Syntheses and characterizations of square planar nickel(II) complexes with pendant ligands: Examples of bi-dentate bonding modes of potentially tri- and tetra-dentate Schiff bases

Article abstract of DOI:10.1016/j.poly.2013.08.028

Four square planar nickel(II) complexes, [Ni(L¹)₂] (1), [Ni(L²)₂] (2), [Ni(L³)(NHEt₂)] (3) and [Ni(han)₂] (4), where HL¹ = 1-(3- hydroxypropyliminomethyl)naphthalene-2

Full text of DOI:10.1016/j.poly.2013.08.028

Polyhedron 65 (2013) 229–237
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Polyhedron
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Syntheses and characterizations of square planar nickel(II) complexes
with pendant ligands: Examples of bi-dentate bonding modes of
potentially tri- and tetra-dentate Schiff bases
Subhendu Bag, Prasanta Kumar Bhaumik, Subrata Jana, Mithun Das, Prasanta Bhowmik,
⇑
Shouvik Chattopadhyay
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Four square planar nickel(II) complexes, [Ni(L1)2] (1), [Ni(L2)2] (2), [Ni(L3)(NHEt2)] (3) and [Ni(han)2] (4),
where HL1 = 1-(3-hydroxypropyliminomethyl)naphthalene-2-ol, HL2 = 1-(5-hydroxy-3-oxapentylimi-
nomethyl)naphthalene-2-ol, H2L3 = 2-(2-hydroxy-3-methoxybenzylideneamino)phenol and Hhan =
1-hydroxy-2-acetonaphthone, have been prepared and characterized by elemental analyses, IR and
UV–Vis spectroscopy and single crystal X-ray diffraction studies. The potential tridentate ONO-donor
ligand HL1 and potential tetradentate ONOO-donor ligand HL2 coordinate the nickel(II) only through
the amine N and phenolic O to form complexes 1 and 2 respectively, i.e. the ligands act as pendant
ligands. On the other hand, the potential tetradentate ONOO-donor Schiff base H2L3 coordinates the nick-
el(II) only through the amine N atom and two phenolic O atoms to form complex 3, i.e. it also acts as
pendant ligand. Complex 4 is formed by the reaction of nickel(II) with 1-hydroxy-2-acetonaphthone.
Article history:
Received 11 May 2013
Accepted 6 August 2013
Available online 17 August 2013
Keywords:
Nickel(II)
Schiff base
Pendant
Crystal structure
H-bonding
H-bonding, C–HÁ Á Á
p
and
p
Á Á Áp
interactions form supra-molecular assembly.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
the purpose of carrying a radionuclide into a target cell [25], in
magnetic resonance imaging reagents [26] and for progressively
more elaborate investigations for their structure/activity relation-
ship [27,28]. A set of pendant donors can perturb the metal ion
at additional coordination sites, in competition with external sub-
strates, or can be used as attachment points for other molecules
[29].
The study of Schiff base ligand system is linked with many of
the key advances made in inorganic chemistry [1–8]. Among the
Schiff bases, salen-type ligands, which are formed by the conden-
sation of various diamines with salicylaldehyde derivatives, are
perhaps the most popular ones [9–15]. Condensation reaction of
salicylaldehyde or its derivatives with 2-aminoethanol or 3-ami-
no-1-propanol has also been exhaustively used to prepare ONO-
donor tridentate Schiff bases [16–18]. Incorporation of additional
functional groups into any ligand moiety has already been proved
to be synthetically more useful as they may interact with the other
molecules to form supra-molecular architecture [19–21]. In this re-
gard, hydrogen bonds have attracted considerable interest due to
their relative strength, directionality, and ability to act synergi-
cally, thus providing a directing force for the organization of indi-
vidual molecules into well-defined supra-molecular assemblies
[22,23].
The condensation of 2-hydroxy-1-naphthaldehyde with 2-ami-
noethanol produces ONO-donor tridentate Schiff base, which has
already been used to prepare several transition metal complexes
[30–33]. The Schiff base produced by the condensation of 2-amino-
phenol with 2-hydroxy-1-naphthaldehyde has already been used
to prepare nickel(II) complex [34]. However, the potential tetra-
dentate Schiff base, produced by the condensation of o-vanillin
and 2-aminophenol, has not been used to prepare nickel(II) com-
plex till date. We have used this ligand in the present study to pre-
pare nickel(II) complex. On the other hand, the Schiff bases,
produced by the condensation of 2-hydroxy-1-naphthaldehyde
with 3-amino-1-propanol or 2-(2-aminoethoxy)ethanol, have also
not been used in preparing transition metal complexes till date.
We have used these two amines to prepare Schiff bases with 2-hy-
droxy-1-naphthaldehyde, which are, in turn, used to form nickel(II)
complexes. It seems interesting to conduct a systematic study on a
designed series of transition metal complexes with the intention to
understand the way in which H-bonding interactions cooperate
The term ‘pendant ligand’ is applied a to potential polydentate
ligand that has additional donor groups attached to its periphery.
A large number of pendant ligands are produced for a variety of dif-
ferent chemical applications, e.g. in enzyme simulations [24], for
⇑
Corresponding author. Tel.: +91 33 24572941.
E-mail address: shouvik.chem@gmail.com (S. Chattopadhyay).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.08.028

230
S. Bag et al. / Polyhedron 65 (2013) 229–237
and direct the supra-molecular assembly of the molecular building
blocks with variation in the ligand moieties.
In the present paper, we would like to report the synthesis,
characterization and crystal structures of four new nickel(II) com-
plexes, of which three contain pendant Schiff bases.
(KBr, cmÀ1
max(dm3 molÀ1 cmÀ1)] (DMF) 436 (3425), 595 (125). Magnetic
moment: diamagnetic.
)
1620
(
mC@
@
N), 3420 (mOH); UV–Vis, kmax (nm)
[e
2.1.3. Synthesis of [Ni(L3)(NHEt2)] (3)
Ortho-vanillin (1 mmol, 152 mg) and 2-aminophenol (1 mmol,
109 mg) in methanol (30 ml) was refluxed for 1 h to prepare the
tridentate Schiff base ligand, 2-(2-hydroxy-3-methoxybenzylide-
neamino)phenol (H2L3). The ligand was not isolated and used di-
rectly for the preparation of complex 3. A methanol solution of
Ni(ClO4)2Á6H2O (1 mmol, 365 mg) was added to the methanol solu-
tion of the ligand and refluxed for 1 h to give a brown solution. Few
drops of diethyl amine (0.4 ml) were added to it and refluxed for an
additional hour to get a dark brown solution. It was cooled and
kept for few days to get brown crystals, which were collected by
filtration. Deep brown single crystals, suitable for X-ray diffraction,
were obtained after few weeks on slow evaporation of the DMF
solution in open atmosphere.
2. Experimental
All chemicals were of reagent grade and were used without
further purification.
2.1. Preparations
2.1.1. Synthesis of [Ni(L1)2] (1)
A methanol solution of 3-amino-1-propanol (1 mmol, 0.075 ml)
and 2-hydroxy-1-naphthaldehyde (1 mmol, 172 mg) in methanol
(25 ml) were refluxed for 1 h to prepare the Schiff base ligand, 1-
(3-hydroxypropyliminomethyl)naphthalene-2-ol (HL1). It was not
isolated. The yellow coloured methanol solution of the ligand
was cooled and a methanol solution of NiCl2Á6H2O (0.5 mmol,
119 mg) was added to it and refluxed again for an additional hour.
A green crystalline solid was separated out after 2 days and col-
lected by filtration. Bright green single crystals, suitable for X-ray
diffraction, were obtained from CH3CN solution of the complex
on slow evaporation in open atmosphere.
Yield: 210 mg (56%). Anal. Calc. for C18H22N2NiO3 (FW 373.07):
C, 57.95; H, 5.94; N, 7.51. Found: C, 57.8; H, 5.8; N, 7.4. IR (KBr,
cmÀ1): 1593 (mC@
N), 2973 (mC–H), 3239 (mN–H), UV–Vis, kmax (nm)
@
[
emax (dm3 mol–1 cm–1)] (acetonitrile) = 420 (1.4 Â 104). Magnetic
moment: diamagnetic.
2.1.4. Synthesis of [Ni(han)2] (4)
A methanol solution (10 ml) of NiCl2Á6H2O (0.5 mmol, 119 mg)
was added to a methanol solution (10 ml) of 1-hydroxy-2-aceto-
naphthone (Hhan) (1 mmol, 186 mg) and the solution was refluxed
for 1.5 h. Red crystalline solid was obtained after few days and was
collected by filtration. X-ray quality single crystals were obtained
from DMF solution.
Yield: 230 mg (44%), Anal. Calc. for C28H28N2NiO4 (FW 515.23):
C, 65.27; H, 5.48; N, 5.44. Found: C, 65.1; H, 5.6; N, 5.4%. IR
(KBr, cmÀ1
)
1620
emax (dm3 molÀ1 cmÀ1)] (DMF) 415 (3353). Magnetic moment:
diamagnetic.
(
mC@
@
N), 3400 (mOH); UV–Vis, kmax (nm)
[
2.1.2. Synthesis of [Ni(L2)2] (2)
Yield: 140 mg (33%), Anal. Calc. for C24H18Ni2O4 (FW 429.09): C,
67.18; H, 4.23. Found: C, 67.2; H, 4.2%. IR (KBr, cmÀ1) 1585 (mC
O);
@
A solution of 2-(2-aminoethoxy)ethanol (1 mmol, 0.104 ml) in
methanol was added drop wise to a methanol solution (25 ml) of
2-hydroxy-1-naphthaldehyde (1 mmol, 172 mg). After complete
addition, the solution was stirred for 1.5 h to prepare the Schiff
base ligand 1-(5-hydroxy-3-oxapentyliminomethyl) naphthalene-
2-ol (HL2). The ligand was not isolated. A methanol solution
(10 ml) of NiCl2Á6H2O (0.5 mmol, 119 mg) was added to the meth-
anol solution of HL2 and the mixture was stirred for 3 h. A green
crystalline solid was separated out after few days and collected
by filtration. Diffraction quality single crystals were obtained after
a few days on slow evaporation of dark green acetonitrile solution
of the complex in open atmosphere.
UV–Vis, kmax (nm) [
e
max (dm3 molÀ1 cmÀ1)] (DMF) 432 (3438), @549
(143). Magnetic moment: diamagnetic.
2.2. Physical measurements
Elemental analysis (carbon, hydrogen and nitrogen) was per-
formed using a Perkin–Elmer 240C elemental analyzer. IR spectra
in KBr (4500–500 cmÀ1) were recorded using a Perkin–Elmer Spec-
trum Two FT-IR Spectrometer. Electronic spectra in acetonitrile
(1200–350 nm) were recorded in a Hitachi U-3501 spectropho-
tometer. Fluorescence spectra were obtained on HORIBA Jobin
Yvon FluoroMax-P spectrophotometer at room temperature. The
magnetic susceptibility measurements were done with an EG&PAR
Yield: 150 mg (26%), Anal. Calc. for C30H32NiN2O6 (FW 575.28):
C, 62.63; H, 5.61; N, 4.87; Found: C, 62.5; H, 5.7; N, 4.9%. IR
Table 1
Crystal data and refinement details of complexes 1, 2, 3 and 4.
1
2
3
4
Formula
Formula weight
Crystal system
Space group
a (Å)
C
28H28N2NiO4
C30H32N2NiO6
575.27
monoclinic
P21/c
11.8310(4)
5.1261(2)
21.7184(8)
90.227(2)
2
C18H22N2NiO3
373.07
monoclinic
P21/c
15.717(2)
9.2979(14)
11.9896(18)
93.084(2)
4
C24H18NiO4
429.07
monoclinic
P21/n
4.8371(2)
18.1658(8)
10.8164(5)
99.195(3)
2
515.21
monoclinic
P21/n
14.0979(5)
4.9115(2)
17.2567(5)
90.975(2)
2
b (Å)
c (Å)
b (°)
Z
Dcalc (g cmÀ3
1.432
0.850
1.451
0.785
1.416
1.127
1.519
1.063
)
l
(mmÀ1
)
F(000)
540
604
784
444
Total reflection
Unique reflections
Observed data [I > 2
Rint
17,950
2556
2040
0.042
10,453
2706
2052
0.036
13,066
3842
3073
0.032
13,750
2026
1430
0.057
r
(I)]
R1, wR2 (all data)
R1, wR2 [I > 2r(I)]
0.0425, 0.0811
0.0303, 0.0735
0.0509, 0.1283
0.0341, 0.1076
0.0359, 0.0784
0.0292, 0.0750
0.0794, 0.1562
0.0535, 0.1408

S. Bag et al. / Polyhedron 65 (2013) 229–237
231
Table 2
data are summarized in Table 1 and important bond lengths and
angles are listed in Table 2.
Selected bond lengths (Å) and bond angles (°) for complexes 1, 2, 3 and 4.
1
2
3
4
Ni(1)–O(1)
Ni(1)–N(1)
Ni(1)–O(2)
Ni(1)–N(2)
O(1)–Ni(1)–N(1)
O(1)–Ni(1)–O(2)
O(1)–Ni(1)–N(2)
O(2)–Ni(1)–N(1)
O(2)–Ni(1)–N(2)
N(1)–Ni(1)–N(2)
1.8220(13)
1.9064(14)
–
–
1.8237(17)
1.9118(18)
–
–
91.86(8)
–
1.842(1)
1.854(1)
1.828(1)
1.943(2)
87.35(6)
175.36(6)
90.66(6)
96.22(6)
86.04(6)
174.47(7)
1.852(3)
–
1.827(2)
3. Results and discussion
3.1. Synthesis
92.42(6)
The condensation of 2-aminoethanol with 2-hydroxy-1-naph-
thaldehyde produces the tridentate Schiff base, 1-(2-hydroxyeth-
ylimino)methyl)naphthalen-2-ol. This was already used to
prepare mononuclear complex with nickel(II) [37], in which
the potential tridente Schiff base acted as a bidentate one keep-
ing one donor site pendant (Scheme 1). In the present work, we
have used 3-amino-1-propanol instead of 2-aminoethanol in or-
der to examine changes, if any, in the resulting complexes on
incorporation of methylene spacer into the Schiff base moiety.
Facile condensation of it with 2-hydroxy-1-naphthaldehyde
afforded a potential tridentate neutral Schiff base, HL1 (1-(3-
hydroxypropyliminomethyl)naphthalene-2-ol). We have also
used 2-(2-aminoethoxy)ethanol in the present work to prepare
a potential tetradentate Schiff base, HL2 (1-(5-hydroxy-3-oxap-
entyliminomethyl)naphthalene-2-ol). When HL1 and HL2 are
made to react with nickel(II) separately, square planar com-
plexes are formed where both of them act as bidentate ligands,
keeping the side arms with potential donor atoms pendant
(Scheme 1).
–
–
–
–
–
92.95(12)
–
–
–
vibrating sample magnetometer, model 155 at room temperature
and diamagnetic corrections were made using Pascal’s constants.
2.3. X-ray crystallography
Single crystals of the complexes having suitable dimensions
were used for data collection using a Bruker SMART APEX II diffrac-
tometer equipped with graphite-monochromated Mo Ka radiation
(k = 0.71073 Å) at 293 K. The molecular structures were solved by
direct methods and refinement by full-matrix least squares on F2
using the SHELX-97 package [35]. Non-hydrogen atoms were refined
with anisotropic thermal parameters. The H atoms, attached with
O atoms, were located by difference Fourier maps and were kept
fixed. All other hydrogen atoms were placed in their geometrically
idealized positions and constrained to ride on their parent atoms.
Multi-scan empirical absorption corrections were applied to the
data using the program SADABS [36]. Significant crystallographic
On the other hand, the condensation of 2-aminophenol (instead
of 2-aminoethanol) with 2-hydroxy-1-naphthaldehyde produces
the tridentate Schiff base, (2-hydroxyphenyliminomethyl)naph-
thalene-2-ol. This was already used to prepare mononuclear com-
plex with nickel(II) [34], in which the fourth coordination site of
the metal is occupied by diethylamine molecule, used as base
Scheme 1. Synthesis of 1 and 2 and a related complex.

232
S. Bag et al. / Polyhedron 65 (2013) 229–237
Scheme 2. Synthesis of 3 and a related complex.
Scheme 3. Synthesis of 4.
Fig. 1. Perspective view of the centrosymmetric complex [Ni(L1)2] (1). Only the relevant atoms are labelled.
during the preparation (Scheme 2). In the present work, we have
used o-vanillin and 2-aminophenol to prepare a different Schiff
base H2L3 (2-(2-hydroxy-3-methoxybenzylideneamino)phenol).
The ligand is a potential tetradentate ligand with two phenolic
oxygen atoms, an imine N atom and a methoxy O atom. In the pres-
ent case, it uses its three donor atoms. The methoxy O remains as
pendant. The binegative ligand neutralizes charge of central square
planar nickel(II). The fourth coordination site of nickel(II) is occu-
pied by a diethyl amine molecule (Scheme 2).
It is interesting to note here that the use of 1-hydroxy-2-aceto-
naphthone instead of 2-hydroxy-1-naphthaldehyde followed by
the addition of nickel(II) produces complex 4, which is the

S. Bag et al. / Polyhedron 65 (2013) 229–237
233
Fig. 2. 2D H-bonded layer structure of complex 1. Only the relevant H atoms are shown for clarity. Symmetry element ! = 5/2 À x,1/2 + y,5/2À z.
Table 3
nickel(II) complex of 1-hydroxy-2-acetonaphthonate. The Schiff
base formed is most probably hydrolyzed in presence of nickel(II)
chloride. Hydrolysis of tridentate Schiff base in presence of
nickel(II) chloride has already been reported in the literature [38]
Addition of nickel(II) chloride to the methanol solution of 1-hydro-
xy-2-acetonaphthone could also produce complex 4 (Scheme 3).
Hydrogen bond distances (Å) and angles (°) of complexes 1 and 2.
Complexes
D–HÁ Á ÁA
D–H
DÁ Á ÁA
2.784
2.804
HÁ Á ÁA
2.05
xD–HÁ Á ÁA
171
1
2
O(2)–H(2)Á Á ÁO(2)!
0.74
0.82
O(3)–H(2)Á Á ÁO(2)$
1.990
171.9
D, donor; H, hydrogen; A, acceptor; symmetry element ! = 5/2Àx,1/2 + y,5/2À z,
$ = 2 À x,1 À y,Àz.
Fig. 3. (a) 1D supramolecular chain structure of complex 1 generated through the C–HÁ Á Á
Symmetry element ⁄ = 1 À x,1 À y,Àz.
p and pÁ Á Áp interactions. (b) The C–HÁ Á Áp and pÁ Á Áp interactions are highlighted.

234
S. Bag et al. / Polyhedron 65 (2013) 229–237
Table 4
Geometric features (distances in Å and angles in degrees) of the C–HÁ Á Áp interactions obtained for 1, 3 and 4.
Complexes
C–HÁ Á ÁCg(Ring)
HÁ Á ÁCg (Å)
C–HÁ Á ÁCg (°)
CÁ Á ÁCg (Å)
Symmetry
1
3
4
C(8)–H(8A)Á Á ÁCg(1)
C(10)–H(10)Á Á ÁCg(1)
C(1)–H(1C)Á Á ÁCg(1)
2.90
2.98
2.68
117
140
138
3.444(2)
3.740(2)
3.450(4)
x,À1 + y,z
1 À x,1/2 + y,1/2Àz
1 + x,y,z
For complex 1, Cg(1) = centre of gravity of ring [Ni(1)–O(1)–C(1)–C(6)–C(7)–N(1)]; in case of complex 3, Cg(1) = Ni(1)–O(1)–C(13)–C(8)–N(1) and for complex 4,
Cg(1) = Centre of gravity of ring [Ni(1)–O(1)–C(2)–C(3)–C(12)–O(2)].
Table 5
Geometric features (distances in Å and angles in degrees) of the
pÁ Á Áp interactions obtained for 1 and 4.
Complex
Cg(RingI)Á Á ÁCg(Ring J)
CgÁ Á ÁCg
a
b
c
Cg(I)Á Á ÁPerp
Cg(J)Á Á ÁPerp
Symmetry
1
4
Cg(1)Á Á ÁCg(3)
Cg(3)Á Á ÁCg(4)
4.0762(11)
3.923(2)
0.81(8)
0.39(18)
34.16
27.96
34.32
27.58
3.3668(6)
3.4769(15)
3.3729(8)
3.4647(16)
x,À1 + y,z
1 + x,y,z
a
= Dihedral angle between ring I and ring J (°); b = angle Cg(I) ? Cg(J) or Cg(I) ? Me vector and normal to plane I (°); c = Angle Cg(I) ? Cg(J) vector and normal to plane J (°);
Cg(I)Á Á ÁPerp = Perpendicular distance of Cg(I) on ring J; Cg(J)Á Á ÁPerp = Perpendicular distance of Cg(J) on ring I; Cg(1) = centre of gravity of ring [Ni(1)–O(1)–C(1)–C(6)–C(7)–
N(1)]; Cg(2) = centre of gravity of ring [Ni(1)–O(I)⁄–C(1)⁄–C(6)⁄–C(7)⁄–N(1⁄)]; Cg(3) = centre of gravity of ring [C(1)–C(2)–C(3)–C(4)–C(5)–C(6) for complex
1 and
Cg(3) = centre of gravity of ring [C(3)–C(4)–C(5)–C(6)–C(11)–C(12)]; Cg(4) = centre of gravity of ring [C(6)–C(7)–C(8)–C(9)–C(10)–C(11)] for complex 4.
two-dimensional supramolecular network (Fig. 2). The details of
H-bonding are given in Table 3.
Complex 1 represents combination of
p
Á Á Á
p
and C–HÁ Á Á
p inter-
actions in the solid-state structure that contributes to the self
assembly process. The chelate ring, Cg(1), present in the molecule
{Cg(1) = Centre of gravity of ring [Ni(1)–O(1)–C(1)–C(6)–C(7)–
N(1)]} shows
a
C–HÁ Á Á
p interaction with symmetry related
C(methylene)–H group of C(8) where the H(8A)Á Á ÁCg(1) distance
is 2.90 Å and the C(8)–H(8A)Á Á ÁCg(1) angle is 117°. Such small va-
lue of C–HÁ Á ÁCg angle is already reported in several papers [39,40].
The chelate ring again creates a
pÁ Á Áp interaction with the phenyl
ring Cg(3) of symmetry related adjacent moiety. As the molecule
is centrosymmetric, same types of C–HÁ Á Á
p
and interactions
p p
Á Á Á
are observed in its centrosymmetric counterpart. The one dimen-
sional supramolecular architecture has been formed by the combi-
nation of the C–HÁ Á Á
p
and
and
p
p
Á Á Á
p
interactions (Fig. 3). Geometric
interactions are given in Tables
features of the C–HÁ Á Á
p
Á Á Á
p
4 and 5 respectively.
3.2.2. Complex [Ni(L2)2] (2)
Complex 2 crystallizes in the monoclinic space group P21/c. A
perspective view of complex 2 with selective atom-numbering
scheme is shown in Fig. 4. The structure determination reveals that
the complex consists of a discrete centrosymmetric mononuclear
unit [Ni(L2)2]. The potential tetradentate ligand, HL2, behaves like
a bidentate mono-negative ligand with the hydroxyl and oxo
(ethereal) groups remaining uncoordinated and not de-protonated.
The nickel(II) is coordinated by two imine nitrogen atoms, N(1) and
N(1)# and two phenolate oxygen atoms, O(1) and O(1)# of the two
molecules of the Schiff base ligand (# = 2 À x, Ày,2 À z
Fig. 4. Perspective view of the centrosymmetric complex [Ni(L2)2] (2). Only the
relevant atoms are labelled.
3.2. Structure description
3.2.1. Complex [Ni(L1)2] (1)
Complex 1 crystallizes in the monoclinic space group P21/n. A
perspective view of complex 1 with selective atom-numbering
scheme is shown in Fig. 1 and important bond lengths and angles
are listed in Table 2. The structure determination reveals that the
complex consists of a discrete centrosymmetric mononuclear unit
[Ni(L1)2]. The potential tridentate ligand, HL1, behaves like a biden-
tate mono-negative ligand with the hydroxyl group remaining
uncoordinated and not de-protonated. The nickel(II) is coordinated
by two imine nitrogen atoms, N(1) and N(1)⁄ and two phenolate
oxygen atoms, O(1) and O(1)⁄ of the two Schiff base ligands
(⁄ = 1 À x,1 À y,Àz).
The hydrogen atom, H(2), attached with O(3) of the uncoordi-
nated hydroxyl and O(2) are engaged in hydrogen bond formation
with symmetry related (2 À x,1Ày,Àz) oxygen atoms, O(2) and
O(3) respectively to form a one dimensional chain (Fig. 5). The
details of H-bonding are given in Table 3. There are no significant
C–HÁ Á Á
p
or
pÁ Á Áp interactions in the complex 2.
3.2.3. [Ni(L3)(NHEt2)] (3)
The complex 3 crystallized in the monoclinic space group, P21/c.
The discrete mononuclear units of the nickel(II) complex with
selective atom-labeling scheme is shown in Fig. 6. The structure
determination reveals that the tridentate Schiff base ligand, H2L3
coordinates to the nickel atom, Ni(1) via the phenolate oxygen
atom, O(1), imine nitrogen atom, N(1) and another phenolate oxy-
gen atom, O(2), forming one five and one six membered chelate
There is one available H atom, H(2), for hydrogen bond forma-
tion, which is involved in strong hydrogen bonding with the oxy-
gen atom, O(2) of the pendant hydroxyl group of
a
crystallographically related unit (5/2 À x,1/2 + y,5/2 À z), giving a

S. Bag et al. / Polyhedron 65 (2013) 229–237
235
Fig. 5. H-bonded chain of complex 2. Only the relevant H atoms are shown for clarity. Symmetry element $ = 2 À x,1 À y,Àz.
3.2.4. Complex Ni(han)2 (4)
Complex 4 crystallizes in monoclinic space group P21/n. The
structure of 4 is shown in Fig. 8 together with selective atom-num-
bering scheme in the metal coordination spheres. The asymmetric
unit consists of a discrete centrosymmetric mononuclear unit
Ni(han)2. Nickel atom is square planar and is bonded to four oxy-
gen atoms from two bidentate 1-hydroxy-2-acetonaphthone li-
gands in the equatorial plane. Bond lengths range from 1.832(3)
to 1.861(3) Å. The distances between nickel(II) and the phenoxy
O atom is shorter than that between the nickel(II) and the carbonyl
O atom, as is usual for this type of complexes [41].
The complex shows significant C–HÁ Á Á
One C(methyl)–H group, C(1)–H(1C) of the ligand (Hhan) shows a
interaction with a chelate ring Cg(1) of symmetry related
p
and
p
Á Á Á
p interactions.
C–HÁ Á Á
p
moiety, where the H(1B)Á Á ÁCg(1) distance is 2.68 Å and the C(1)–
H(1C)Á Á ÁCg(1) angle is 138°. The phenyl ring Cg(3) of the ligand
(Hhan) shows a
p p interaction with symmetry related Cg(4).
Á Á Á
As the molecule is centrosymmetric, same type of C–HÁ Á Á
Á Á Á interactions are observed in its centrosymmetric counter-
part, as is observed in 1. 1D crystalline supramolecular architecture
p and
p
p
of complex 4 has been formed by the combination of the C–HÁ Á Á
p
p
and
and
pÁ Á Áp
p
interactions (Fig. 9). Geometric features of the C–HÁ Á Á
Fig. 6. Perspective view of the complex 3. Only the relevant atoms are labelled.
pÁ Á Á
interactions are given in Tables 4 and 5 respectively.
3.3. IR and UV–Vis spectra, fluorescence and magnetic moment
rings. The diethyl amine nitrogen atom, N(2), occupies the fourth
coordination site forming a slightly distorted square-planar geom-
etry 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 0.0680(13), 0.0662(13), À0.0668(13) and
À0.0674(17) Å respectively. This deviation from planarity is also
manifesting itself in the trans angles {O(1)–Ni(1)–O(2), N(1)–
Ni(1)–N(2)} which are 175.36(6) and 174.47(7). The deviation of
the nickel(II) ion from the said equatorial plane is 0.0173(2) Å.
There is no H-bond present in complex 3.
In the IR spectra of the complexes 1 and 2, distinct bands due to
the azomethine (C@N) group within 1612–1620 cmÀ1 are custom-
arily noticed [42]. The characteristic imine stretches for complex 3
appear as a strong signal in the region 1593 cmÀ1. A broad band
around 3428 cmÀ1 in complexes 1 and 2 are assigned to the OH
stretching vibration of the molecules, which are involved in hydro-
gen bonding [43]. The band at 3239 cmÀ1 in the IR spectrum of
complex 3 is assigned as N–H stretching of diethyl amine [44].
Complex 4, shows a very intense band for C=O (ketone) stretching
at 1585 cmÀ1 and a medium strong band at 1240 cmÀ1 is assigned
to the C–O (phenoxy) stretching frequency [41].
In the electronic spectra, the lack of any transition at longer
wavelengths (below 600 nm) indicates a large crystal-field split-
ting and is consistent with the square planar geometry of nickel(II)
[45]. However, high intensity absorption bands in the UV region
indicate LMCT transitions. Absorption bands due to d–d transition
occur below 600 nm. In the absorption spectra of complexes 1 and
3, the d–d transition bands at about 550 nm cannot be observed as
The complex 3 shows a single type of C–HÁ Á Á
of the aromatic hydrogen of C(aryl)–H group, C(10) in the Schiff
interaction with the five membered che-
p interaction. One
base of 3 shows C–HÁ Á Á
p
late ring present in complex 3 of another adjacent moiety where
the H(10)Á Á ÁCg(1) distances are 2.98 Å and C(10)–H(10)Á Á ÁCg(1)
angles are 140°. Because of this type of interaction a 1D array
in zigzag fashion has been formed in the crystal packing of 3
(Fig. 7). Geometric features of the C–HÁ Á Á
p interactions are given
in Table 4.

236
S. Bag et al. / Polyhedron 65 (2013) 229–237
Fig. 7. One-dimensional zigzag array of complex 3 via CÀHÁ Á Á
p interactions.
Table 6
Photophysical data for the complexes 1–4.
Complex
Absorption (nm)
Emission (nm)
1
2
3
4
415
420
420
425
454
477
480
481
they are obscured by strong charge transfer transitions. Complexes
1, 2 and 4 are only partly soluble in acetonitrile, and so their
absorption spectra were taken in DMF solution. Complex 3 is freely
soluble in acetonitrile and its spectrum is run in acetonitrile
solution.
Fig. 8. Perspective view of the a centrosymmetric complex Ni(han)2 (4). Only the
relevant atoms are labelled.
Fig. 9. (a) 1D supramolecular chain of complex 4, generated through C–HÁ Á Á
p and pÁ Á Áp interactions (b) The C–HÁ Á Áp and pÁ Á Áp interactions are highlighted. Symmetry
element # = 2 À x,Ày,2 À z.

S. Bag et al. / Polyhedron 65 (2013) 229–237
[7] P.G. Lacroix, Eur. J. Inorg. Chem. 2 (2001) 339.
(p ?
p⁄). The spectroscopic data are given in
237
Complexes 1–4 show fluorescence. These are assigned as intral-
igand fluorescence
Table 6 (without solvent correction) [46].
1
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Complexes 1, 2, 3 and 4 are diamagnetic as expected for the
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The isolation and crystal structure determination of the com-
plexes unambiguously show that the potential tri and tetradentate
Schiff bases are acting as bi-dentate ligands. The hydroxyl groups
remain as pendant. These hydroxy groups are capable of forming
H-bonds and several supra-molecular architectures are produced.
Thus it opens up new possibilities for the synthesis of complexes
having pendant ligands. On the other hand, use of 1-hydroxy-2-
acetonaphthone as the carbonyl complex could not produce the ex-
pected Schiff base complex with nickel(II); we are getting nickel(II)
1-hydroxy-2-acetonaphthonate as the final product. H-bonding, C–
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HÁ Á Á
p
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Á Á Á
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Acknowledgements
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This work was supported by the CSIR, India (Fellowship for Pra-
santa Bhowmik, Sanction No. 09/096(0607)/2010-EMR-I, dated
27.1.10 and Fellowship for Subrata Jana, Sanction No. 09/
096(0659)/2010-EMR-I, dated 18.1.11). Crystallographic data were
performed at the DST-FIST, India-funded single crystal diffractom-
eter facility at the Department of Chemistry, Jadavpur University.
Appendix A. Supplementary data
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Ghosh, Eur. J. Inorg. Chem. (2005) 4562.
CCDC 927221, 927222, 937850 and 927223 contains the sup-
plementary crystallographic data for 1, 2, 3 and 4 respectively.
These data can be obtained free of charge via http://www.ccdc.ca-
m.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
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