Bis(μ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes: Tandem synthesis, structure and self assembly

Article abstract of DOI:10.1016/j.poly.2014.11.012

Two new bis(μ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes [Ni₂L¹₂(PTZ)₂]·2(CH₃)₂SO·2.69H₂O (1) and 2[Ni₂L²₂(PTZ)₂

Full text of DOI:10.1016/j.poly.2014.11.012

Accepted Manuscript
Bis(μ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes: Tan-
dem synthesis, structure and self assembly
Mithun Das, Klaus Harms, Biswa Nath Ghosh, Kari Rissanen, Shouvik
Chattopadhyay
PII:
S0277-5387(14)00719-0
DOI:
http://dx.doi.org/10.1016/j.poly.2014.11.012
POLY 11060
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
30 August 2014
12 November 2014
Please cite this article as: M. Das, K. Harms, B.N. Ghosh, K. Rissanen, S. Chattopadhyay, Bis(μ-tetrazolato-NN′)
bridged dinuclear nickel(II) Schiff base complexes: Tandem synthesis, structure and self assembly, Polyhedron
(2014), doi: http://dx.doi.org/10.1016/j.poly.2014.11.012
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Bis(µ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff
base complexes: Tandem synthesis, structure and self
assembly
Mithun Dasa, Klaus Harmsb, Biswa Nath Ghoshc, Kari Rissanenc, Shouvik
Chattopadhyaya,*
a Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata – 700 032, India.
E-mail: shouvik.chem@gmail.com Tel:+91-33-24572941
bFachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, D-35032
Marburg, Germany.
c Department of Chemistry, Nanoscience Center, University of Jyväskylä, P.O. Box 35, 40014
Jyväskylä, Finland.
Abstract
Two new bis(µ-tetrazolato-NN′) bridged centrosymmetric dinuclear nickel(II) Schiff base
complexes [Ni2L1 (PTZ)2]·2(CH3)2SO·2.69H2O (1) and 2[Ni2L2 (PTZ)2]·3H2O (2) (HL1 and HL2
2
2
are Schiff bases, HL1 = 2-((2-(dimethylamino)ethylimino)methyl)phenol, HL2 = 2-((2-
(methylamino)ethylimino)methyl)-6-methoxyphenol and HPTZ is 5-pyrazinyltetrazole) have been
synthesized via [3+2] cyclo-addition of 2-cyanopyrazine and sodium azide in presence of
nickel(II) acetate tetrahydrate and the respective Schiff bases. The structures of the complexes
are confirmed by single crystal X-ray diffraction analysis. Both complexes show fluorescence
1

with fluorescence life times in the range 1 - 6 ns. The change in the denticity of the Schiff base
blocking ligand was shown to have no effect in controlling the molecular structures of the
complexes. The supramolecular self assemblies were also explored.
Key words: Nickel(II); Schiff base; 1,3-dipolar cycloaddition; 5-pyrazinyltetrazolate; Dinuclear.
Introduction
Di and polynuclear complexes of nickel(II) are widely used as materials for non-linear
optics [1,2], as catalysts for diverse reactions [3] and as suitable models for the active sites of
many enzymes [4-6] and also as magnetic materials [7-9]. Several researchers have used
carboxylates and pseudohalides as bridging ligands [10-12]. N2O donor tridentate Schiff bases,
prepared simply by refluxing N-substituted diamines with salicylaldehyde or its derivatives, as
blocking ligands in preparing such di and polynuclear complexes [13-15]. The ability of the
phenoxo oxygen atom to bridge the metal centres and also to participate in hydrogen bonding
interaction to form various supramolecular architectures has also inspired the researchers to use
the above-mentioned Schiff bases in preparing new complexes [16,17]. Tetrazoles have also
been used by several groups in forming bridges the nickel(II) centers [18-20]. The application of
tetrazole functional groups in medicinal chemistry as a metabolically stable surrogate for a
carboxylic acid group [21-23] and in material science as high density energy materials [24-26]
and also in coordination chemistry as ligands with versatile coordination ability through its four
nitrogen atoms [27,28] are well established. However, the use of Schiff bases as blocking ligands
in preparing tetrazolato bridged di and polynuclear transition metal complexes is very rare. In
our previous papers, we have reported three such complexes of nickel(II) [29,30]. Synthesis of
2

few more nickel(II) complexes was also reported by a different group [31,32]. Two different
methods were used in preparing the complexes. In the first case, the nickel(II) Schiff base
complex with azide co-ligands were isolated in solid state followed by the reaction of this azide
complex with 2-cyanopyridine to prepare the tetrazolato bridged dinuclear nickel(II) complexes
with Schiff base blocking ligand. In the second case, the azide complex was not isolated, instead
tandem synthesis of the tetrazolato bridged nickel(II) Schiff base complexes was reported. In the
present work, we have used two different Schiff bases as blocking ligands and substituted
tetrazolate to prepare two bis(µ-tetrazolato-NN′) bridged dinuclear nickel(II) complexes by
tandem synthesis using 2-cyanopyrazine, sodium azide, nickel(II) acetate and respective Schiff
base ligand under stirring condition in methanol. Our intension was to examine the variation in
molecular architectures, if any, on changing the denticity of the Schiff bases.
We would also like to investigate the variation of the supramolecular architectures of the
complexes. Supramolecular systems based on coordination complexes have received much
attention now-a-days because of their potential use in photonic devices, catalysis, host-guest
chemistry etc. [33,34]. A significant number of supramolecular metal complexes have been
synthesized in the last several years [35,36]. The components of a supramolecule are held
together by a variety of non-covalent forces, e.g. hydrogen bonding, π···π, C-H···π, etc. [37-40].
Herein, we report the tandem synthesis, structural features, spectroscopic characterization and
supra-molecular architectures of two new bis(µ-tetrazolato-NN′) bridged nickel(II) complexes
with N2O donor Schiff base blocking ligands.
2. Experimental Section
3

2.1. Materials
All starting materials were commercially available, reagent grade, and used as purchased
from Sigma-Aldrich without further purification.
2.2. Preparations
2.2.1. Complex [Ni2L1 (PTZ)2]·2(CH3)2SO·2.69H2O (1)
2
A methanol solution (20 ml) of N,N-dimethyl-1,2-diaminoethane (1 mmol, 0.1 ml) and
salicylaldehyde (1 mmol, 0.1 ml) was refluxed for ca. 1 h to produce the ligand 2-((2-
(dimethylamino)ethylimino)methyl)phenol (HL1). Then methanol solution (5 ml) of nickel(II)
acetate tetrahydrate (1 mmol, 250 mg) followed by methanol solution (5 ml) of 2-cyanopyrazine
(1 mmol, 110 mg) was added in stirring condition. A methanol-DMSO (2:1 mixture) solution (15
ml) of sodium azide (1 mmol, 70 mg) was then added and stirred further for ca. 1 h. X-ray
quality single crystals were obtained after several weeks on slow evaporation of the mother
liquor in a refrigerator. Yield: 360 mg (72%, based on nickel). Anal. Calc. for
C36H53.38N16Ni2O6.69S2 (998.86): C, 43.29; H, 5.39; N, 24.40%. Found: C, 43.6; H, 5.7; N, 24.7%.
FT-IR (KBr, cm-1): 3442 (OH), 1641 (C=N), 1452, 1415 (tetrazolate). UV–Vis, λmax (nm)
[εmax(L mol-1 cm-1)] (DMSO): 379 (9037), 555 (51), 725 (101), 912 (151).
2.2.2. Complex 2[Ni2L2 (PTZ)2]·3H2O (2)
2
A methanol solution (20 ml) of N-methyl-1,2-diaminoethane (1 mmol, 0.09 ml) and 3-
methoxysalicylaldehyde (1 mmol, 153 mg) was refluxed for ca. 1 h to produce the ligand 2-((2-
(methylamino)ethylimino)methyl)-6-methoxyphenol (HL2). After then same procedure had been
performed as 1. Single crystals Suitable for X-ray diffraction were obtained after several weeks
on slow evaporation of the mother liquor in a refrigerator. Yield: 310 mg (73%, based on nickel).
4

Anal. Calc. for C64H78N32Ni4O11 (1706.42): C, 45.05; H, 4.61; N, 26.27%. Found: C, 45.2; H,
4.5; N, 26.4%. FT-IR (KBr, cm-1): 3436 (OH), 3260 (NH), 1646 (C=N), 1445, 1413 (tetrazolate).
UV–Vis, λmax (nm) [εmax(L mol-1 cm-1)] (DMSO): 386 (20567), 549 (62), 774 (162), 859 (207).
2.3. Physical measurements
Elemental analysis was performed using a PerkinElmer 240C elemental analyzer. IR
spectra in KBr (4500–500 cm-1) were recorded using a PerkinElmer Spectrum Two FT-IR
spectrophotometer. Electronic spectra in DMSO (1000–300 nm) were recorded in a PerkinElmer
LAMBDA 35 UV/Vis spectrophotometer. Fluorescence spectra were obtained on SHIMADZU
RF-5301PC spectrofluorophotometer at room temperature. Lifetime measurements were
recorded using Hamamatsu MCP photomultiplier (R3809) and were analyzed by using
IBHDAS6 software. Intensity decay profiles were fitted to the sum-of exponentials series
ꢀ(ꢁ) = ꢂ ꢃ ꢅꢆꢇ(−ꢁ/ꢈ )
ꢄ
ꢄ
ꢉ
where Ai is a factor representing the fractional contribution to the time-resolved decay of
the component with a lifetime of τi. The intensity-averaged life times (τav) are determined using
the following equation:
2
< ꢈ >ꢊ= ꢂ ꢃ ꢈ /ꢂ ꢃ ꢈ
ꢄ ꢄ ꢄ ꢄ
ꢉ
ꢉ
2.4. Crystal data collection and refinement
A single crystal having suitable dimensions of both complexes were used for the X-ray
crystallographic analysis. A ‘Bruker D8 QUEST’ diffractometer equipped with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 100 K has been used for data collection of
5

1. A ‘Bruker SMART APEX II’ diffractometer equipped with graphite-monochromated Mo-Kα
radiation (λ=0.71073 Å) at 293 K has been used for 2. In both cases, the molecular structures
were solved by direct methods and refinement by full-matrix least squares on F2 using the
SHELX-97 package [41]. Non-hydrogen atoms were refined with anisotropic thermal
parameters. Hydrogen atoms were placed in their geometrically idealized positions and
constrained to ride on their parent atoms. Hydrogen atoms of water molecules were located by
difference Fourier maps and were kept fixed. Multi-scan empirical absorption corrections were
applied to the data of 2 using the program SADABS [42]. Significant crystallographic data are
summarized in Table 1.
3. Results and Discussions
3.1. Synthesis
In current investigation, we use one tridentate Schiff base (HL1) and a tetradentate one
(HL2) as blocking ligands to prepare tetrazolato bridged nickel(II) complexes. HL1 is prepared by
the condensation of salicylaldehyde with N,N-dimethyl-1,2-diaminoethane whereas, HL2 is
prepared by refluxing 3-methoxysalicylaldehyde with N-methyl-1,2-diaminoethane in methanol
following the literature methods [29,31]. The ligands are not isolated and used for the
preparation of nickel(II) complexes. On the other hand, the tetrazolates are prepared in situ by
1,3-dipolar cycloaddition of cyanide and azide [32]. Our intension is to judge the change in the
molecular architecture of the tetrazolato bridged complexes with the variation in the denticity of
the Schiff bases blocking ligand.
Both the complexes are prepared in situ by the reaction of nickel(II) acetate tetrahydrate,
2-cyanopyrazine and sodium azide with the corresponding Schiff base (HL1 for 1 and HL2 for 2)
6

under stirring condition using methanol-DMSO mixture (2:1) as solvent. In both cases, bis(µ-
tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes are resulted. The molecular
structures of both the complexes are very similar. Thus the denticity of the Schiff base blocking
ligands do not have any effect in the molecular structures of tetrazolato bridged nickel(II)
complexes.
Scheme 1: Synthetic route for preparation of complexes 1 and 2.
7

3.2. Structure descriptions
3.2.1. Complex [Ni2L1 (PTZ)2]·2(CH3)2SO·2.69H2O (1)
2
Complex 1 crystallizes in orthorhombic space group Pbca and features a
centrosymmetric bis(µ-tetrazolato-NN′) bridged dinuclear nickel(II) moiety with two dimethyl
sulphoxide and four lattice water molecules. Two of the lattice water molecules present in the
unit cell, has been refined with occupancy of 0.344(8) per molecules. A perspective view of the
complex with selective atom numbering scheme is shown in Figure 1. Selected bond lengths and
bond angels are given in Table S1. Within the dinuclear unit, each nickel(II) center is six-
coordinated and assumes distorted octahedral geometry. Ni(1) is coordinated by an oxygen atom,
O(1), and two nitrogen atoms, N(1) and N(4), of a deprotonated Schiff base ligand in meridional
fashion and two nitrogen atoms, N(14) and N(21), of deprotonated 5-pyrazinyltetrazolate. A
nitrogen atom, N(22)*, from a symmetry related (1−x,1−y,1−z) deprotonated 5-
pyrazinyltetrazolate of the centrosymmetric dimer coordinates Ni(1) to complete its distorted
octahedral geometry. It should be noted that the (µ-NN′) bridging geometry of the deprotonated
5-pyrazinyltetrazolate is considerably asymmetric, which can be seen from the inequality in the
bridging angles (Ni(1)–N(21)–N(22) = 141.9(2)° and Ni(1)*–N(22)–N(21) = 125.1(2)°) as was
also observed in similar complex [29]. The saturated five membered ring [Ni(1)–N(1)–C(2)–
C(3)–N(4)] has an envelope conformation on C(2) with puckering parameters Q(2) = 0.425(4) Å
and ϕ(2) = 78.4(4)° [43].
There are four hydrogen atoms, H(3C), H(3D), H(4A) and H(4B), available for hydrogen
bonding interactions from two water molecules present in asymmetric unit. Hydrogen atoms,
H(3C) and H(4B), of two water molecules show two different hydrogen bonding interactions
with oxygen atom, O(2), of dimethyl sulphoxide molecule. Another hydrogen atom, H(3D),
8

available from one of those two water molecule is hydrogen bonded with phenoxo oxygen atom,
O(1), of deprotonated Schiff base ligand creating a discrete chain as shown in Figure 2. The
detail geometric features of hydrogen bonding interactions are given in Table 2.
The complex also shows significant C–H···π interactions. One N-methyl hydrogen,
H(12A), attached with C(12) of deprotonated Schiff base ligand and another methyl hydrogen,
H(26C), attached with C(26) of solvent molecule DMSO show two C–H···π interactions with
tetrazole ring Cg(3) and pyrazine ring Cg(6) respectively, of a neighboring deprotonated 5-
pyrazinyltetrazolate. A methylene hydrogen, H(13A) attached with C(13) of deprotonated Schiff
base ligand is involved in C–H···π interactions with the phenyl ring Cg(7) of neighboring
deprotonated Schiff base ligand. Considering the centrosymmetric dimer each of these
interactions is duplicated and produce two dimensional layer structure in the crystal packing of 1
(Figure S1). Geometric features of the C–H···π interactions are given in Table 3.
3.2.2. Complex 2[Ni2L2 (PTZ)2]·3H2O (2)
2
ꢋ
Complex 2 crystallizes in the triclinic space group P1. The asymmetric unit consists of
two bis(µ-tetrazolato-NN′) bridged dinuclear nickel(II) moieties with three noncoordinated water
molecules. A perspective view of one dinuclear unit with selective atom numbering scheme is
shown in Figure 3. Selected bond lengths and bond angels are given in Tables S2 and S3
respectively. Within that dinuclear unit, nickel(II) is coordinated meredonially by one phenoxy
oxygen atom and two nitrogen atoms [O(1), N(1) and N(2) for Ni(1) and O(3), N(9) and N(10)
for Ni(2)] of one depronated Schiff base ligand, along with two nitrogen atoms [N(3) and N(7)
for Ni(1); N(11) and N(15) for Ni(2)] of deprotonated 5-pyrazinyltetrazolate. The sixth
coordination site of each nickel(II) is occupied by a nitrogen atom [N(12) for Ni(1) and N(4) for
9

Ni(2)] of another deprotonated 5-pyrazinyltetrazolate bonded to second nickel atom, constructing
a bis(µ-tetrazolato-NN′) bridged nickel(II) complex. It should be noted that the (µ-NN′) bridging
geometry of the deprotonated 5-pyrazinyltetrazolate is considerably asymmetric, which can be
seen from the inequality in the bridging angles (Ni(1)–N(3)–N(4) = 140.1(2)°, Ni(2)–N(4)–N(3)
= 122.7(2)° and Ni(2)–N(11)–N(12) = 139.2(2)°, Ni(1)–N(12)–N(11) = 124.01(19)°) as was also
observed in similar complex [30]. The saturated five membered ring, Ni(1)–N(1)–C(8)–C(9)–
N(2), has twisted geometry over C(8)–C(9) with puckering parameters Q(2) = 0.421(3) Å and
φ(2) = 97.9(3)°, whereas Ni(2)–N(9)–C(24)–C(25)–N(10) ring has an envelope conformation on
C(25) with puckering parameters Q(2) = 0.432(3) Å and φ(2) = 284.3(3)° [43].
There are three hydrogen atoms, H(2), H(10) and H(26), available from two dinuclear
complexes and six hydrogen atoms, H(9D), H(9E), H(10D), H(10E), H(11D) and H(11E),
available from three water molecules creates a supramolecular tetramer of dinuclear units
through hydrogen bonding interactions (Figure 4). The hydrogen atoms, H(2) and H(10), of one
dinuclear unit, show hydrogen boding interactions with water and phenoxy oxygen atoms, O(9)
and O(1), respectively. Then two hydrogen atoms, H(9C) and H(9D), attached to water oxygen
atom, O(9), show two hydrogen bonding interactions with two other oxygen atoms, O(3)
(phenoxy) and O(4) (methoxy) respectively. The combination of these hydrogen bonding
interactions resulted a supramolecular species as shown in Figure 5A. The hydrogen atom,
H(26), of second dinuclear unit shows hydrogen bonding with water oxygen atom, O(10) and
hydrogen atom, H(10E), attached to O(10) then creates hydrogen bonding with phenoxy oxygen,
O(5) of the same dinuclear unit. Two hydrogen atoms, H(11D) and H(11E), attached to water
oxygen atom, O(11), show two hydrogen bonding interactions with water oxygen atoms, O(10)
and tetrazole nitrogen atom, N(22)†, of a symmetry related († = 3-x,-y,3-z) dinuclear unit
10

respectively creating a centrosymmetric tetranuclear species as shown in Figure 5B. Another
hydrogen atom, H(10D) attached to water oxygen atom O(10), available from centrosymmetric
tetranuclear species shows hydrogen bonding with pyrazine nitrogen atoms, N(8)#, of symmetry
related (# = 3-x,-y,2-z) dinuclear unit. Considering the centrosymmetric tetranuclear unit this
interaction is duplicated and produces a supramolecular tetramer of dinuclear units (Figure 4).
The details of hydrogen bonding interactions are given in Table 2.
There are two significant π⋯π stacking interactions present in the complex. First π⋯π
stacking has been observed between two pyrazine ring Cg(11) and Cg(24) attached with Ni(2)
and Ni(4) respectively of two dinuclear nickel(II) moiety present within the asymmetric unit.
Again one pyrazine ring Cg(10) attached with Ni(1) shows the second π⋯π stacking with
another pyrazine ring Cg(23) attached with Ni(3) of a symmetry related dinuclear moiety. These
two π⋯π stacking creates a one dimensional chain structure of 2 (Figure S2). Complex shows
five significant C–H⋯π interactions. Hydrogen atoms, H(43B) and H(59A), attached with
methoxy carbon atoms, C(43) and C(59), of two depronated Schiff base ligands in one dinuclear
moiety are involved in C–H⋯π interactions with the phenyl rings Cg(26) and Cg(25)
respectively. Another two hydrogen atoms, H(16) and H(32), attached with carbon atoms, C(16)
and C(32) of two (PTZ)− present in another dinuclear moiety are involved in C–H⋯π
interactions with the phenyl rings Cg(25) and Cg(26) respectively. Combination of these four C–
H⋯π interactions produce a two dimensional layer structure as shown in Figure S3. The fifth C–
H⋯π interactions has been observed between two layers involving a hydrogen, H(27B), attached
with methoxy carbon atom, C(27), and phenyl ring Cg(13) creating a double layer structure
(Figure S4). Geometric features of the C–H⋯π and π⋯π stacking are given in Tables 3 and 4
respectively.
11

3.3. IR and electronic spectra and photo-physical study
The infrared spectra of both complexes are quite similar to each other. The distinct band
due to azomethine (C=N) group at 1641 and 1646 cm-1 are noticed in IR spectra of 1 and 2
respectively [44]. Broad band around at 3442 cm-1 and 3436 cm-1 has been noticed indicating the
presence of water molecule in complex 1 and 2 respectively [45]. The sharp band due to the
amino NH group appears at 3260 cm–1 in the spectrum of complex 2 [46].
The electronic spectra of the complexes are similar to each other in DMSO at room
temperature and display absorption bands within the range of 549–555 nm and 859–912 nm with
a shoulder band in the region 725–774 nm. These bands are assigned to the spin allowed
3
3
3
transitions A2g→3T1g(F), A2g→3T2g(P) and spin forbidden transition A2g→1Eg (shoulder
3
band) respectively [29]. The higher energy d–d transitions, corresponding to A2g→3T1g(P) are
obscured by strong ligand to metal charge transfer transitions at 379 nm (for 1) and 386 nm (for
2), which are characteristic of transition metal complexes with Schiff base ligands [30].
The emission spectral behavior of complexes 1 and 2 has also been studied at room
temperature in DMSO solution. The complexes 1 and 2 on excitation at 300 nm shows emissions
at 419 nm and 422 nm with exited state mean lifetimes 5.467 ns and 1.642 ns respectively at
1
room temperature. It can be attributed to intra-ligand fluorescent (π→π*) emissions of the
coordinated ligand [47]. The photoluminescence lifetime spectra and time-resolved
photoluminescence decays have been depicted in Figure 6 and 7 for complexes 1 and 2
respectively.
3.4. Electrochemical studies
12

The redox properties of complexes 1 and 2 were explored by cyclic voltammetry (see
Experimental for details). Both the complexes show one oxidative quasi reversible Ni(III)/Ni(II)
couple at E1/2 = 0.79 V (for 1) and 0.77 V (for 2) (vs. Ag/AgCl) which corresponds to the first
electron abstraction from the corresponding complex. The reductive quasi reversible Ni(II)/Ni(I)
couple at E1/2 = −0.62 V (for 1) and -0.63 V (for 2) can be assigned to the electron addition to
Ni(II) compound to form Ni(I) species. It has been observed that no well defined oxidative or
reductive responses could be observed on running further in the positive or negative potential.
The single-electron nature of the voltammograms has been confirmed by the comparison of
current heights for the compounds and that of a simple [Fe(bipy)3]2+ compound under identical
conditions [48]. The criteria of reversibility were checked by observing constancy of peak–peak
separation (∆Ep = Epa - Epc) and the ratio of peak heights (ipa/ipc~1) with variation of scan rates
[49]. The results of cyclic voltammetry also closely resemble that of the similar reported
compounds, which serve as further evidences for similar structural and electronic properties [30].
All the redox signals remain virtually invariant under different scan rates (0.01–1.0 Vs−1) in the
temperature range 300–280 K. Solvent dependent shift and change in electrochemical
reversibility of red-ox couples are not noteworthy.
4. Summary
The whole work can be concluded in two statements. Firstly, the synthesis of two new
bis(µ-tetrazolato-NN′) bridged dinuclear nickel(II) Schiff base complexes under non-
hydrothermal and non-microwave reaction conditions using a simple in situ 1,3-dipolar cyclo-
addition and their characterization by physico-chemical and structural studies afford a
convenient synthetic route for these types of complexes at room temperature and opens up new
13

possibilities for the syntheses of tetrazolato bridged transition metal complexes with Schiff bases
as blocking ligands. This is particularly important because, although pseudohalide bridged di and
polynuclear transition metal complexes are frequently found in literature, tetrazolato bridged
complexes with Schiff base co-ligands are limited. Secondly, the change in the denticity of the
Schiff base blocking ligand was shown to have no effect in controlling the molecular structure of
such complexes.
Acknowledgment
SC acknowledges DST, India under FAST Track Scheme (Order No. SR/FT/CS-
118/2010, dated 15/02/2012). K.R. gratefully acknowledges the financial support from the
Academy of Finland (project No’s. 122350. 140718, 256259, 265328 and 263256).
Appendix A. Supplementary data
CCDC 1021604 and 1021611 contains the supplementary crystallographic data for
complexes 1 and 2 respectively. The data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-
mail:deposit@ccdc.cam.ac.uk.
14

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18

Table 1: Crystal data and refinement details in complexes 1 and 2
Complex
Formula
1
C36H53.38N16Ni2O6.69S2
998.86
2
C64H78N32Ni4O11
1706.42
Formula Weight
Crystal Size [mm]
Temperature (K)
Crystal system
Space group
a(Å)
0.13 x 0.10 x 0.09
100(2)
0.21 x 0.25 x 0.28
123
Orthorhombic
Pbca
Triclinic
ꢋ
P1
15.120(2)
13.454(2)
21.715(2)
90
11.6034(2)
19.7734(4)
20.2261(4)
118.240(2)
99.2964(17)
95.7235(17)
2
b(Å)
c(Å)
α (°)
β (°)
90
γ (°)
90
Z
4
dcalc (g cm-3)
µ(mm-1)
1.502
1.434
1.013
1.707
F(000)
2092
1772
Total Reflections
Unique Reflections
Observed data [I > 2 σ (I)]
R(int)
20047
25366
4108
14171
2781
12322
0.0874
0.025
R1, wR2 (all data)
R1, wR2 [I > 2 σ (I)]
Largest diff. in peak and hole (eÅ-3)
0.0844, 0.1134
0.0449, 0.0985
0.688, -0.601
0.0518, 0.1322
0.0461, 0.1277
2.16, -1.37
19

Table 2: Hydrogen bond distances (Å) and angles (º) for complexes 1 and 2.
Complexes
D–H···A
D–H
D···A
H···A
2.09(4)
1.92(5)
2.18(2)
2.1800
2.02(5)
2.54(5)
2.3100
2.5100
2.37(6)
1.88(6)
2.08(5)
1.85(6)
2.2200
∠D–H···A
159(5)
164(5)
139(5)
171
O(3)–H(3C)···O(2)
O(3)–H(3D)···O(1)
O(4)–H(4B)···O(2)
N(2)–H(2)···O(9)
0.82(5)
0.84(5)
0.87(5)
0.9300
0.90(5)
0.67(6)
0.9300
0.9300
0.74(5)
0.91(6)
0.84(5)
1.02(6)
0.9300
2.869(5)
2.738(4)
2.89(1)
1
3.105(3)
2.891(3)
3.025(3)
3.221(3)
3.126(3)
3.036(4)
2.776(4)
2.917(3)
2.820(4)
3.088(3)
O(9)–H(9C)···O(3)
O(9)–H(9D)···O(4)
N(10)–H(10)···O(1)
N(10)–H(10)···O(2)
O(10)–H(10D)···N(8)#
O(10)–H(10E)···O(5)
O(11)–H(11D)···N(22)†
O(11)–H(11E)···O(10)
N(26)–H(26)···O(10)
164(5)
132(6)
165
124
2
151(6)
167(4)
175(4)
158(5)
155
Symmetry transformations, # = 3-x,-y,2-z; † = 3-x,-y,3-z for complex 2.
20

Table 3: Geometric features (distances in Å and angles in °) of the C–H···π interactions in 1 and 2.
Complex
C–H····Cg(Ring)
H····Cg
2.81
2.69
2.97
2.95
2.69
2.68
2.88
2.68
C–H····Cg
3.638(4)
3.643(5)
3.830(5)
3.770(3)
3.524(4)
3.447(3)
3.566(4)
3.588(3)
C····Cg
143
C(12)–H(12A)···Cg(3)
C(13)–H(13A)···Cg(7)
C(26)–H(26C)···Cg(6)
C(16)–H(16)···Cg(26)$
C(27)–H(27B)···Cg(13)#
C(32)–H(32)···Cg(25)
C(43)–H(43B)···Cg(26)¥
C(59)–H(59A)···Cg(25)§
166
1
147
145
144
139
2
128
155
Cg(3) = Centre of gravity of the ring [N(21)–N(22)–N(23)–N(24)–C(20)], Cg(6) = Centre of gravity of
the ring [N(14)–C(15)–C(16)–N(17)–C(18)–C(19)], Cg(7) = Centre of gravity of the ring [C(6)–C(7)–
C(8)–C(9)–C(10)–C(11)] for 1 and Cg(13) = Centre of gravity of the ring [C(17)–C(18)–C(19)–C(20)–
C(21)–C(22)], Cg(25) = Centre of gravity of the ring [C(33)–C(34)–C(35)–C(36)–C(37)–C(38)], Cg(26)
= Centre of gravity of the ring [C(49)–C(50)–C(51)–C(52)–C(53)–C(54)] for 2. Symmetry
transformations * = 1-x,1-y,1-z; ◊ = -1/2+x,1/2-y,1-z; ‡ = 3/2-x,1/2+y,z; $ = -1+x,y,-1+z; # = 3-x,-
y,2-z; ¥ = -1+x,y,z; § = 1+x,y,z.
21

Table 4: Geometric features (distances in Å and angles in °) of the π···π stacking in 2.
Cg(I)-Cg(J)
Cg(10)-Cg(23)$
Cg(11)-Cg(24)
Cg-Cg
3.872(2)
3.647(2)
α
β
γ
Cg(I)-Perp
3.333(1)
3.144(2)
Cg(J)-Perp
3.835(1)
3.468(1)
24.0(2)
13.4(2)
7.90
30.60
18.00 30.43
Cg(10) = Centre of gravity of the ring [N(7)–C(13)–C(14)–N(8)–C(15)–C(16)], Cg(11) = Centre of
gravity of the ring [N(15)–C(29)–C(30)–N(16)–C(31)–C(32)], Cg(23) = Centre of gravity of the ring
[N(23)–C(61)–C(62)–N(24)–C(63)–C(64)], Cg(24) = Centre of gravity of the ring [[N(31)–C(45)–C(46)–
N(32)–C(47)–C(48)]. Symmetry transformations $ = -1+x,y,-1+z.
22

Figure 1: A perspective view of dimeric nickel(II) structure with selective atom numbering
scheme of complex 1.
23

Figure 2: A perspective view of hydrogen bonded interactions in complex 1.
24

Figure 3: A perspective view of dimeric nickel(II) structure with selective atom numbering
scheme of complex 2.
25

Figure 4: A perspective view of a hydrogen bonded supramolecular tetramer of dinuclear units
in 2. Only the relevant hydrogen atoms are shown for clarity.
26

Figure 5: A perspective view of hydrogen bonded interactions in complex 2.
27

Figure 6: A perspective view of photoluminescence spectrum (left) and time-resolved
photoluminescence decay profile (right) of 1 in DMSO at room temperature.
28

Figure 7: A perspective view of photoluminescence spectrum (left) and time-resolved
photoluminescence decay profile (right) of 2 in DMSO at room temperature.
29