), [Cu(L)DMF]ClO (2) and [CuL(NCO)][Cu2L2
2
4
4
2
4
Received 23 April 2013
Accepted 3 June 2013
Available online 20 June 2013
(
2
NCO) ] (3) [where HL = 2-[(2-Diethylamino-ethylimino)-methyl]-4-nitro-phenol, a tridentate Schiff-
base] have been synthesized and characterized by elemental analysis, IR and UV–Vis spectroscopy and
single-crystal X-ray diffraction studies. In complexes 2 and 3, the Schiff base is acting as a tridentate
ligand. However, in complex 1, the Schiff base is present in its zwitterionic form. The denticity of the tri-
dentate Schiff base has been modulated by the acidity of counter anions. Complexes 1 and 2 are mono-
meric. Copper(II) assumes square pyramidal geometry in 1 (Addison parameter (s) = 0.15) and square
planar geometry in 2. The asymmetric unit of complex 3 consists of two crystallographically different
Keywords:
Copper(II)
Schiff base
Crystal structure
Zwitterion
double end-on cyanate bridged dimers, containing square pyramidal copper(II) {Addison parameter
ꢀ
Supramolecular interaction
(
s
) = 0.157}. Complexes
a = 11.3479(10), b = 12.5198(9), c = 13.6640(12),
) and a = 11.6149(8), b = 11.8145(9), c = 13.8741(13),
for 3), whereas complex crystallizes in monoclinic space group, P2
a = 7.5765(2), b = 19.6005(6), c = 14.5861(4) and b = 102.679(1)° (for 2). The weak forces like lone
pairÁ Á Á Á Á Á /anionÁ Á Á interactions lead to various supramolecular architectures.
Ó 2013 Elsevier Ltd. All rights reserved.
1
and
3
crystallize in triclinic space group, P1 with cell dimensions
a
= 94.299(7)°, b = 97.281(7)° and
= 65.524(6)°, b = 73.373(6)° and
/c with cell dimensions
c
= 116.007(6)° (for
1
(
a
c
= 63.857(5)°
2
1
p
/
p
p
p
1
. Introduction
Copper(II) with d9 electronic configuration likes to undergo
Jahn–Teller distortion, leading to an elongated octahedral or
square pyramidal or square planar coordination. Strong-field li-
gands tend to coordinate to the four equatorial sites, leaving the
two axial sites vacant. When one of the four coordination sites of
the square plane of the metal ion is occupied by a strongly coordi-
nating anion, the tridentate mono-Schiff base is stabilized through
coordination to the three remaining sites. With weakly coordinat-
ing counter anions, however, it was shown that the mono-
condensed tridentate Schiff base underwent hydrolytic cleavage
to yield two bidentate strong-field chelating ligands which can oc-
cupy the four equatorial sites in order to fulfill the requirement of
having strong field ligand in all four equatorial sites of copper(II)
[16]. Very recently, our group has reported the copper(II) tem-
plated synthesis of mono- or di-condensed Schiff bases starting
from 1,2-diaminoethane and 3-methoxysalicyaldehyde where the
mono-condensed Schiff base is trapped as its copper(II) complex
in the presence of azide or pyridine [17]. However, in the absence
of the strongly coordinating azide/pyridine, the tridentate Schiff
Simple one-step reaction of various primary diamines, such as
,2-diaminoethane, 1,3-diaminopropane, o-phenylenediamine etc
1
with salicylaldehyde or its derivatives in 1:2 ratio yields the
well-known Salen-type tetradentate Schiff bases, which form very
stable mono- and poly-nuclear complexes with many transition
metals [1–7], with countless applications as materials [8,9], cata-
lysts [10–12] etc. The 1:1 condensation of a diamine with salicyal-
dehyde (or its derivative) may also be obtained in a good yield to
produce a ‘half unit’ by a template synthesis in the presence of me-
tal ions [13]. A templating agent may be defined as a species which
contains the essential information to arrange a set of building
blocks so that they can be connected in a specific way [14]. The
metal ion templated synthesis of the mono-condensed, tridentate
ligand having NNO donor set has also been reported by several
groups and the ligands have widely been used for the synthesis
of homo- and hetero-polynuclear complexes [15].
2 4
base undergoes rearrangement to form a N O donor Schiff
base. In order to stop this rearrangement, we have started with
N,N-diethyl-1,2-diaminoethane to prepare the tridentate Schiff
⇑
Corresponding author. Tel.: +91 9903756480.
E-mail address: shouvik.chem@gmail.com (S. Chattopadhyay).
0
277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.06.007

1
80
P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
base. This Schiff base is made to react with copper(II) in presence
or in absence of strongly coordinating cyanate. In presence of cya-
nate, double end-on cyanate bridged copper(II) complex is pro-
duced, but in absence of cyanate, amine nitrogen of the Schiff
base is protonated with the concomitant conversion of a potential
tridentate Schiff base into a bidentate ligand. Addition of base
stops the protonation and copper(II) complex with tridentate Schiff
base can be obtained from DMF solution. The fourth coordination
site is occupied by a DMF molecule. Herein, we would like to report
the variation of structures and geometries of copper(II) complexes
with the variation in the coordinating ability of the counter anion/
solvent.
2.2. Preparation
2.2.1. Preparation of 2-[(2-diethylamino-ethylimino)-methyl]-4-nitro-
phenol (HL)
A clear yellow solution of ligand, HL was synthesized by reflux-
ing
a methanol solution of 5-nitrosalicylaldehyde (170 mg,
1 mmol) with N,N-diethyl-1,2-diaminoethane (0.1 ml, 1 mmol) in
1:1 ratio for 2 h. It was not isolated and used directly for the prep-
aration of complexes 1, 2 and 3.
2.2.2. Preparation of [Cu(H
2
L)
2
(ClO
4
)]ClO
4
ÁH
2
O (1)
A methanol solution of Cu(ClO
4
)
2
Á6H
2
O (185 mg, 0.5 mmol) was
It is worth mentioning that supramolecular systems based on
coordination compounds have already received much interest be-
cause of their potential use as sensors, probes, photonic devices,
added into the methanol solution of the ligand HL (1 mmol) and re-
fluxed for 1 h to give a deep green solution. It was then cooled to
room temperature. An immediate separation of a small amount
of side product was filtered off. Single crystals, suitable for X-ray
diffraction, were obtained after few days by slow evaporation of
the filtrate in open atmosphere.
and catalysts and in host–guest chemistry [18–23]. Lone pairÁ Á Á
C–HÁ Á Á and anionÁ Á Á interactions are very common and well ac-
cepted among supramolecular chemists and are linked with the
p,
p
p
stabilization of molecules in the solid state [24,25]. AnionÁ Á Á
p
2 6
Yield: 585 mg (72%). Anal. Calc. for C26H40Cl CuN O15: C, 38.50;
interactions were primarily thought to be improbable due to the
H, 4.97; N, 10.36. Found: C, 38.4; H, 4.8; N, 10.2%. IR (KBr,
electron-donating character of anions and the expected repulsive
À1
cm ):1627 (
m
C@N), 1100 (
m
ClO4), 1315 (
m
NO2
À1
)
,
3451 (
mOH), UV–Vis,
interactions with aromatic
p
-systems. In the recent years, crystal-
interac-
3
À1
k
max
(nm)
max
(e ,
(dm mol cm ))
(acetonitrile) = 590
lographic as well as theoretical evidences for anionÁ Á Á
p
2
4
4
(
2.3 Â 10 ), 357 (1.8 Â 10 ), 251 (2.3 Â 10 ). Magnetic moment:
tions are increasingly reported. In the present paper, we report
the synthesis, characterization, X-ray crystal structures and supra-
molecular assembly of the molecular building blocks via lone
1
.72 BM.
pairÁ Á Á
p
,
p
Á Á Á
p
and anionÁ Á Á
p interactions in three new complexes
2
4
.2.3. Preparation of [Cu(L)DMF]ClO (2)
Methanol solution (25 ml) containing Cu(ClO
of copper(II).
4
)
2 2
Á6H O
(
370.5 mg, 1 mmol) was added to the yellow solution (25 ml) of
the ligand, HL (1 mmol) and refluxed for 1 h to obtain a deep green
solution. 10 drops of triethyl amine was added to it and stirred for
2
. Experimental
.1. Materials
All reagents were commercially available, reagent grade and
1
h. It was then kept at room temperature to get deep green com-
2
pound. Single crystals suitable for X-ray diffraction, were obtained
from the DMF solution on slow evaporation in open atmosphere
after few weeks.
were used without further purification.
Yield: 290 mg (58%). Anal. Calc. for C16
5.04; N, 11.20. Found: C, 38.2; H, 5.1; N, 11.1%. IR (KBr, cm ):
H
25ClCuN
4
O
8
: C, 38.4; H,
À1
Caution!!! Although no problems were encountered in this
work, perchlorate salts containing organic ligands are potentially
explosive. Only a small amount of the material should be prepared
and it should be handled with care.
1644 (
m
C@N), 1100 (
m
ClO4), 1313 (
m
NO2), UV–Vis, kmax (nm) (
e
max
4
,
3
À1
À1
2
(dm mol cm )) (acetonitrile) = 608 (1.6 Â 10 ), 357 (2.7 Â 10 ),
4
252 (2.7 Â 10 ). Magnetic moment: 1.73 BM.
Table 1
Crystal data and refinement details of complexes 1–3.
1
2
3
Formula
Formula weight
T (K)
C
26
H
40Cl
2
CuN
6
O
15
C
16
H
4
25ClCuN O
8
C
28 2 8 8
H36Cu N O
811.08
100(2)
500.4
293
739.75
100(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1ꢀ
monoclinic
triclinic
P1ꢀ
11.6149(8)
11.8145(9)
13.8741(13)
65.524(6)
73.373(6)
63.857(5)
2
1
P2 /c
11.3479(10)
12.5198(9)
13.6640(12)
94.299(7)
97.281(7)
116.007(6)
2
1.573
0.872
842
7.5765(2)
19.6005(6)
14.5861(4)
90
102.679(1)
90
a
(°)
b (°)
c
(°)
Z
D
l
4
À3
calc (g cm
)
1.573
1.211
1036
1.592
1.442
764
À1
(mm
)
F(000)
Total reflections
Unique reflections
Observed data [I > 2
12731
6309
2821
492
34654
6172
4457
37315
37315
28184
420
r
(I)]
Number of parameters
275
R
R
R
int
0.078
0.1181, 0.0879
0.0442, 0.0748
0.029
0.0583, 0.1188
0.0394, 0.1096
0.000
0.0603, 0.1109
0.0445, 0.1060
1
, wR
, wR
2
2
(all data)
[I > 2 (I)]
1
r

P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
181
À1
2
.2.4. Preparation of [Cu
Methanol solution (25 ml) containing Cu(OAc)
mmol) was added to a methanol solution (25 ml) of the ligand,
2
L
2
(NCO)
2
] (3)
analyzer. Infrared spectra in KBr (4500–500 cm ) were recorded
using a Perkin–Elmer RXI FT-IR spectrophotometer. Electronic
spectra in acetonitrile (900–200 nm) were recorded on a Jasco
V-630 UV–Vis spectrophotometer. Fluorescence spectra were ob-
tained on HORIBA Jobin Yvon Fluoro Max-P spectrophotometer at
room temperature. The magnetic susceptibility measurements
were done with an EG & PAR vibrating sample magnetometer,
model 155 at room temperature and diamagnetic corrections were
made using Pascal’s constants.
2
ÁH
2
O (199.6 mg,
1
HL (1 mmol) and refluxed for 1 h to give a deep green solution.
Aqueous solution of NaOCN (65 mg, 1 mmol) was added to it and
refluxed again for an additional hour to obtain deep green precip-
itate. The precipitate was separated from the solution by filtration
and dissolved in DMSO. Single crystals, suitable for X-ray diffrac-
tion, were obtained on slow evaporation of the DMSO solution in
open atmosphere after several weeks.
Yield: 390 mg (53%). Anal. Calc. for C28
.91; N, 15.15. Found: C, 45.3; H, 4.8; N, 15.2%. IR (KBr, cm ):
H
36Cu
2
N
8
O
8
: C, 45.46; H,
À1
4
2.4. X-ray crystallography
1
635 (
m
C@N), 1318 (
t
NO2), 2212 (
m
NCO), UV–Vis, kmax (nm) (
e
max
4
,
3
À1
À1
2
(
dm mol cm )) (acetonitrile) = 620 (3.6 Â 10 ), 362 (4.5 Â 10 ),
Single crystals of 1 and 3 of suitable dimensions were mounted
in inert oil and transferred to the cold gas stream of the cooling de-
vice. Data were collected at 100 K on a STOE IPDS 2T diffractometer
4
2
51 (4.6 Â 10 ). Magnetic moment: 1.71 BM.
2.3. Physical measurements
using graphite monochromated Mo Ka radiation, and were cor-
rected for absorption effects using multiscanned reflections. Non
hydrogen atoms were refined anisotropically. H atoms of the water
molecule were located by difference Fourier maps and were kept
Elemental analysis (carbon, hydrogen and nitrogen) of the com-
plexes were performed on
a Perkin–Elmer 240C elemental
Scheme 1. Formation of 1, 2, 3 and some related complexes.

1
82
P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
fixed. All other hydrogen atoms were placed in their geometrically
idealized positions and constrained to ride on their parent atoms.
Programs used: SHELXL-97 [26,27], PLATON [28], XAREA [29], SIR92
perchlorate compared to copper(II) acetate may be the reason for
this difference. The nitro group, present in the ligand moiety, has
already increased the acidity of the phenolic hydrogen atom and
the ligand is expected to exist as a zwitterion. Addition of cop-
per(II) acetate can easily deprotonate the ligand mainly because
the acetate tends to remain as the acetic acid abstracting proton
from the Schiff base. On the other hand, perchloric acid is a strong
acid and thus the addition of copper(II) perchlorate could not
deprotonate the ligand, in absence of a base. However, the addition
of triethylamine abstracts the proton from the zwitterionic Schiff
base to form complex 2 in DMF solution. Complex 2 is square pla-
nar in which the three coordination sites of copper(II) are occupied
by the tridentate Schiff base and the fourth coordination site is
occupied by the strongly coordinating DMF molecule. Addition of
NaOCN into the methanol solution of complex 2 produces complex
[
30], DIAMOND [31], ORTEP [32] and MERCURY [33]. In 1, two carbon
atoms, C(11) and C(13), were disordered and two sets of positions
were refined for both with occupancies of x and 1Àx with x = 0.342
and 0.364, respectively. All the H atoms, attached with C(12) and
C(13), were also disordered and two sets of positions were refined
for all of them with occupancies of x and 1Àx, with x converging to
0
.364. Similarly, all H atoms, attached with C(10) and C(11), were
also disordered and two sets of hydrogen atoms were refined with
occupancies of x and 1Àx with x = 0.342.
Single crystal of complex 2 having suitable dimensions was
used for data collection by means of a ‘Bruker SMART APEX II’ diffrac-
to-meter equipped with graphite-monochromated Mo K
a radia-
tion (k = 0.71073 Å) at 293 K. The structure was solved by direct
methods and refined by full-matrix least squares on F , using the
3. Addition of NaN
plex 2 produces [Cu
3
or NH
(N
4
SCN to the methanol solution of com-
)2] or [Cu (NCS) ] respectively. The
2
2
L
2
3
2
L
2
2
SHELX-97 package [27]. Non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms were placed in
their geometrically idealized positions and constrained to ride on
the atoms to which they are attached. Empirical absorption correc-
tions were carried out with the ABSPACK program [34]. The crystallo-
graphic and refinement data are summarized in Table 1.
greater coordinating ability of the pseudo-halides may be the driv-
ing force for the replacement reaction. The formations of all the
complexes are shown in Scheme 1.
3.2. Description of the structures
3
.2.1. [Cu(HL)
2
(ClO
4
)]ClO
4
ÁH
2
O (1)
Complex 1 crystallizes as green blocks in triclinic space group
ꢀ
3
. Results and discussion
P1. The perspective drawing of the copper(II) complex is shown
in Fig 1. The asymmetric unit consists of a [Cu(HL) ClO ] cation,
2 4
+
3
.1. Synthesis of copper(II) complexes
one perchlorate anion and a water of crystallization. The copper(II)
is five coordinated with (4 + 1) square pyramidal (NNOO and O)
geometry. The distortion of the coordination polyhedron from
the square pyramid to the trigonal bipyramid is calculated by the
The tridentate Schiff-base ligand (HL) was prepared by the con-
densation of N,N-diethyl-1,2-diaminoethane and with 5-nitrosali-
cylaldehyde in 1:1 molar ratio, following the literature method
Addison parameter (
The value of is defined as the difference between the two largest
donor–metal–donor angles divided by 60, a value that is 0 for the
ideal square pyramid and 1 for the trigonal bipyramid. The value
s) [38] as an index of the degree of trigonality.
[
35]. Addition of copper(II) acetate into the methanol solution of
the ligand produces [CuL(OAc)], the structure of which is already
reported by a different group [36]. Addition of NaN or NH SCN
produces [Cu (N ] or [Cu (NCS) ] respectively [37]. Use of
s
3
4
s
2
L
2
3
)
2
2
L
2
2
is 0.15 in complex 1, which indicates that the coordination geom-
etry is only slightly distorted from square-pyramidal structure to-
wards trigonal bi-pyramidal one. The four coordinating atoms
making up the basal plane are two phenoxo O atoms {O(1) and
O(4)} and two imine N atoms {N(1) and N(4)}} from two proton-
ated Schiff bases, while the apical site is occupied by one oxygen
atom {O(7)} of a perchlorate. Deviations of the coordinating atoms,
NaOCN produces complex 3. Interestingly, addition of copper(II)
perchlorate could not produce any complex of the formula [CuL(X)]
[
where X may be perchlorate or water or methanol present in the
+
2 4
medium], rather [Cu(HL) (ClO )] (1) is formed, where the amine N
of the tridentate Schiff base ligand is protonated and the denticity
of the ligand is reduced to two. The more acidity of the copper(II)
Fig. 1. Perspective view of complex 1. Only the relevant atoms are labeled. Water molecule and perchlorate anion are not shown for clarity.

P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
183
Table 2
Selected bond lengths of complexes 1, 2 and 3.
1
2
3
Cu(1)–O(1)
Cu(1)–O(2)
Cu(1)–O(4)
Cu(1)–O(7)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(4)
Cu(1)–N(4)#
Cu(2)–N(102)
Cu(2)–O(101)
Cu(2)–N(101)
Cu(2)–N(104)
1.892(3)
–
1.917(3)
2.536(5)
2.003(4)
–
1.999(4)
–
–
–
–
–
1.8908(14)
1.9601(16)
–
–
1.9279(16)
2.0549(17)
–
–
–
–
–
–
1.9324(12)
–
–
–
2.0861(15)
1.9467(13)
1.9374(14)
2.7248(14)
1.9412(12)
1.9284(12)
2.0512(15)
1.9388(14)
Symmetry element, # = Àx, 1 À y, Àz.
O(1), O(4), N(1) and N(4) from the least-square mean plane
through them are 0.082(4), 0.081(4), -0.081(5) and -0.082(4) Å
respectively. This deviation from planarity of the equatorial plane
is also manifesting itself in the trans angles {O(1)–Cu(1)–O(4),
N(1)–Cu(1)–N(4)} which are 179.46(15) and 170.38(18). As is
usual for square pyramid structure, the copper(II) is displaced
0
.086(7) Å from the basal plane towards the apically coordinated
oxygen, O(7). The distance between copper(II) and apical oxygen
atom, O(7) {Cu(1)–O(7), 2.536(5) Å} is significantly longer than
the basal bonds {Cu–Obasal, 1.892–1.917 Å}, thus, suggesting the
presence of a Jahn–Teller effect. In the basal plane, the Cu–Nimine
distances fall in the range 1.999–2.003 Å, which is also observed
in similar systems [39,40]. The different angles around the copper
atom in the equatorial plane is ꢀ359.95°. Selected bond lengths are
summarized in Table 2. Selected bond angles are given in Table S1.
The closest conformation of six-membered chelate ring, R1
{R1 = Cu(1)–O(1)–C(7)–C(2)–C(1)–N(1)} is twist-boat with pucker-
ing parameters [39] q = 0.086(4) Å, h = 100(3)° and / = 210(3)°
whereas that of other ring, R2 {R2 = Cu(1)–O(4)–C(20)–C(15)–
C(14)–N(4)}, is screw-boat with puckering parameters
q = 0.130(3) Å, h = 64.5(18)° and / = 32(2)° [41].
Fig. 2. H bonding network in complex 1. Only the relevant H atoms are shown.
Symmetry code = 2 À x, Ày, 2 À z.
H(5A), attached with N(5), of the Schiff base forms strong H
bond with O(14) of the ionic perchlorate. On the other hand,
H(2), attached with amine nitrogen, N(2), is involved in hydrogen
bonding with O(100) of a water molecule present in the crystal.
One hydrogen atom of the same water molecule, H(10E), forms a
H-bond with an oxygen atom, O(8) of a coordinated perchlorate.
The other hydrogen of the water molecule, H(10F) forms H-bond
⁄
Table 3
Hydrogen bond distances (Å) and angles (°) of complex 1.
D–HÁ Á ÁA
D–H
DÁ Á ÁA
HÁ Á ÁA
\D–HÁ Á ÁA
⁄
⁄
N(2)–H(2)Á Á ÁO(100)
N(5)–H(5A)Á Á ÁO(14)
O(100)–H(10E)Á Á ÁO(8)
0.79(4)
0.88(5)
0.87(6)
0.88(6)
2.797(6)
2.842(6)
2.860(7)
3.009(7)
2.03(4)
1.96(5)
2.08(7)
2.16(6)
163(5)
178(8)
149(6)
163(7)
with O(9) of a symmetry related ( = 2 À x, Ày, 2 À z) coordinated
perchlorate. Thus a H-bonded dimer is formed (Fig. 2). The details
of H-bonding are given in Table 3.
⁄
O(100)–H(10F)Á Á ÁO(9)
The non-coordinating atom, O(8) makes a
Fig 3) with the chelate ring, R1 (Table 4). This chelating ring fur-
ther undergoes strong face-to-face (Table 5) stacks with an
pÁ Á Áanion interaction
⁄
D, donor; A, acceptor; H, hydrogen; symmetry element = 2 À x, Ày, 2 À z.
(
pÁ Á Áp
identical chelating ring, R1 and a phenyl ring, R3 {R3 = C(2)/C(3)/
The molecular structure of complex 2 consists of a [Cu(L)(DMF)]+
C(4)/C(5)/C(6)/C(7)} of a neighbouring molecule of symmetry,
cation and one perchlorate anion. The structure determination re-
1
À x, Ày, 2 À z. The non-coordinating atom, O(2) makes a lone
pairÁ Á Á contact with the phenyl ring, R4 {R4 = C(15)/C(16)/C(17)/
C(18)/C(19)/C(20)} of the same symmetry. Three more inter-
À
veals that the tridentate deprotonated Schiff base ligand, L coor-
p
dinates to the copper atom, Cu(1) via the phenolate oxygen
atom, O(1), imine nitrogen atom, N(1) and the amine nitrogen
atom, N(2) forming one five and one six membered chelate rings.
The DMF oxygen atom, O(2) occupies the fourth coordination site
forming a slightly distorted square-planar geometry around the
metal center. The deviations of the coordinating atoms, O(1),
O(2), N(1) and N(2) from the least-square mean plane through
them are À0.011(1), 0.011(2), 0.011(2) and À0.011(2) Å respec-
tively. This deviation from planarity of the equatorial plane is also
manifesting itself in the trans angles {O(1)–Cu(1)–N(2), O(2)–
Cu(1)–N(1)} which are 177.79(7) and 176.15(7). The deviation of
the copper(II) ion from the said equatorial plane is -0.041(2) Å.
The Cu–Nimine distance {1.9279(16) Å} is shorter than the
pÁ Á Áp
actions are also formed in complex 1. Firstly the chelating ring, R2
is stacked over the phenyl ring, R3 of the symmetry related neigh-
bouring molecule. Secondly the phenyl ring, R3 is stacked over the
chelate rings, R2 {R2 = Cu(1)/O(4)/C(20)/C(15)/C(14)/N(4)} and R1
of the same neighbouring molecule of symmetry, 1 À x, Ày, 2 À z.
Thus a supramlecular dimer is formed via lone pairÁ Á Á
p,
p
Á Á Á
p
and
p
Á Á Áanion interactions (Fig 3).
3.2.2. [Cu(L)DMF]ClO
4
(2)
Complex 2 crystallizes in the monoclinic space group P2
1
/c.
The perspective view of the copper(II) complex is shown in Fig 4.

1
84
P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
Fig. 3. Supra-molecular dimer produced by the lone pairÁ Á Áp (blue), pÁ Á Áp (pink) and pÁ Á Áanion (green) interactions in complex 1. (Colour online.)
Table 4
Geometrical parameters (Å, °) for the lone pairÁ Á Á
p/anionÁ Á Á
p
interactions for the complexes 1–3.
XÁ Á ÁCg(J)
Complex
YÀXÁ Á ÁCg(J)
YÁ Á ÁCg(J)
\YÀXÁ Á ÁCg(J)
XÀPerp
1
N(3)–O(2)Á Á ÁCg(4)
3.225(4)
2.995(5)
3.496(3)
3.713(4)
3.520(2)
3.312(2)
3.7505(14)
3.5723(15)
3.4442(16)
3.354(5)
3.775(2)
85.1(3)
3.171
2.995
3.355
3.332
3.143
2.976
3.418
3.393
3.380
Cl(1)–O(8)Á Á ÁCg(1)
Cl–O(4)Á Á ÁCg(2)
Cl–O(4)Á Á ÁCg(3)
Cl–O(5)Á Á ÁCg(2)
Cl–O(6)Á Á ÁCg(2)
N(3)–O(2)Á Á ÁCg(3)
112.9(3)
84.92(13)
123.73(17)
83.84(9)
92.11(11)
66.36(9)
100.78(10)
79.80(10)
2
3
3.6504(10)
4.6417(11)
3.6504(10)
3.6504(10)
3.4465(16)
3.9902(17)
3.4465(16)
#
#
N(3) –O(2) Á Á ÁCg(8)
N(3)–O(3)Á Á ÁCg(3)
For complex 1, Cg(1) = centroid of ring [Cu(1)–O(1)–C(7)–C(2)–C(1)–N(1)] and Cg(4) = centroid of ring [C(15)–C(16)–C(17)–C(18)–C(19)–C(20)]; for complex 2,
Cg(2) = centroid of ring [Cu(1)–O(1)–C(1)–C(6)–C(7)–N(1)] and Cg(3) = centroid of ring [C(1)–C(2)–C(3)–C(4)–C(5)–C(6)] and for complex 3, Cg(3) = centroid of ring [Cu(1)–
O(1)–C(3)–C(2)–C(1)–N(2)] and Cg(8) = centroid of ring [C(102)–C(103)–C(104)–C(105)–C(106)–C(107)]. XÀPerp = perpendicular distance between X and the ring J (Å).
Symmetry element, # = Àx, 1 À y, Àz.
Table 5
Geometrical parameters (Å, °) for the
p
-stacking moieties involved in the
Rca
pÁ Á Áp interactions for the complexes 1-3.
Complex
Rings IÀJ
R1vb
R2vc
a
b
c
1
Cg(1)–Cg(1)
Cg(1)–Cg(3)
Cg(2)–Cg(3)
Cg(2)–Cg(3)
Cg(3)–Cg(3)
Cg(4)–Cg(4)
Cg(8)–Cg(8)
3.522(3)
4.024(3)
3.693(3)
3.8930(12)
3.4070(13)
3.6343(10)
3.7528(10)
3.3893(18)
3.3624(18)
3.3379(18)
3.2969(7)
3.3533(9)
3.3842(6)
3.4728(6)
3.3893(18)
3.457(2)
3.504(2)
3.3674(9)
3.3534(9)
3.3842(6)
3.4728(6)
0
15.77
30.80
18.43
30.12
10.18
21.38
22.27
15.77
33.33
25.34
32.12
10.18
21.38
22.27
2.7(2)
8.7(2)
2.18(9)
0
0
0
2
3
a
b
c
Distance between the centroids of ring I and ring J.
Perpendicular distance from the centroid of ring I to ring J.
Perpendicular distance from the centroid of ring J to ring I.
a = Dihedral angle between ring I and ring J(°); b = angle Cg(I)–Cg(J) vector and normal to plane I (°); c = Angle
Cg(I)–Cg(J) vector and normal to plane J (°). For complex 1, Cg(1) = centroid of ring [Cu(1)–O(1)–C(7)–C(2)–C(1)–N(1)]; Cg(2) = centroid of ring [Cu(1)–O(4)–C(20)–C(15)–
C(14)–N(4)] and Cg(3) = centroid of ring [C(2)–C(3)–C(4)–C(5)–C(6)–C(7)]; for complex 2, Cg(2) = centroid of ring [Cu(1)–O(1)–C(1)–C(6)–C(7)–N(1)] and Cg(3) = centroid of
ring [C(1)–C(2)–C(3)–C(4)–C(5)–C(6)] and for complex 3, Cg(4) = centroid of ring [C(2)–C(3)–C(4)–C(5)–C(6)–C(7)] and Cg(8) = centroid of ring [C(102)–C(103)–C(104)–
C(105)–C(106)–C(107)].
Cu–Namine {2.0549(17) Å} distance as were observed in similar sys-
tems [39,40]. Sum of the different angles around the copper(II) is
q(2) = 0.417(2) Å and /(2) = 291.7(2)° [41]. There is no H-bond
present in complex 2.
ꢀ
359.9°. Selected bond lengths are summarized in Table 2. Se-
lected bond angles are given in Table S2. The closest conformation
The non coordinating atoms O(4), O(5) and O(6) of a dangling
perchlorate anion are orientated towards the
chelate ring R2 {Cu(1)/O(1)/C(1)/C(6)/C(7)/N(1)} in such an angle
that it leads to three significant anionÁ Á Á interactions (Table 4).
p-face (Fig 5) of the
of the five-membered chelate ring, R1 {R1 = Cu(1)–N(1)–C(8)–
C(9)–N(2)}
is
envelope
with
puckering
parameters
p

P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
185
Fig. 4. Perspective view of complex 2. Only the relevant atoms are labeled. Perchlorate anion is not shown for clarity.
of the tridentate Schiff base ligand and a nitrogen atom, N(4), of
the end-on bridged cyanate; this defines the basal plane. A second
#
nitrogen atom, N(4) (Symmetry code: # = Àx, 1 À y, Àz), from the
centrosymmetrically related bridging cyanate coordinates axially
at a rather long distance furnishing an elongated square-pyramidal
(
4 + 1) geometry for each copper(II) center (Fig 6). The addison
parameter (
s
) is ꢀ0.157. As usual for a square pyramid structure,
the copper atom for each model is slightly pulled out of the mean
squares plane towards the apical donor atom at a distance
-
0.075(2) Å. The intra-chain CuÁ Á ÁCu distances are 3.517 Å. The
closest conformation of the five-membered chelate ring {Cu(1)–
N(1)–C(9)–C(8)–N(2)} is envelope with puckering parameters
q(2) = 0.4851(15) Å; /(2) = 43.65(18)° [41]. Selected bond lengths
are summarized in Table 2. Selected bond angles are given in
Table S3. The bridging Cu
planar as dictated by the symmetry. Due to the formation of basal–
apical 1,1-NCO bridging, the bridging Cu–N bond lengths are sig-
nificantly different ( d = 0.7874 Å). The bridging NCO anions are
quasi-linear; the N@C@O angle is 177.84°. Similarly the coordinat-
ing NCO anion in case of A is also quasi-linear; the N@C@O angle is
2 2
N network in both the dimer is exactly
l
D
Fig. 5.
p
Á Á Áp
(pink) and
pÁ Á Áanion (green) interactions in complex 2. (Colour online.)
1
77.01°. There is no H-bonded network in complex 3.
The non-coordinating atoms O(2) and O(3) are orientated toward
In addition, the position of O(4) is such that it’s good enough to
interaction by interacting with phenyl
ring R3 {R3 = C(1)/C(2)/C(3)/C(4)/C(5)/C(6)} of same symmetry. It
the
N(2) of symmetry, 1 À x, Ày, Àz} in such an angle that it leads to
two significant lone pairÁÁÁ interactions (Table 4). An additional
interaction is resulted due to the orientation of O(2)
symmetry code, # = Àx, 1 À y, Àz} over the phenyl ring, R8
R8 = C(102)/C(103)/C(104)/C(105)/C(106)/C(107)}. There are also
interactions (Table 5). Firstly the phenyl ring,
p-face of the chelate ring, R3 {R(3) = Cu(1)/O(1)/C(3)/C(2)/C(1)/
give rise another anionÁ Á Á
p
p
has also been observed that three additional strong face-to-face
#
lone pairÁ Á Á
p
p p stacks (Table 5) leads to the formation of a dimeric unit. R3
Á Á Á
{
{
stacks with an identical phenyl ring, R3 and a chelate ring, R2 of
a neighbouring molecule of symmetry, 2 À x, 2 À y, Àz. The third
two important
pÁ Á Áp
p
2
Á Á Á
p
stack occur between R2 and R3 {symmetry code: 2 À x,
R4 {R4 = C(2)/C(3)/C(4)/C(5)/C(6)/C(7)} is stacked over another phe-
nyl ring, R4 of the neighbouring molecule of symmetry, 1 À x, Ày, Àz.
Similarly the phenyl ring, R8 is stacked over another identical phenyl
ring, R8 of the neighbouring molecule of symmetry code: 1 À x,
À y, Àz}.
3
.2.3. [Cu
2 2 2
L (NCO) ] (3)
ꢀ
Complex 3 crystallizes in the triclinic space group P1. The struc-
1
À y, 1 À z. All the supramolecular interactions are shown in Fig 7.
ture determination reveals that the asymmetric unit consists of
two crystallographically independent centrosymmetric dimers
(
A and B). In the dimer, two distorted square-pyramidal copper(II)
3.3. IR, electronic spectra, magnetic moments and luminescence
studies
centers are bridged by the two centrosymmetrically related cya-
nate ions in basal–apical, end-on fashion. Within the dimeric units
each of the two trigonally distorted square-pyramidal copper(II)
centers is coordinated equatorially by one amine nitrogen atom,
N(1), one imine nitrogen atom, N(2) and one oxygen atom O(1),
The IR bands corresponding to the C@N stretching vibrations
À1
for complexes 1–3 appear in the range 1627–1644 cm [42]. A
À1
broad band at around 1100 cm in the IR spectrum of complex

1
86
P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
Fig. 6. Perspective view of complex 3. Symmetry code, # = Àx, 1 À y, Àz.
Fig. 7. Lone pairÁ Á Á
p
(blue) and
pÁ Á Á
p
(pink) interactions in complex 3. Symmetry code, # = Àx, 1 À y, Àz. (Colour online.)
1
indicates the presence of perchlorate anion [43]. An intense band
4. Conclusion
À1
within 1310–1319 cm may be attributed to
t
NO2 vibration in the
IR spectra of all the complexes [35]. Interestingly in the IR spec-
Three new copper(II) complexes have been isolated and char-
acterized by physico-chemical and structural studies. The aim of
the work was to prepare copper(II) complexes with a Schiff base
ligand involving N,N-diethyl-1,2-diaminoethane and 5-nitrosali-
cyaldehyde. The presence of nitro group in the 5 position of
the phenyl ring increases the acidity of the phenolic OH and
the Schiff base is expected to exist in its zwiterionic form. This
zwitterionic ligand can be trapped as a copper(II) complex on
adding copper(II) perchlorate to the methanol solution of the li-
gand. X-ray diffraction study has confirmed the presence of zwit-
terionic ligand in the complex. Addition of a suitable base may
deprotonate the Schiff base making it a tridentate one. This tri-
dentate Schiff base may also be trapped as a square planar cop-
per(II) complex and suitable crystals may be grown from DMF
solution. X-ray diffraction shows that the fourth coordination
site of copper(II) is occupied by the solvent DMF molecule.
Replacement of DMF can be done by the addition of more nucle-
ophilic cyanate, azide or thiocyanate. Complexes containing
zwitterionic Schiff base are not very common in literature. Thus
it opens up new possibilities for the synthesis of complexes hav-
ing zwitterionic Schiff bases.
À1
trum of complex 1, a broad band at ꢀ3430 cm is observed may
be assigned to OH stretching vibration. The IR specta of 3 shows
À1
the most intense absorption band at
to the NCO ligand [44].
m
as 2212 cm corresponding
The electronic spectra in acetonitrile are recorded in the range
00–1000 nm. The intense absorption bands at short wavelengths,
2
around 360 nm, may be assigned to ligand to metal ion charge
transfer bands (LMCT). The absorptions around 600 nm may be as-
signed to d–d transitions.
Room temperature magnetic susceptibility measurements for
the complexes1 and 2 show that they have magnetic momentvalues
in the range 1.71–1.72 BM, as expected for discrete magnetically
non-coupled spin only value for copper(II) ion, as also observed in
similar systems [45–47]. The room temperature magnetic moment
of complex 3 is also very close to 1.73 BM and this suggests that
no copper-copper interactions at room temperature are present in it.
The complexes 1–3 exhibit luminescence in acetonitrile med-
ium. On excitation at 350 nm, emissions observed at 426, 425
and 424 nm respectively for complexes 1, 2 and 3. These are as-
1
⁄
signed as intra-ligand (p–p ) fluorescence [48].

P.K. Bhaumik et al. / Polyhedron 62 (2013) 179–187
187
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This work was supported by the DST, India, under FAST Track
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are thankful to Mr. Ramesh Chandra Santra and Dr. Saurabh Das,
Department of Chemistry, Jadavpur University, India for providing
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