Complexes of NiX2 (X = Cl- and NO3 -) with a NNO donor Schiff base: Anion dependent structural variations and spectroscopic behaviour

Article abstract of DOI:10.1016/j.poly.2011.12.014

Two new nickel(II) complexes, [NiL(H₂O)₂Cl] (1) and [{NiLL′(H₂O)}₂(μ-H)]NO₃·H ₂O (2), have been synthesized using a tridentate Schiff base ligand, HL, 2-[(2-dimethylamino-ethylimino)-methyl

Full text of DOI:10.1016/j.poly.2011.12.014

Polyhedron 34 (2012) 67–73
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Polyhedron
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ꢀ
ꢀ
Complexes of NiX (X = Cl and NO ) with a NNO donor Schiff base: Anion
2
3
dependent structural variations and spectroscopic behaviour
a,b
a
c
a,
⇑
Subrata Naiya , Saptarshi Biswas , Michael G.B. Drew , Ashutosh Ghosh
a
Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India
Susil Kar College, Ghoshpur, Champahati, Baruipur, 24 Parganas(S), West Bengal 743330, India
School of Chemistry, The University of Reading, P.O. BOX 224, Whiteknights, Reading RG6 6AD, UK
b
c
a r t i c l e i n f o
a b s t r a c t
0
Article history:
Two new nickel(II) complexes, [NiL(H O) Cl] (1) and [{NiLL (H O)} (
l
-H)]NO ꢁH O (2), have been synthe-
2
2
2
2
3
2
Received 10 October 2011
Accepted 9 December 2011
Available online 23 December 2011
sized using a tridentate Schiff base ligand, HL, 2-[(2-dimethylamino-ethylimino)-methyl]-phenol, along
ꢀ
ꢀ
0
with Cl or NO
3
as an anionic co-ligand or counter anion (where L H = salicylaldehyde). Both complexes
have been characterized by X-ray crystallography. The structural analyses reveal that complex 1 is mono-
nuclear whereas 2 is a hydrogen-bridged dinuclear complex. The Ni(II) ions possess a distorted octahe-
dral geometry in both structures. Both complexes show negative solvatochromic behaviour with
increasing donor number (DN) of the solvent. In more coordinating solvents, like DMSO or methanol,
the colour of the solutions is green, whereas in less coordinating solvents, like dichloromethane (DCM)
or acetonitrile, it is red.
Keywords:
Nickel(II)
Schiff base
Solvatochromic behaviour
Hydrogen-bridged
Donor number (DN)
Ó 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
The Schiff base complexes of transition metals are one of the
differences in the crystal field stabilization energy (CFSE). For
example, the CFSE of ethylenediamine derived Schiff bases, which
usually form shorter Ni–N bonds, is higher than that of 1,3-pro-
panediamine derivatives [33–34]. As a consequence, most of the
complexes of the former ligand are square planar [28–32] whereas
those of the latter are octahedral or square pyramidal [33,34]. A
CSD search shows that there are only two complexes of Ni(II) with
ethylenediamine and salicylaldehyde derived Schiff bases in which
the coordination geometry around Ni(II) is not square planar [36].
In this regard, the selection of the anionic co-ligand should also be
very important as it also contributes to the aggregate CFSE. Inter-
estingly, in most of the reported complexes the anionic co-ligand
is strongly coordinating, being either an azide or a thiocyanate
[28–32].
most exhaustively studied topics in coordination chemistry be-
cause of the ease with which they can be synthesized, their versa-
tility and wide range of complexing abilities [1–6]. The literature
clearly shows that these complexes played an important role in
the development of modern coordination chemistry [2–6], and
are also found at key points in the development of inorganic bio-
chemistry [7], catalysis [8,9], magnetism [10–15], gas storage
[
16–18], medical imaging [19] and optical materials [20,21].
Although imines are labile and readily hydrolyzed, they are usually
stabilized in metal complexes. However, during complex forma-
tion, the Schiff base may undergo hydrolysis and it has been ob-
served that the hydrolysis is dependent on several factors, such
as the nature of the metal ions [22,23], the pH of the reaction med-
ium [24], the size of the chelate rings formed by the diamine frag-
ment of the Schiff base [25] and the coordinating ability of the
counter anions [26,27].
One of the interesting aspects of the chemistry of Ni(II) with tri-
dentate NNO donor Schiff base ligands is that a small variation in
the diamine and/or the carbonyl compound from which the Schiff
base is derived can bring about significant variations in the coordi-
nation geometry [28–34], which seem likely to be due to slight
We are therefore interested in synthesizing Ni(II) complexes of
such Schiff bases, along with some weakly coordinating anions. In
ꢀ
ꢀ
the present work, we use Cl and NO
two complexes [NiLCl(H O)
3
salts of Ni(II) to prepare
0
2
2
] (1) and [{NiLL (H
(2), where HL = 2-[(2-dimethylaminoethylimino)-methyl]-phenol
and L H = salicylaldehyde. Both complexes have been characterized
2
O)}
2
3 2
(l-H)]NO ꢁH O
0
by single crystal X-ray diffraction analysis. Complex 1 is a mono-
mer and 2 is a rare type of hydrogen bridged dimer, while in both
complexes Ni(II) has a six-coordinate distorted octahedral environ-
ment. The Schiff base ligand undergoes hydrolysis to form the
mixed ligand complex 2. The UV–Vis spectral behaviour of the
complexes in different solvents has also been studied as the colour
of the solutions is dependent on the coordinating ability of the
solvents.
⇑
Corresponding author. Tel.: +44 01223 762910; fax: +44 01223 336033.
E-mail address: ghosh_59@yahoo.com (A. Ghosh).
0
277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.12.014

6
8
S. Naiya et al. / Polyhedron 34 (2012) 67–73
Table 1
2
. Experimental
N,N-Dimethyl-1,2-ethanediamine and salicylaldehyde were
Crystal data and structure refinement of complexes 1 and 2.
1
2
purchased from Lancaster and were of reagent grade. They were
used without further purification.
Formula
M
Crystal system
Space group
a (Å)
C
11
H
19ClN
2
NiO
3
C
36 45 5 2 12
H N Ni O
321.44
orthorhombic
Pnma
8.7484(4)
7.6645(4)
20.8570(10)
1398.5(1)
296(2)
857.15
orthorhombic
Pna2
19.3255(7)
12.4540(4)
15.7547(6)
3791.8(2)
150(2)
4
1.505
1800
1.062
1792
1
2.1. Synthesis of the Schiff base ligand 2-[(2-
dimethylaminoethylimino)-methyl]-phenol (HL)
b (Å)
c (Å)
3
V (Å )
The tridentate Schiff base ligand was prepared by the condensa-
tion of salicylaldehyde (1.0 mL, 10 mmol) and N,N-dimethyle-
thane-1,2-diamine (1.1 mL, 10 mmol) in methanol (20 mL) under
reflux for 1 h. The resulting dark yellow solution was then used di-
rectly for complex formation.
T (K)
Z
4
ꢀ3
Dcalc (g cm
)
1.527
656
1.580
672
F(000)
l
(mmꢀ1)
F(000)
R
int
0.058
16651
2174
1948
1.207
0.0667, 0.2155
0.0717, 0.2178
0.070
2
.2. Synthesis of [NiL(H
2
O)
2
Cl] (1)
Total reflections
Unique reflections
I > 2
GoF
25806
10726
5606
0.731
0.0436, 0.0629
0.0951, 0.0688
r
(I)
NiCl
was added to a methanolic solution (ꢂ15 mL) of the ligand (HL)
5 mmol) with constant stirring. The colour of the solution turned
2 2
ꢁ6H O (1.188 g, 5 mmol), dissolved in 10 mL of methanol,
R
R
1
, wR
, wR
2
2
[I > 2
[all data]
r
(I)]
(
1
green. By slow evaporation of the resulting solution at room tem-
perature, grassy green X-ray quality, rectangular shaped single
crystals were obtained after 2 days.
the CCD. 321 frames were measured with a counting time of 10 s.
Data analysis was carried out with the CRYSALIS program [38]. Both
structures were solved using direct methods with the SHELXS97 pro-
gram [39]. The non-hydrogen atoms were refined with anisotropic
thermal parameters. The hydrogen atoms bonded to carbon were
included in geometric positions and given thermal parameters
equivalent to 1.2 times those of the atom to which they were at-
tached. In both structures, hydrogen atoms bonded to oxygen were
readily located in the difference Fourier maps and refined with dis-
tance constraints, the only exception being the hydrogen between
O(11A) and O(11B) in 2 (see later discussion). The structure of 1
was refined in the space group Pnma, with the majority of the
atoms on the mirror plane. However parts of the saturated ring
were refined with 50% occupancy either side of the mirror plane.
Yield: 1.20 g, 75%. Anal. Calc. for C11
2 3
H19ClN NiO (1): C, 41.10;
H, 5.96; N, 8.72. Found: C, 41.00; H, 5.99; N, 8.67%. IR (KBr pellet,
ꢀ
1
cm ): 3377 (broad) m(OH), 1635 m(C@N), kmax (methanol, nm):
5
87, 887.
l
eff = 2.99 B.M.
0
2
.3. Synthesis of [{NiLL (H
O)}
2 2
3 2
(l-H)]NO ꢁH O (2)
The procedure was the same as that used for complex 1 except
that a methanolic solution of Ni(NO O (1.455 g, 5 mmol) was
3
)
2
ꢁ6H
2
added to the ligand solution (5 mmol) instead of the nickel chloride
solution. The resulting deep green solution was left to stand over-
night in air to obtain block-shaped deep green X-ray quality single
crystals of complex 2.
Yield: 3.13 g, 73%. Anal. Calc. for C36
45 5 2
H N Ni O12 (2): C, 50.44;
An empirical absorption correction for 2 was carried out using
H, 5.29; N, 8.17; Found: C, 50.45; H, 5.33; N, 8.15%. IR (KBr pellet,
the ABSPACK program [40]. The structures were refined on F2 using
ꢀ
1
cm ): 3380 (broad)
m(OH), 1631 m(C@N), kmax (methanol, nm):
SHELXL97 [39].
5
95, 887. eff = 2.95 B.M.
l
2.4. Physical measurements
3
. Results and discussion
Elemental analyses (C, H and N) were performed using a Perkin-
Elmer 2400 series II CHN analyzer. IR spectra in KBr pellets (4500–
3
.1. Synthesis of the complexes
ꢀ1
5
00 cm ) were recorded using a Perkin-Elmer RXI FT-IR spectro-
The mono-condensed tridentate Schiff base ligand HL and its
photometer. Electronic spectra in methanol (1000–200 nm for
the complexes were recorded in a Hitachi U-3501 spectrophotom-
eter. Magnetic susceptibility measurements at 300 K were carried
out with a Sherwood Scientific Co., UK, magnetic susceptibility bal-
ance and diamagnetic corrections were made using Pascal’s con-
stants. Thermal analyses (TG-DTA) were carried out on a Mettler
Toledo TGA/SDTA 851 thermal analyzer in a dynamic atmosphere
hydroxo-bridged, methoxo-bridged and azido-bridged dinuclear
complexes obtained with the Fe(III) ion have been reported by us
recently [41,42]. In the present investigation we have used this li-
gand for the synthesis of Ni(II) complexes with anionic chloride
and nitrate co-ligands. Both complexes have been prepared in a
similar way: the tridentate ligand HL was allowed to react with
the respective Ni(II) salt in a 1:1 molar ratio in methanol medium
at ambient temperature. The structure and composition of the
resulting compounds are, however, very different. A mononuclear
3
ꢀ1
of dinitrogen (flow rate: 30 cm min ). The samples were heated
ꢀ1
in an alumina crucible at a rate of 10 °C min
.5. Crystal data collection and refinement
.
complex, [NiL(H
2
O)
2
Cl] (1) is produced when the anionic ligand
is allowed to react
2
is chloride (Scheme 1). However, when Ni(NO )
3 2
with HL, a portion of the Schiff base is hydrolyzed to produce a sal-
0
Crystal data for the two complexes are given in Table 1. Data
were collected with Mo K radiation, for 1 using a Bruker-AXS
icylaldehyde (L H) which along with the unhydrolyzed Schiff base
a
produce the hexa-coordinated hydrogen-bridged dinuclear species
0
SMART APEX II diffractometer and for 2 using an Oxford Diffraction
X-Calibur CCD System. A crystal of 1 was positioned 60 mm from
the CCD. Three hundred and sixty frames were measured with a
counting time of 5 s. Absorption corrections were carried out using
the SADABS program [37]. A crystal of 2 was positioned 50 mm from
[{NiLL (H
2
O)}
2
(
l
-H)]NO
3
2
ꢁH O (2) (Scheme 1). It is to be noted that
in 1 the chloride ion is coordinated to the metal centre, whereas in
2 the nitrate remains as a counter-anion, being H-bonded with the
water molecules (Section 3.2). We have observed earlier that some
Fe(III) and Cu(II) complexes of similar tridentate Schiff bases

S. Naiya et al. / Polyhedron 34 (2012) 67–73
69
Scheme 1. Synthesis of the complexes.
undergo hydrolysis if the anionic co-ligands do not coordinate to
2 2
3.2.1. Structure of [NiL(H O) Cl] (1)
the metal centre, as is observed in the formation of complex 2
The structure of 1 contains a crystallographic mirror plane and
shows the nickel in a six coordinate distorted octahedral environ-
ment, being bonded to the ligand L and a chloride ion in the equa-
torial mirror plane and two water molecules in axial positions. The
structure of 1 is shown in Fig. 1 together with the numbering
scheme in the metal coordination sphere. Bond distances and bond
angles are given in Table 2.
[
41,43,44]. However, it is very difficult to state the reason(s) for
this phenomenon with certainty as various factors, which are men-
tioned in Section 1, can control the hydrolysis.
3.2. Description of the structures
The bond lengths to the ligand L are Ni(1)–N(19) 2.014(6),
0
Ni(1)–O(11) 2.039(5) and Ni(1)–N(22) 2.167(6) ÅA , with Ni(1)–
0
Both compounds contain the ligand L, which coordinates merid-
Cl(1) 2.4251(17) AÅ . The Ni(1)–O(1) axial bond lengths to the water
0
ionally to Ni(II) forming an approximately planar donor set of car-
bonyl oxygen O(11), imine nitrogen N(19) and amino nitrogen
N(22).
molecules are 2.114(4) ÅA . All angles in the coordination sphere are
within 8° of 90 or 180°, thus showing little distortion from an ideal
octahedral geometry.
Fig. 1. The structure of 1 with ellipsoids at 30% probability. The structure is disordered around a mirror plane, but a discrete molecule is shown.

7
0
S. Naiya et al. / Polyhedron 34 (2012) 67–73
Table 2
0
Dimensions in the metal coordination spheres, distances, ÅA , angles, (°).
Compound 1
Compound 2
A
B
Bond lengths
Ni(1)–N(19)
Ni(1)–O(11)
Ni(1)–O(1)
Ni(1)–N(22)
Ni(1)–Cl(1)
2.014(6)
2.039(5)
2.114(4)
2.167(6)
2.425(2)
Ni–N(19)
Ni–O(31)
Ni–O(39)
Ni–O(1)
Ni–O(11)
Ni–N(22)
2.007(3)
2.011(2)
2.051(3)
2.110(3)
2.070(2)
2.165(3)
2.009(3)
1.982(2)
2.050(2)
2.092(2)
2.064(2)
2.169(3)
Bond angles
N(19)–Ni(1)–O(11)
N(19)–Ni(1)–O(1)
O(11)–Ni(1)–O(1)
90.28(19)
89.12(9)
89.10(9)
177.48(19)
82.6(2)
172.86(19)
90.78(9)
176.23(16)
93.49(12)
90.94(9)
N(19)–Ni–O(31)
N(19)–Ni–O(39)
O(31)–Ni–O(39)
N(19)–Ni–O(11)
O(31)–Ni–O(11)
O(39)–Ni–O(11)
N(19)–Ni–O(1)
O(31)–Ni–O(1)
O(39)–Ni–O(1)
O(11)–Ni–O(1)
N(19)–Ni–N(22)
O(31)–Ni–N(22)
O(39)–Ni–N(22)
O(11)–Ni–N(22)
O(1)–Ni–N(22)
177.20(10)
87.29(11)
90.39(10)
88.32(10)
93.22(9)
89.30(10)
91.51(10)
90.88(9)
179.16(11)
90.87(10)
89.59(9)
88.97(10)
91.71(8)
´
O(1)–Ni(1)–O(1)
N(19)–Ni(1)–N(22)
O(11)–Ni(1)–N(22)
O(1)–Ni(1)–N(22)
N(19)–Ni(1)–Cl(1)
O(11)–Ni(1)–Cl(1)
O(1)–Ni(1)–Cl(1)
N(22)–Ni(1)–Cl(1)
91.28(9)
89.95(11)
89.65(10)
174.89(10)
83.69(9)
84.07(11)
95.20(10)
94.83(10)
170.80(10)
90.27(10)
177.27(10)
88.22(9)
93.65(16)
83.67(11)
94.79(11)
90.44(10)
171.99(11)
91.86(11)
0
Symmetry element ( ) = x, 1.5 ꢀ y, z for 1.
0
+
2 2
In the [{NiLL (H O)} (l-H)] cation, the environments of the two
independent nickel atoms are very similar. Both are six-coordinate
octahedral, being bonded to the terdentate ligand L, the bidentate
0
ligand L and a water molecule. The equatorial plane can be consid-
ered as containing the donor atoms from the terdentate ligand L to-
0
gether with one oxygen O(31) from L . The rms deviations of the
0
four donor atoms in the two planes are 0.021 and 0.053 ÅA , with
0
the metal atoms 0.021(2) and 0.059(1) ÅA from the planes. Bond
lengths in the ligand L in the two molecules A and B, respectively,
0
0
are 2.070(2), 2.064(2) ÅA to O(11), 2.007(3), 2.009(3) ÅA to N(19)
0
and 2.165(3), 2.169(3) ÅA to N(22). The equatorial plane is com-
0
pleted by O(31) at 2.011(2) and 1.982(2) ÅA . The axial bond lengths
0
are 2.051(3), 2.050(2) to O(39) and 2.110(3), 2.092(2) ÅA to the
water molecule O(1).
0
The two oxygen atoms O(11A) and O(11B) are 2.450(3) ÅA apart. It
can therefore be concluded that there is a hydrogen atom between
them. The presence of the hydrogen atom also provides charge bal-
ance as there is a single nitrate anion in the asymmetric unit. How-
ever this hydrogen atom was not readily locatable in the difference
Fourier map although there was a broad positive area of electron
density between the two oxygen atoms. A hydrogen atom was intro-
duced into the refinement equidistant from the two oxygen atoms.
There are several other hydrogen bonds in the structure, involv-
ing the nitrate anion, the solvent water molecule O(1W), coordi-
nating water molecules and the phenolate oxygen atoms of the
complex. The dimensions are listed in Table 3 and illustrated in
Fig. 3. A significant feature of the structure of 2 is that the two
Fig. 2. The hydrogen bonds observed in the structure of 1 between the water
hydrogen atoms in one complex and adjacent complexes, thus forming a 1-D
polymer along the b axis. The complexes are disordered around mirror planes, but
only one set of coordinates for the atoms in the molecule is shown throughout.
Hydrogen bonds are shown as dotted lines.
The water molecule forms two hydrogen bonds to the molecule
0
at symmetry element ꢀx, ꢀy, 1 ꢀ z; O(1)–H(1)ꢁꢁꢁCl(1) 2.44 ÅA , O(1)–
0
0
HꢁꢁꢁCl 142° and O(1)ꢁꢁꢁCl(1) 3.159(4) ÅA and O(1)–H(2)ꢁꢁꢁO(11) 1.98 ÅA ,
0
O(1)–H(2)ꢁꢁꢁO(11) 154° and O(1)ꢁꢁꢁO(11) 2.772(4) ÅA . Thus a 1D
polymeric chain of molecules is formed along the crystallographic
b axis, as shown in Fig. 2.
phenoxo oxygen atoms of the coordinated Schiff base ligand (L)
0
of two equivalent [NiLL (H
2
O)] moieties are linked by symmetrical
Oꢁꢁꢁ( -H)ꢁꢁꢁO hydrogen bonding. This type of hydrogen bonding is
l
very rare in complexes of Schiff bases with metal ions [45–47].
There are about 20 mononuclear and one polynuclear com-
pound of Ni(II) which are reported in the literature with salicylal-
dehyde and ethylenediamine derived tridentate NNO donor Schiff
base ligands along with different anionic co-ligands [28–34].
Among the mononuclear compounds, there is one example with
acetate, two with sulfate, seven with thiocyanate and seven with
0
3
.2.2. Structure of [{NiLL (H
O)}
2 2
(l-H)]NO
3 2
ꢁH O (2)
0
The structure of 2 consists of two equivalent [NiLL (H
eties bridged by a hydrogen atom to give a [{NiLL (H
cation, which forms a set of hydrogen bonds together with a nitrate
ion and a solvent water molecule, as shown in Fig. 3. Bond dis-
tances and bond angles are given in Table 2.
2
O)] moi-
0
+
2
O)}
2
(l-H)]

S. Naiya et al. / Polyhedron 34 (2012) 67–73
71
0
2
O)} (l
-H)]+ cation in 2, together with a nitrate ion and a solvent water molecule. Ellipsoids are at 30% probability. Hydrogen bonds are
Fig. 3. The structure of the [{NiLL (H
2
shown as dotted lines.
Table 3
(theoretical 6.3%) between 60 and 145 °C in one step (Fig. S2). Like
0
Hydrogen bond dimensions (distances, ÅA , angles, (°) in 2. D = donor, A = acceptor.
compound 1, the dehydrated sample of 2 reabsorbs water mole-
cules on exposure in the open atmosphere within several minutes.
As the dehydrated species absorb the water molecules readily from
atmosphere we were not able to record the IR and electronic spec-
tra of the pure dehydrated species. The FT-IR spectra of the rehy-
drated species are identical to the original complexes.
D–H
A
d(HꢁꢁꢁA)
\DHA
d(DꢁꢁꢁA)
O(1A)ꢁꢁꢁH(1A)
O(1B)ꢁꢁꢁH(1B)
O(1B)ꢁꢁꢁH(1B)
O(11A)ꢁꢁꢁH(11)
O(1W)ꢁꢁꢁH(1)
O(1W)ꢁꢁꢁH(2)
O(31B)
O(4)
O(1W)
O(11B)
O(31A)
O(2)
1.86
1.88
1.90
1.23
1.82
2.04
156
165
160
177
170
157
2.652(3)
2.730(4)
2.717(4)
2.450(3)
2.695(4)
2.856(5)
3.4. IR spectra, magnetic moments and UV–Vis spectra of the
complexes
azide as co-ligands. Interestingly, the Ni(II) is square planar in all
such complexes but one, which is octahedral with a sulfate counter
ion [36]. In the sole polynuclear complex, all the nickel atoms are
in square pyramidal environments bridged by azide and having
perchlorate as the counter anion. Here, we have prepared two very
rare octahedral Ni(II) complexes of a terdentate Schiff base ligand
In the IR spectra of complexes 1 and 2, a strong and sharp band
ꢀ1
due to azomethine m(C@N) appears at 1635 and 1631 cm , respec-
ꢀ1
tively. The appearance of a broad band near 3377 and 3380 cm
indicates the presence of water molecules in 1 and 2, respectively,
as substantiated by their crystal structures. The sharp, strong peak
ꢀ
ꢀ
ꢀ1
with weak field anionic ligands, Cl and NO
3
. Thus it may be con-
at 1388 cm for complex 2 gives evidence for the presence of ionic
cluded that in the presence of strong field anionic co-ligands like
azide or thiocyanide, the ethylenediamine derived tridentate Schiff
base usually stabilizes a square planar geometry around Ni(II),
whereas a weak field co-ligand increases the chance of the stabil-
ization of octahedral complexes.
nitrate anion.
The room temperature magnetic moments of complexes 1 and 2
are 2.99 and 2.95 B.M., which is close to 2.83 B.M. and thus fits well
with the spin-only value for discrete magnetically non-coupled
nickel(II) systems.
The electronic spectra of these compounds are recorded in
methanol solution at room temperature. The electronic spectra
show d–d absorption bands at 587 and 887 nm for compound 1
and 595 and 887 nm for compound 2. These bands are assigned
3
.3. Thermogravimetric analysis
Thermogravimetric analysis shows that upon heating, complex
3
2g ? T1g(F) and 3
3
to the spin allowed transitions
A
A
2g ? T2g
,
1
loses the water molecules in one step, which starts at 78 °C and is
completed by 130 °C (Fig. S1). The observed weight loss of 11.1%
theoretical 11.0%) corresponds to two molecules of water per for-
respectively. The higher energy d–d bands are obscured by strong
ligand to metal charge-transfer transitions.
(
mula unit. The colour changes from green to reddish-brown on
dehydration. This dehydrated sample on exposing to open atmo-
sphere reabsorbs water molecules almost instantaneously and
the colour of the compound again changes to green. This rehy-
drated sample on heating shows a weight loss of ꢂ10.9% between
3.5. Solvatochromic properties of the complexes
Both complexes are colored red in less coordinating solvents,
such as dichloromethane or acetonitrile, having a lower donor
number (DN), whereas in more coordinating solvents (with a
7
0 and 130 °C. Similarly, complex 2 shows a weight loss 6.3%

7
2
S. Naiya et al. / Polyhedron 34 (2012) 67–73
4
. Conclusions
In the present study, we have synthesized two complexes with
a NNO donor Schiff base. In both, the geometry around Ni(II) is six-
coordinate distorted octahedral, which is very rare for complexes
of NNO donor Schiff bases derived from ethylenediamine deriva-
tives. The Schiff base undergoes hydrolysis during complex forma-
tion with Ni(NO
complex, [{NiLL (H
the reaction with NiCl
3
)
2
to result in a hydrogen bridged mixed ligand
O)} -H)]NO O, but remains intact during
ꢁH
. The results show that the hydrolysis of
0
2
2
(
l
3
2
2
the imine bonds in the Schiff base complexes of Ni(II) is dependent
on the counter anions. In solution, the colour of both complexes
depends upon the solvent used and this property may be attrib-
Fig. 4. Digital photograph of the colour of solutions of complex 1 in (a) MeOH (b)
DMSO, (c) CH Cl and (d) CH CN.
2
2
3
uted to the hypsochromic shift of the higher energy absorption
⁄
band (p–p
) with increasing 1‘DN of the solvent.
Acknowledgments
S.B. is thankful to CSIR, India for a research fellowship [Sanction
No. 09/028 (0732)/2008-EMR-I]. Crystallography of complex 1 was
performed at the DST-FIST, India-funded Single Crystal Diffractom-
eter Facility at the Department of Chemistry, University of Calcutta.
We also thank EPSRC and the University of Reading for funds for
the X-Calibur system.
Appendix A. Supplementary data
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
No. 846437 (1) and 846438 (2). Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk/deposit. Tel.: +44 01223 762910; fax: +44
0
1223 336033.
Supplementary data associated with this article can be found, in
Fig. 5. Solvatochromic behaviour of complex 1 in different solvents.
the online version, at doi:10.1016/j.poly.2011.12.014.
greater value of DN), such as DMSO or methanol, the solutions are
green (see in Fig. 4 for complex 1 and Fig. S3 for complex 2). The
colour of the complexes can be correlated with the coordinating
quality of the solvent, as measured by the Gutmann donor number
References
[1] S. Yamada, Coord. Chem. Rev. 192 (1999) 537.
[
[
[
2] M. Albrecht, Chem. Rev. 101 (2001) 3457.
3] R. Ziessel, Coord. Chem. Rev. 216/217 (2001) 195.
4] K.C. Gupta, A.K. Sutar, C.-C. Lin, Coord. Chem. Rev. 253 (2009) 1926.
(
DN) [48]. Spectroscopic data from the complexes reveal that only
the higher energy band around 370 nm, that may be assigned to
metal to ligand charge transfer (MLCT) transitions, changes consid-
erably with the change in solvent DN (Fig. 5 for complex 1 and
Fig. S4 for complex 2). Moreover, for both complexes, it is observed
that the band which appears as a single peak at 363 and 373 nm for
complex 1 and 364 and 375 nm for complex 2 in DMSO and meth-
anol, respectively, splits into two bands with maxima at about 324
and 383 nm for complex 1 and 323 and 381 nm for complex 2 in
acetonitrile and 333 and 391 nm for complex 1 and 326 and
[5] D. Zhang, H. Wang, Y. Chen, Z.-H. Ni, L. Tian, J. Jiang, Inorg. Chem. 48 (2009)
1215.
6] P. Mukherjee, M.G.B. Drew, C.J. Gómez-García, A. Ghosh, Inorg. Chem. 48
2009) 5848.
[7] E.C. Niederhoffer, J.H. Timmons, A.E. Martell, Chem. Rev. 84 (1984) 137.
1
[
(
[
8] E. Fujita, B.S. Brunschwig, T. Ogata, S. Yanagida, Coord. Chem. Rev. 132 (1994)
95.
9] T. Opstal, F. Verpoort, Angew. Chem., Int. Ed. 42 (2003) 2876.
1
[
[10] O. Khan, J. Galy, Y. Journax, J. Jaud, I.M. Badarau, J. Am. Chem. Soc. 104 (1982)
165.
2
[
[
11] J.-P. Costes, F. Dahan, A. Dupuis, Inorg. Chem. 39 (2000) 165.
12] Q. Wang, J. Zhang, C.F. Zhuang, Y. Tang, C.Y. Su, Inorg. Chem. 48 (2009) 287.
3
90 nm for complex 2 in dichloromethane (Fig. S4). The higher en-
ergy bands (320–360 nm) may be assigned to an intra-ligand tran-
sition [49–52].
[13] B. Sarkar, M.S. Ray, Y.-Z. Li, Y. Song, A. Figuerola, E. Ruiz, J. Cirera, J. Cano, A.
Ghosh, Chem. Eur. J. 13 (2007) 9297.
[
[
14] S. Chattopadhyay, M.G.B. Drew, C. Diaz, A. Ghosh, Dalton Trans. (2007) 2492.
15] C. Adhikary, S. Koner, Coord. Chem. Rev. 254 (2010) 2933.
A comparison of the spectral data in four solvents suggests that
the energy of the absorption maximum of this MLCT band in-
creases with increasing DN of the solvents, the effect is character-
ized as hypsochromism [52] suggesting that the DN parameter of
the solvent makes the dominant contribution to the shift in the
charge transfer absorption band. This behaviour is in accordance
with the interaction of the dipole moment of the solute complexes
and the surrounding solvent. It suggests that short-range interac-
tions between the dipole moment of the solute and the solvent
can induce structural changes of the solute complexes in accor-
dance with the alignment of the transition moment for ground
and excited states of a certain transition [51].
[16] K.C. Gupta, A.K. Sutar, Coord. Chem. Rev. 252 (2008) 1420.
[
[
17] K.L. Gurunatha, T.K. Maji, Inorg. Chem. 48 (2009) 10886.
18] T.K. Maji, G. Mostafa, R. Matsuda, S. Kitagawa, J. Am. Chem. Soc. 127 (2005)
17152.
[19] J. Tisato, F. Refosco, F. Bandoli, Coord. Chem. Rev. 135 (1994) 325.
[20] J. Lacroix, Eur. J. Inorg. Chem. (2001) 339.
[
[
[
[
21] S. Khatua, S.H. Choi, J. Lee, K. Kim, Y. Do, D.G. Churchill, Inorg. Chem. 48 (2009)
993.
22] D. Mandal, V. Bertolasi, J. Ribas-Ariño, G. Aromí, D. Ray, Inorg. Chem. 47 (2008)
3465.
2
23] B. Sarkar, M.S. Ray, M.G.B. Drew, A. Figuerola, C. Diaz, A. Ghosh, Polyhedron 25
(
2006) 3084.
24] Y.-B. Dong, X. Zhao, R.-Q. Huang, Inorg. Chem. 43 (2004) 5603. and reference
therein.

S. Naiya et al. / Polyhedron 34 (2012) 67–73
[40] ABSPACK, Oxford Diffraction Ltd., Oxford, UK, 2005.
73
[
[
[
25] S. Naiya, B. Sarkar, Y. Song, S. Ianelli, M.G.B. Drew, A. Ghosh, Inorg. Chim. Acta
63 (2010) 2488.
26] S. Chattopadhyay, P. Chakraborty, M.G.B. Drew, A. Ghosh, Inorg. Chim. Acta
62 (2009) 502.
27] C. Biswas, S. Chattopadhyay, M.G.B. Drew, A. Ghosh, Polyhedron 26 (2007)
411.
28] C.-B. Tang, Acta. Crystallogr., Sect. E 62 (2006) m2629.
29] C. Gonzalez-Arellano, E. Gutierrez-Puebla, M. Iglesias, F. Sanchez, Eur. J. Inorg.
Chem. (2004) 1955.
3
[41] R. Biswas, M.G.B. Drew, C. Estarellas, A. Frontera, A. Ghosh, Eur. J. Inorg. Chem.
(2011) 2558.
[42] S. Naiya, M.G.B. Drew, C. Diaz, J. Ribas, A. Ghosh, Eur. J. Inorg. Chem. (2011)
4993.
[43] P. Mukherjee, M.G.B. Drew, A. Ghosh, Eur. J. Inorg. Chem. (2008) 3372.
[44] M.S. Ray, R. Bhattacharya, S. Chaudhuri, L. Righi, G. Bocelli, G. Mukhopadhyay,
A. Ghosh, Polyhedron 22 (2003) 617.
[45] B.H. Courtney, B.W.O. Juma, S.F. Watkins, F.R. Fronczek, G.G. Stanley, Acta
Crystallogr. Sect. C 62 (2006) 268.
3
4
[
[
[
[
[
30] Z.-L. You, X. Han, J. Wang, S.-Y. Niu, Acta Crystallogr., Sect. E 62 (2006) m851.
31] C. Adhikary, D. Mal, S. Chaudhuri, S. Koner, J. Coord. Chem. 59 (2006) 699.
32] N. Mondal, S. Mitra, V. Gramilich, S.O. Ghodsi, K.M.A. Malik, Polyhedron 20
[46] D. Maity, P. Mukherjee, A. Ghosh, M.G.B. Drew, C. Diaz, G. Mukhopadhyay, Eur.
J. Inorg. Chem. (2010) 807.
(
2001) 135.
33] P. Mukherjee, M.G.B. Drew, C.J. Gómez-García, A. Ghosh, Inorg. Chem. 48
2009) 4817.
34] S. Naiya, H.-S. Wang, M.G.B. Drew, Y. Song, A. Ghosh, Dalton Trans. 40 (2011)
744.
[47] P. Mukherjee, C. Biswas, M.G.B. Drew, A. Ghosh, Polyhedron 26 (2007)
3121.
[48] V. Gutmann, The Donor–Acceptor Approach to Molecular Interactions, Plenum
Press, New York, London, 1978.
[49] A. Vogler, H. Kunkely, Coord. Chem. Rev. 251 (2007) 577.
[50] P. Kar, S. Verma, A. Sen, A. Das, B. Ganguly, H.N. Ghosh, Inorg. Chem. 49 (2010)
4167.
[
[
(
2
[
[
35] S. Chattopadhyay, M.G.B. Drew, A. Ghosh, Eur. J. Inorg. Chem. (2008) 1693.
36] S. Mukhopadhyay, D. Mandal, D. Ghosh, I. Goldberg, M. Chaudhury, Inorg.
Chem. 42 (2003) 8439.
[51] V.M. Leovac, L.S. Jovanovi c´ , V. Divjakovi c´ , A. Pevec, I. Leban, T. Armbruster,
[
[
[
37] SAINT, Version 6.02, SADABS, Version 2.03; Bruker AXS, Inc., Madison, WI, 2002.
38] CRYSALIS, Oxford Diffraction Ltd., Abingdon, UK, 2006.
39] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
Polyhedron 26 (2007) 49.
[52] H. Unver, A. Elmali, A. Karakas, H. Kara, E. Donmez, J. Mol. Struct. 800 (2006)
18.