A combined experimental and computational study on supramolecular assemblies in hetero-tetranuclear nickel(II)-cadmium(II) complexes with N2O4-donor compartmental Schiff bases

Article abstract of DOI:10.1039/c6dt02587k

Two new hetero-tetranuclear nickel(ii)/cadmium(ii) complexes, a cubane [(CH₃CO₂)₂Ni₂(L¹)₂Cd₂(NCS)₂] (1) and a linear tetramer [(DMSO)₂NiL²Cd(NCS)

Full text of DOI:10.1039/c6dt02587k

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Roy, A.
Bhattacharyya, A. Frontera, S. Chattopadhyay, S. Purkait and A. Bauza, Dalton Trans., 2016, DOI:
1
0.1039/C6DT02587K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/dalton

Page 1 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
A combined experimental and computational study on
supramolecular assemblies in heteroꢀtetranuclear nickel(II)ꢀ
cadmium(II) complexes with N O donor compartmental Schiff
2
4
bases
a
a
a
b
b,
Sourav Roy , Anik Bhattacharyya , Sourav Purkait , Antonio Bauzá, Antonio Frontera *
a,
and Shouvik Chattopadhyay *
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata ꢀ 700032, India. Tel:
+
913324572147 eꢀmail: shouvik.chem@gmail.com
b
Departamento de Química, Universitat de les Illes Balears, Crta. deValldemossa km 7.5, 07122 Palma,
Baleares, Spain. eꢀmail:toni.frontera@uib.es
Abstract: Two new heteroꢀtetranuclear nickel(II)/cadmium(II) complexes, a cubane
1
2
[
(CH CO ) Ni (L ) Cd (NCS) ] (1) and a linear tetramer [(DMSO) NiL Cd(NCS)(µ ꢀ
3 2 2 2 2 2 2 2 1,3
2
1
SCN)Ni(DMSO)L Cd(NCS) ] (2) {where H L = N,N'ꢀbis(3ꢀmethoxysalicylidene)propaneꢀ1,3ꢀ
2
2
2
diamine and H L = N,N'ꢀbis(3ꢀethoxysalicylidene)propaneꢀ1,3ꢀdiamine are potential octadentate
2
compartmental Schiff bases}, have been synthesized and characterized. The structures of both
complexes have been confirmed by single crystal Xꢀray diffraction studies. Complex 1 contains
Ni Cd O cubane core whereas complex 2 features an end to end thiocyanate bridged tetranuclear
2
2
4
moiety. Complex 1 shows CꢀHꢁꢁꢁHꢀC interactions whereas a unique Sꢁꢁꢁπ interaction is observed
in complex 2. Theoretical studies have been done using several computational tools like NBO
and AIM analyses. Both complexes show photoluminescence in DMSO medium at room
temperature upon the irradiation of ultraviolet light. The life times of excited states are ~27 ns.
1

Dalton Transactions
Page 2 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Keywords: Cadmium(II); Nickel(II); Compartmental Schiff base; Supramolecular; DFT study;
Photoluminescence.
Introduction
The condensation of various diamines and salicylaldehyde gives H Salen type Schiff
2
bases, which are very well known chelating ligands to the synthetic inorganic chemists since
1
long for the preparation of di and polynuclear complexes. The dinegative anionic forms of these
Schiff bases generally act as tetradentate N O donor chelating ligands to produce mononuclear
2
2
2
complexes, which could cleverly be utilised as ligands (metalloꢀligands) to coordinate a second
metal ion exploiting the interesting bridging ability of the phenoxo oxygen atoms, thereby
3
forming multinuclear complexes. Use of 3ꢀalkoxysalicyalaldehyde instead of salicylaldehyde
itself is more beneficial as it produces compartmental octadentate Schiff bases (with inner N O2
2
and outer O cores), which could again be used efficiently to prepare various homo polynuclear
4
4
complexes. These highꢀnuclearity transition and non transition metal complexes have attracted
5
much attention for their unusual physical properties and relevance to biological function in
6
metalloproteins. Among them, phenoxo bridged tetrameric nickel(II) clusters have been
extensively studied in order to explore the relationship between their structural features and the
7
strength of the magnetic exchange interaction between the nickel(II). Reports on the formation
8
of heteronuclear tetramers are relatively less in literature.
Supramolecular interactions have been shown to play an important role in structural
9
biology and supramolecular chemistry. The harmonization of various biological and physicoꢀ
chemical methods is frequently implemented by amalgamation of many nonꢀcovalent
1
0
supramolecular interactions. A good number of familiar, strong, directional nonꢀcovalent
2

Page 3 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
interactions, such as hydrogen bonding and halogen bonding etc. have been used to manage the
1
1
multiꢀcomponent supramolecular assemblies. In addition, πꢁꢁꢁπ stacking, cationꢁꢁꢁπ, C–Hꢁꢁꢁπ,
12
lpꢁꢁꢁπ and anionꢁꢁꢁπ interactions are also extremely significant in this field. They could manage
the structures of bioꢀmolecules e.g. proteins and DNA, several host–guest systems, enzyme–
1
3
substrate binding, etc. They could also participate in crystal engineering, drug–receptor
1
4
interactions, enzyme inhibition, protein folding etc. As a matter of fact, S···π interactions are
1
4d
crucial in the mechanism of sulphide:quinone oxidoreductase.
Their omnipresent role in
diverse fields attracted the theoretical chemists to investigate and understand the nature of these
weak nonꢀcovalent interactions and as a result, the importance of these nonꢀcovalent interactions
1
5
are analyzed by various researchers using combined theoretical and experimental methods.
In the present work, two similar compartmental N O donor Schiff bases have been used
2
4
to prepare two heteroꢀtetranuclear nickel(II)/cadmium(II) complexes, of which one is a cubane
and the second one is a linear teramer with Ni Cd O cores. These are the first examples of any
2
2
4
heteroꢀtetranuclear nickel(II)/cadmium(II) complexes with H salen type Schiff bases. The
2
unconventional supramolecular interactions found in the crystal packing of these complexes are
theoretically analyzed focusing attention to remarkable Sꢁꢁꢁπ interactions and also to the CꢀHꢁꢁꢁHꢀ
C interactions. Herein, we would like to report the synthesis, characterization, Xꢀray crystal
structure, photoluminescence properties and DFT study on supramolecular architectures of two
new heteroꢀtetranuclear nickel(II)/cadmium(II) complexes.
3

Dalton Transactions
Page 4 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Experimental Section
Nickel(II) thiocyanate tetrahydrate was prepared in laboratory following the literature
1
6
method. All other materials were commercially available, reagent grade and used as purchased
from SigmaꢀAldrich without further purification.
Preparations
Preparation of ligands
1
Preparation of H L [N,N'ꢀbis(3ꢀmethoxysalicylidene)propaneꢀ1,3ꢀdiamine]
2
A methanol solution (10 ml) of 3ꢀmethoxysalicylaldehyde (304 mg, 2 mmol) and 1,3ꢀ
diaminopropane (0.13 ml, 1 mmol) was refluxed for ca. 1 h to form the octadentate ligand. The
ligand was not isolated and used directly for the synthesis of the complex 1.
2
Preparation of H L [N,N'ꢀbis(3ꢀethoxysalicylidene)propaneꢀ1,3ꢀdiamine]
2
1
It was prepared in a similar method as that of H L except that 3ꢀethoxysalicylaldehyde
2
(332 mg, 2 mmol) was used instead of 3ꢀmethoxysalicylaldehyde. The ligand was not isolated
and used directly for the synthesis of the complex 2.
Preparation of complexes
1
Preparation of [(CH CO ) Ni (L ) Cd (NCS) ] (1)
3
2 2
2
2
2
2
A methanol (10 ml) solution of cadmium(II) acetate dihydrate (270 mg, 1 mmol) was
1
added to the methanol solution (20 ml) of H L and the resulting solution was stirred for 15 min.
2
A methanol (10 ml) solution of nickel(II) thiocyanate tetrahydrate (250 mg, 1 mmol) was then
4

Page 5 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
added to it. The stirring was continued for about 2 h. Single crystals, suitable for Xꢀray
diffraction, were obtained after 3ꢀ4 days on slow evaporation of the solution in open atmosphere.
Yield: 460 mg (72%); based on nickel(II). Anal. Calc. for C H Cd Ni O S N (FW =
44
46
2
2
12
2
6
ꢀ1
1
257.21): C, 42.04; H, 3.69; N, 6.68; Found: C, 42.02; H, 3.67; N, 6.69%. FTꢀIR (KBr, cm ):
ꢀ1
ꢀ1
4
1
630 (C=N); 2067 (C≡N). UVꢀVIS [λmax(nm)] [εmax(Lmol cm )] (DMSO): 239 (2.55×10 ); 375
3
(
3.4×10 ); 668 (5.86); 901 (13.84).
2
2
Preparation of [(DMSO) NiL Cd(NCS)(µ ꢀSCN)Ni(DMSO)L Cd(NCS) ] (2)
2
1,3
2
2
It was prepared in a similar method as that of complex 1 except that H L was used
2
1
instead of H L . Few drops of DMSO have been added and the resulting solution has been kept
2
for crystallization. Single crystals, suitable for Xꢀray diffraction, were obtained after 3ꢀ4 days on
slow evaporation of the solution in open atmosphere.
Yield: 570 mg (74%); based on nickel(II). Anal. Calc. for C H Cd Ni O S N (FW =
52
66
2
2
11
7
8
ꢀ1
1
545.82): C, 40.40; H, 4.30; N, 7.25; Found: C, 40.38; H, 4.32; N, 7.27%. FTꢀIR (KBr, cm ):
ꢀ1
ꢀ1
1
628 (C=N); 2034, 2068 (C≡N). UVꢀVIS [λmax(nm)] [εmax(Lmol cm )] (DMSO): 236
4
3
(
2.75×10 ); 378 (3.6×10 ); 672 (7.46); 902 (8.64).
Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were performed using a Perkin
ꢀ1
Elmer 240C elemental analyzer. IR spectra in KBr (4500ꢀ500 cm ) were recorded with a Perkin
Elmer Spectrum Two spectrophotometer. Electronic spectra in DMSO were recorded on a Perkin
Elmer Lambda 35 UVꢀvisible spectrophotometer. Steady state photoluminescence spectra in
DMSO were obtained in Shimadzu RFꢀ5301PC spectrofluorometer at room temperature. Time
5

Dalton Transactions
Page 6 of 37
View Article Online
DOI: 10.1039/C6DT02587K
dependent photoluminescence spectra were recorded using Hamamatsu MCP photomultiplier
R3809) and were analyzed by using IBHDAS6 software. Powder Xꢀray diffraction was
(
performed on a Bruker D8 instrument with Cu K radiation. In this process, the complexes were
α
ground with a mortar and pestle to prepare fine powders. The powders were then dispersed with
alcohol onto a zero background holder (ZBH). The alcohol was allowed to evaporate to provide a
nice, even coating of powder adhered to the sample holder.
Xꢀray crystallography
Suitable single crystals of complexes 1 and 2 were used for data collection using a
‘Bruker SMART APEX II’ diffractometer equipped with graphiteꢀmonochromated Mo Kα
radiation (λ= 0.71073 Å) at 100 K. The molecular structures were solved by direct method and
2
17
refined by fullꢀmatrix least squares on F using the SHELXꢀ2014 package. Nonꢀhydrogen
atoms were refined with anisotropic thermal parameters. The hydrogen atoms were placed in
their geometrically idealized positions and constrained to ride on their parent atoms. Multiꢀscan
1
8
empirical absorption corrections were applied to the data using the program SADABS. Details
of crystallographic data and refinement details are given in Table 1.
The crystal structure of complex 1 is somewhat problematic. The unit cell includes some
highly disordered solvent molecules, which could not be modelled as discrete atomic sites. We
employed PLATON/SQUEEZE to calculate the diffraction contribution of the solvent molecules
and thereby produce a set of solventꢀfree diffraction intensities. Details about the SQUEEZE
procedure are given in the CIF file.
Theoretical methods
6

Page 7 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
The calculations of the noncovalent interactions were carried out using the
1
9
TURBOMOLE version 7.0 using the M06ꢀ2X/def2ꢀTZVP level of theory. To evaluate the
interactions in the solid state, we have used the crystallographic coordinates and optimized the
position of the H atoms. In the large assemblies computed for complex 1 the SVP basis set was
used instead of the timeꢀconsuming def2ꢀTZVP basis set. This procedure and level of theory
2
0
have been successfully used to evaluate similar interactions. The interaction energies were
computed by calculating the difference between the energies of isolated monomers and their
assembly. The interaction energies were corrected for the Basis Set Superposition Error (BSSE)
2
1
using the counterpoise method.
2
2
The Natural Bond Orbital (NBO) method has been employed to analyze chargeꢀtransfer
interactions between occupied and empty orbitals using the NBOꢀ3.1 program, included within
the Gaussianꢀ09 program. The Bader’s "Atoms in molecules" theory has been used to study the
2
3
interactions discussed herein by means of the AIMall calculation package.
Results and Discussion
Synthesis
1
,3ꢀdiaminopropane has been refluxed with 3ꢀmethoxysalicylaldehyde and 3ꢀ
1
ethoxysalicylaldehyde respectively to form two potential octadentate Schiff base ligands, H L
2
2
24
1
2
and H L respectively, following the literature method. These Schiff bases (H L and H L ) on
2
2
2
reaction with cadmium(II) acetate dihydrate followed by the addition of nickel(II) thiocyanate
tetrahydrate give two heteronuclear complexes. Formation of both complexes is shown in
Scheme 1.
7

Dalton Transactions
Page 8 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Scheme 1: Preparation of ligands and complexes. Only the cubane core of complex 1 is shown
for clarity.
Description of structures
1
[
(CH CO ) Ni (L ) Cd (NCS) ] (1)
3
2 2
2
2
2
2
The Xꢀray crystal structure determination reveals that complex 1 crystallizes in the
triclinic space group P . The complex contains two independent heteroꢀtetranuclear units (A and
B) with equivalent geometries. Perspective view of unit A is shown in Fig. 1. The cubane core
along with coordinating atoms have been highlighted in Fig. 2. Cubane core of unit B has a
similar structure as shown in Fig. S1 {Electronic supplementary information (ESI)}. Important
bond lengths of unit A are given in Table 2. Important bond lengths of unit B along with bond
angles (unit A and B) are gathered in Tables S1ꢀS3.
8

Page 9 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Fig. 1: Perspective view of complex 1 (unit A). Only the Cd Ni O cubane core have been
2
2
4
labelled. Hydrogen atoms have been omitted for clarity.
Fig. 2: Perspective view of Cd Ni O cubane core of unit A along with coordinating atoms and
2
2
4
bridging acetate ligands.
9

Dalton Transactions
Page 10 of 37
View Article Online
DOI: 10.1039/C6DT02587K
The molecular structure of unit A is built from isolated heteronuclear molecules of
1
1
[
(CH CO ) Ni (L ) Cd (NCS) ], in which both nickel(II) centres are hexacoordinated. H L is a
3 2 2 2 2 2 2 2
potential octadentate compartmental Schiff base with inner N O and outer O compartments.
2
2
4
Nickel(II) centres occupy the inner N O cavities while each cadmium(II) resides in the outer O
4
2
2
compartments. Both nickel(II) centres, Ni(1) and Ni(2), have pseudo octahedral geometries.
Each nickel(II) centre is attached with two imine nitrogen atoms, [N(1) and N(2) for Ni(1); N(3)
and N(4) for Ni(2)] and two phenoxo oxygen atoms, [O(1) and O(2) for Ni(1); O(5) and O(6) for
1
2ꢀ
Ni(2)] of the deprotonated Schiff base (L ) constitute the equatorial plane. The fifth
coordination site of each nickel centre is occupied by another phenoxo oxygen atom, [O(5) for
Ni(1) and O(1) for Ni(2)], from the second deprotonated Schiff base. The octahedral geometries
around both nickel(II) centres are fulfilled by the coordination of two oxygen atoms [O(10) for
Ni(1); which bridges between Ni(1) and Cd(1) whereas O(11) for Ni(2); which bridges between
Ni(2) and Cd(2)] from two bridging acetates. For Ni(1) centre, the deviation of the coordinating
atoms, O(1), O(2), N(1) and N(2) in the basal plane from the mean plane passing through them
are 0.002(6), 0.008(6), 0.008(9), 0.002(8) Å respectively. The deviation of Ni(1) from the same
plane is ꢀ0.020(13) Å. For Ni(2) centre, the deviation of the coordinating atoms O(5), O(6), N(3)
and N(4) in the basal plane from the mean plane passing through them are 0.007(6), ꢀ0.014(6), ꢀ
0.013(9), 0.006(8) Å respectively. The deviation of Ni(2) from the same plane is 0.0146(12) Å.
Each cadmium(II) centre is heptacoordinated. Each cadmium(II) resides in outer O4
compartments being coordinated by two phenoxo [O(1) and O(2) for Cd(1); O(5) and O(6) for
Cd(2)] and two methoxo oxygen atoms [O(3) and O(4) for Cd(1); O(7) and O(8) for Cd(2)]. The
fifth coordination sites in each cadmium(II) is occupied by two terminal Nꢀbonded thiocyanates
[
N(5) for Cd(1) and N(6) for Cd(2)]. Two phenoxo oxygen atoms [O(6) for Cd(1) and O(2) for
10

Page 11 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Cd(2)] coordinate both cadmium(II) centres axially to complete its sixth coordination. The
pentagonal bipyramidal geometry around each cadmium(II) is completed by the coordination of
oxygen atoms [O(9) for Cd(1) and O(12) for Cd(2)] of bridging acetate groups.
Cadmium(II) and nickel(II) centres in the cubane reside in identical environment. Within
the cubane unit Cd(1)ꢀNi(1), Ni(2)ꢀCd(2) and Ni(2)ꢀNi(1) distances are significantly shorter
(~3.32 Å) compared to Cd(1)ꢀNi(2) and Cd(2)ꢀNi(1) distances (~3.44 Å). The Cd(1)ꢀCd(2)
distance is relatively longer (~3.69 Å). The cubane core has six faces. The Cd O face is opposite
2
2
of Ni O face. The bridging angles MꢀOꢀM (M = metal) are comparable (~103°). The saturated
2
2
six membered chelate rings [Ni(1)–N(1)–C(9)–C(10)–C(11)–N(2)] and [Ni(2)–N(3)–C(31)–
C(32)–C(33)–N(4)] have envelope conformations with puckering parameters q = 0.523(14) Å; θ
2
5
=
143.3(12)°; φ = 354(2)° and q = 0.503(13) Å; θ = 144.9(12)°; φ = 2(2)° respectively. The
structure of unit B is similar as that of unit A and described in Electronic supplementary
information (ESI).
Complex 1 shows significant CꢀHꢁꢁꢁπ interactions. The hydrogen atom, H(9B), attached
to carbon atom, C(9), is involved in an intraꢀmolecular CꢀHꢁꢁꢁπ interaction with the phenyl ring
[
C(24)–C(25)–C(26)–C(27)–C(28)–C(29)]. Similarly the hydrogen atom, H(55B), attached to
carbon atom, C(55), is involved in another intraꢀmolecular CꢀHꢁꢁꢁπ interaction with the phenyl
ring [C(68)–C(69)–C(70)–C(71)–C(72)–C(73)]. Another intraꢀmolecular CꢀHꢁꢁꢁπ interaction is
observed between the hydrogen atom, H(75A), attached to carbon atom, C(75), with the phenyl
ring [C(57)–C(58)–C(59)–C(60)–C(61)–C(62)]. The hydrogen atom H(36), attached to carbon
atom, C(36), shows another CꢀHꢁꢁꢁπ interaction with the phenyl ring [C(68)–C(69)–C(70)–
C(71)–C(72)–C(73)]. These CꢀHꢁꢁꢁπ interactions are shown in Fig. S2 {Electronic supplementary
information (ESI)}. The hydrogen atom, H(80), attached to carbon atom, C(80), shows an interꢀ
11

Dalton Transactions
Page 12 of 37
View Article Online
DOI: 10.1039/C6DT02587K
molecular CꢀHꢁꢁꢁπ interaction with a symmetry related (x,1+y,z) phenyl ring [C(2)–C(3)–C(4)–
C(5)–C(6)–C(7)] as shown in Fig. S3. Another CꢀHꢁꢁꢁπ interꢀmolecular interaction is observed
between the hydrogen atom, H(49), attached to carbon atom, C(49), with the symmetry related (ꢀ
1+x,y,z) phenyl ring [C(24)–C(25)–C(26)–C(27)–C(28)–C(29)] shown in Fig. S4. The hydrogen
atom, H(14), attached to carbon atom, C(14), is involved in another interꢀmolecular CꢀHꢁꢁꢁπ
interaction with the symmetry related (1+x,ꢀ1+y,z) phenyl ring [C(57)–C(58)–C(59)–C(60)–
C(61)–C(62)] shown in Fig. S5. The details of the geometric features of the CꢀHꢁꢁꢁπ interactions
are given in Table 3.
2
2
[
(DMSO) NiL Cd(NCS)(µ ꢀSCN)Ni(DMSO)L Cd(NCS) ] (2)
2 1,3 2
The Xꢀray crystal structure determination reveals that complex 2 crystallizes in the
monoclinic space group P2 . The asymmetric unit contains a tetranuclear neutral species,
1
2
2
[
(DMSO) NiL Cd(NCS)(µ ꢀSCN)Ni(DMSO)L Cd(NCS) ] (Fig. 3). Metal centres along with
2 1,3 2
coordinating atoms and bridging thiocyanate is shown in Fig. 4. The tetranuclear moiety consists
2
of two pseudodinuclear units,
C
[Ni(DMSO)L Cd(NCS) ] (Fig. 5a) and
D
2
2
+
[
(DMSO) NiL Cd(NCS)] (Fig. 5b), which are joined through a single end to end thiocyanate
2
bridge. Important bond lengths and bond angles are gathered in Tables 2 and S2 {Electronic
supplementary information (ESI)} respectively. In the dimeric unit C, the Ni(1) and Cd(1)
centres occupy the inner N O and outer O sites, respectively. Ni(1) and Cd(1) centres are
2
2
4
bridged by two phenoxo oxygen atoms, O(1) and O(2), with Ni(1)ꢁꢁꢁCd(1) distance of 3.324(8)
Å. Both Ni(1) and Cd(1) have pseudo octahedral geometries. Ni(1) is coordinated by two imine
nitrogen atoms, N(1) and N(2), two phenoxo oxygen atoms, O(1) and O(2), of one deprotonated
2
2ꢀ
potential octadentate Schiff base ligand (L ) which constitute the equatorial plane. The fifth
coordination site is occupied by one oxygen atom, O(5) from DMSO molecule whereas, the sixth
12

Page 13 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
coordination site of Ni(1) is occupied by a nitrogen atom, N(5), of an end to end bridged
thiocyanate, which links two pseudodinuclear units, C and D. On the other hand, Cd(1) is
coordinated by two phenoxo oxygen atoms, O(1) and O(2), two ethoxy oxygen atoms, O(3) and
O(4) which constitute the equatorial plane. The fifth and sixth coordination site is occupied by
two nitrogen atoms, N(6) and N(7), from two terminal thiocyanates. The bridging angles Ni(1)–
O(1)–Cd(1) and Ni(1)–O(2)–Cd(1) are 102.4(1)° and 103.4(1)° respectively. The angles O(1)–
Ni(1)–O(2) and O(1)–Cd(1)–O(2) are 81.6(1)° and 72.5(1)° respectively. The saturated six
membered chelate ring [Ni(1)–N(1)–C(14)–C(15)–C(16)–N(2)] has envelope conformations
2
5
with puckering parameters q = 0.490(9) Å; θ = 132(8)°; φ = 347.7(11)°.
Fig. 3: Perspective view of complex 2 with selective atom numbering scheme. Hydrogen atoms
have been omitted for clarity.
13

Dalton Transactions
Page 14 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Fig. 4: Perspective view of the tetranuclear unit of complex 2 with selective atom numbering
scheme. Only the metal centres with coordinating atoms along with the bridging thiocyanate
have been shown for clarity.
14

Page 15 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Fig. 5: Perspective views of pseudo dinuclear units [(a) ꢀ unit C; (b) ꢀ unit D] of complex 2 with
selective atom numbering scheme. Hydrogen atoms along with methyl groups of DMSO and
ethyl groups have been omitted for clarity.
The dinuclear unit D has similar structure compared to unit C. Unit D contains nickel(II)
and cadmium(II) centres, Ni(2), Cd(2), which are bridged by two phenoxo oxygen atoms, O(6)
and O(7), with Ni(2)ꢁꢁꢁCd(2) distance of 3.300(6) Å. Ni(2) is coordinated by two imine nitrogen
atoms, N(8) and N(9), and two phenoxo oxygen atoms, O(6) and O(7), of the deprotonated
2
2ꢀ
potential octadentate Schiff base ligand (L ) . Remaining two coordination sites of Ni(2) are
occupied by two oxygen atoms, O(10) and O(11), from two DMSO molecules. On the other
hand, Cd(2) is coordinated by two phenoxo oxygen atoms, O(6) and O(7), two ethoxy oxygen
atoms, O(8) and O(9), and one nitrogen atoms N(10) from one terminal thiocyanate. The sixth
coordination site of Cd(2) is occupied by a sulphur atom, S(7) of an end to end bridged
thiocyanate which links two pseudodinuclear units, C and D. The saturated six membered
chelate ring [Ni(2)–N(8)–C(35)–C(36)–C(37)–N(9)] has envelope conformations with puckering
2
5
parameters q = 0.528(6) Å; θ = 144.1(5)°; φ = 3.5(10)°. The Ni(1)ꢁꢁꢁCd(2) separation in the
tetranuclear unit is ~6.42 Å.
Complex 2 shows three CꢀHꢁꢁꢁπ interactions. The hydrogen atom, H(48A), attached to
carbon atom, C(48), is involved in an interꢀmolecular (between two C units) CꢀHꢁꢁꢁπ interaction
with a symmetry related (ꢀx,2ꢀy,ꢀz) phenyl ring [C(18)–C(19)–C(20)–C(21)–C(22)–C(23)] to
form a supraꢀmolecular dimer. One intraꢀmolecular CꢀHꢁꢁꢁπ interaction is observed between two
different subunits of the complex having different symmetries. The hydrogen atom, H(29),
attached to carbon atom, C(29), is involved in an intraꢀmolecular (between C and D units) Cꢀ
Hꢁꢁꢁπ interaction with the phenyl ring [C(7)–C(8)–C(9)–C(10)–C(11)–C(12). These interactions
15

Dalton Transactions
Page 16 of 37
View Article Online
DOI: 10.1039/C6DT02587K
are shown in Fig. S6 {Electronic supplementary information (ESI)}. The hydrogen atom, H(41),
attached to carbon atom, C(41), is involved in another interꢀmolecular (between C and D units)
CꢀHꢁꢁꢁπ interaction with the symmetry related (1/2+x,3/2ꢀy,1/2+z) phenyl ring [C(7)–C(8)–C(9)–
C(10)–C(11)–C(12)] to form another supraꢀmolecular dimer shown in Fig. S7. The details of the
geometric features of the CꢀHꢁꢁꢁπ interactions are given in Table 3. In addition to these CꢀHꢁꢁꢁπ
interactions complex 2 also shows Sꢁꢁꢁπ interaction. The remarkable Sꢁꢁꢁπ interaction is observed
between the lone pair of disordered sulphur atom with the CꢀN and CꢀS orbitals of the
thiocyanate [N(7)ꢀC(2)ꢀS(9)] attached with Cd(1). In this Sꢁꢁꢁπ interaction, DMSO is acting as
electron rich moiety (electron donor) while thiocyanate acts as electron acceptor one in spite of
its anionic character. Details of this Sꢁꢁꢁπ interaction has been explored under theoretical study
part.
Theoretical study
We have divided the theoretical study into two parts. First we have rationalized the
surprisingly different architecture observed in the solid state of two complexes, taking into
account that the only difference between the H salen type Schiff bases is the alkoxy substituent
2
(methoxy or ethoxy). Second, we have analysed the supramolecular assemblies observed in the
crystal packing of complexes 1 and 2.
As described above, in the cubane assembly, each cadmium(II) centre is
heptacoordinated being coordinated by two phenoxo and two methoxo oxygen atoms. The fifth
coordination site in the equatorial plane is occupied by a terminal Nꢀbonded thiocyanate. This
coordination mode that is required for the formation of the cubane is only possible for the
methoxy substituted ligand, since the steric hindrance of both ethoxy groups prevents the
2
formation of the heptacoordinated cadmium atom (only four atoms in the equatorial plane) in L
16

Page 17 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
ligand (Fig. 6). As a matter of fact, the cadmium ions are hexacoordinated in compound 2 giving
rise to a totally different complex.
1
2
Fig. 6: CPK representation of the nickel(II)/cadmium(II) complexes with L (a) and L (b).
In the crystal structure of 2, the nickel(II) and cadmium(II) metal centers are bridged by
only one NCS ligand, in which the nickel(II) of the unit C is connected with the cadmium(II) of
the unit D through the NCS bridge. On the other hand, the nickel(II) of the unit D is not
coordinated by the NCS ligand from the unit C but is coordinated by two DMSO molecules. One
of both DMSO molecules establishes a noncovalent S···π interaction that is studied below. The
coordination of this DMSO molecule prevents the formation of the doubly NCSꢀbridged
structure. We have analysed this issue by means of DFT calculations. We have optimized the
hypothetical double bridge structure and compared the formation energy with the one observed
experimentally. The results are shown in Fig. 7 and it can be observed that the dissymmetric
assembly observed experimentally is 14.4 kcal/mol more stable that the doubly bridged structure.
A likely explanation is that both assemblies present the same number of metalꢀligand
coordination bonds but the experimentally observed complex has some additional stabilization
from the intramolecular noncovalent interactions established by the DMSO molecule.
17

Dalton Transactions
Page 18 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Fig. 7: Optimized geometries of the dissymmetric assembly of complex 2 (left) and the
hypothetical doubly bridged assembly. The formation energy is also indicated.
The second part of the theoretical study is devoted to analyze the unconventional
noncovalent interactions found in the crystal packing of complexes 1 and 2 focusing our
attention to CꢀHꢁꢁꢁHꢀC interactions and the remarkable Sꢁꢁꢁπ interactions. In 1 we have analyzed
the interesting CꢀHꢁꢁꢁHꢀC interactions observed between the organic ligand and acetate coligand
in the solid state structure. In 2 we have analyzed the remarkable and unprecedented Sꢁꢁꢁπ
interaction observed in the solid state structure by using several computational tools like NBO
and AIM analyses. The importance of CꢀHꢁꢁꢁHꢀC interaction has been highlighted by Alvarez
2
6
and coworkers. Dihydrogen contacts in alkanes are among the weakest intermolecular
interactions (∼ꢀ0.4 kcal/mol for methane dimer), however they are cumulative resulting in larger
dimerization energies in some cases (e.g. long open chains). For example the complexation
2
6
energy computed for the dimer of nꢀhexane is ꢀ4.5 kcal/mol.
It is also worthy to emphasize that supramolecular chemists usually analyze the
conventional noncovalent interactions in the Xꢀray structures (shorter than the sum of van der
18

Page 19 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Waals radii) ignoring longer interactions in the crystal structures. Evidently, this is a simplistic
view of crystal packing since interactions slightly longer also have an impact. Bearing this in
mind, we have studied the interesting crystal packing observed in 1 (Fig. 8a) where 2D planes
are found in the solid state governed basically by long range dispersion and CꢀHꢁꢁꢁHꢀC
interactions. Curiously the tetranuclear complexes are arranged in such a way that four methyl
groups belonging to the acetate ligands of four different complexes are pointing to the same void
space (Fig. 8a). In a similar way, for methyl groups of the methoxy substituent of the aromatic
ligand are also pointing to a void space of the 2D plane (blue lines in Fig. 8a). Moreover, the
formation of the 2D plane is due to van der Waals dispersion interactions between the bulk of the
molecules. In order to evaluate the contribution of the CꢀHꢁꢁꢁHꢀC interactions involving the
methyl groups, we have used a theoretical model that consists of one dimer taken from this 2D
plane, Fig. 8b (using the crystallographic coordinates). We have computed its interaction energy,
which is ꢂE = ꢀ22.7 kcal/mol that can be attributed to the contribution of two CH ꢁꢁꢁH C
1
3
3
interactions (in one the –CH groups are from the acetate and in the other from the methoxy
3
group, see dashed lines) along with long range interactions. In an effort to estimate the
contribution of the CꢀHꢁꢁꢁHꢀC interaction, we have computed an additional model where the
methyl groups have been changed by hydrogen atoms (small arrows in Fig. 8c). As a result the
interaction is modestly reduced to ꢂE = ꢀ21.7 kcal/mol that is the contribution of the van der
2
Waals dispersion interactions between the bulk of the two molecules. The difference between
both interaction energies (ꢂE ꢀ ꢂE = ꢀ1 kcal/mol) is the contribution of the CH ꢁꢁꢁH C
1
2
3
3
interactions. This value is in good agreement with reported calculations of the methane dimer.
19

Dalton Transactions
Page 20 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Fig. 8: (a) Partial view of the Xꢀray solid state structure of 1, Hꢀatoms have been omitted for
clarity. Some –CH groups are highlighted using higher ball radius in the ball & stick
3
representation; (b,c) Theoretical models used to evaluate the C–H···H–C interaction. Only the
Hꢀatoms of the interacting methyl groups are shown. Distances in Å.
In complex 2 we have analyzed the disordered DMSO molecule observed in its solid state
Xꢀray structure (Fig. 9a). The sulphur atom is disordered in two positions and in one of both the
sulphur atom is in contact with the central carbon atom of the bridging thiocyanate. This
interaction can be viewed as a contact between the electron rich sulphur atom with the πꢀsystem
2
7
of the thiocyanate. In fact we have previously demonstrated the ability of pseudohalide ligands
(thiocyanate and selenocyanate) to interact with either Hꢀbond (via the ending atoms) or lone
pair donors (via the central carbon atom). We have evaluated energetically the difference
between the two disordered positions at the M06ꢀ2X/def2ꢀTZVP level of theory and the one with
the Sꢁꢁꢁπ interaction is more stable in 3 kcal/mol that can be attributed to this interaction.
20

Page 21 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Fig. 9: (a) Xꢀray solid state structure of 2; (b,c) Theoretical models used to evaluate the S···π
interaction. Hꢀatoms omitted for clarity. Distances in Å.
At this point, in order to investigate the S⋯π interaction from an orbital point of view we
have performed Natural Bond Orbital (NBO) calculations in the model of Fig. 9c focusing our
attention on the second order perturbation analysis that is very useful to study donor acceptor
2
8
interactions. Interestingly, we have found that the lone pair (lp orbital) of the sulphur atom of
DMSO interacts with the CꢀN and CꢀS antibonding orbitals (BD*) of the thiocyanate with a
(2)
concomitant second order stabilization energy of E = 0.98 kcal/mol for the LP(S)→BD*(CN)
(2)
interaction and E = 0.05 kcal/mol for the LP(S)→BD*(CS) orbital interaction. Therefore the
global orbital stabilization energy that can be attributed to the Sꢁꢁꢁπ interaction is approximately
1.03 kcal/mol in the dimer (~33% of the total interaction energy). This analysis confirms both
the existence of the interaction and also that the DMSO is acting as electron rich moiety (electron
donor) and the thiocyanate moiety as electron acceptor, in spite of its anionic character. This is
likely due to the double coordination of the thiocyanate to two divalent metal centers [nickel(II)
and cadmium(II)] that drastically increases the πꢀacidity of the ligand. We have also computed
21

Dalton Transactions
Page 22 of 37
View Article Online
DOI: 10.1039/C6DT02587K
the AIM analysis of the model of complex 2 shown in Fig. 9c in order to investigate the
distribution of critical points, which is shown in Fig. 10. It can be observed a bond critical point
and bond path that connect the sulphur atom of the DMSO with the sulphur atom of the
pseudohalide ligand, thus confirming the Sꢁꢁꢁπ interaction. The rest of critical points and bond
paths in this assembly have been omitted for clarity.
Fig. 10: Representation of the bond critical point (red sphere) and bond path connecting the S
atom of DMSO to the S atom of the pseudohalide ligand (dashed line). H atoms omitted for
clarity
IR and electronic spectra and photoꢀphysical study
In the IR spectra of both complexes, distinct bands due to the azomethine (C=N) groups
ꢀ1
29
ꢀ1
within the range of 1626ꢀ1632 cm are routinely noticed. A strong band at 2067 cm indicates
the presence of terminal Nꢀbonded thiocyanate in complex 1. There are two strong bands at 2034
ꢀ1
and 2068 cm in complex 2 indicating the presence of terminal (Nꢀbonded) and end to end
22

Page 23 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
3
0
bridged thiocyanate respectively which are also evident from the crystal structure
determination.
10
As cadmium(II) is a d system, no dꢀd bands are observed due to cadmium(II). The
intense absorption bands at shorter wavelengths (~ 375 nm) may be assigned to metalꢀtoꢀligand
3
1a
charge transfer bands (MLCT) due to both nickel(II) and cadmium(II) centres. In the visible
range, two absorption bands around 670 nm and 900 nm are observed. These bands may be
3
3
3
3
31b,c
assigned as T (F) ← A (F) and T (F) ← A (F) respectively.
The higher energy dꢀd
1
g
2g
2g
2g
3
3
band, T (P) ← A (F), expected for octahedral nickel(II), cannot be observed as it is obscured
1
g
2g
3
1c
by strong charge transfer transitions (~375 nm). The bands ~270 nm may be assigned as ligand
*
32
centred π ← π transitions.
Both complexes exhibit fluorescence in DMSO medium. The fluorescence data are listed
*
in Table 4 (without solvent correction). These are assigned as intraꢀligand (π ← π)
3
2
fluorescence. The mean lifetimes (г ) of the exited states are 27.7 ns (for 1) and 26.8 ns (for
avg
2
) at room temperature (Table 4). Decay profiles (Fig. 11) were fitted to a multiꢀexponential
model:
where, biꢀexponential functions are used to fit the emission of all complexes with and obtaining
2
χ close to 1. The intensityꢀaveraged life times (г ) are determined using the following equation:
avg
23

Dalton Transactions
Page 24 of 37
View Article Online
DOI: 10.1039/C6DT02587K
where, α and τ are the preꢀexponential factor and excitedꢀstate luminescence decay time
i
i
associated with the iꢀth component, respectively.
Fig. 11: Lifetime decay profile of complexes 1 and 2.
PXRD
The experimental PXRD patterns of the bulk products are in good agreement with the
simulated XRD patterns from single crystal Xꢀray diffraction results, indicating consistency of
the bulk sample. The simulated patterns of the complexes were calculated from the single crystal
structural data (Cif) using the CCDC Mercury software.
24

Page 25 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Concluding Remarks
We have synthesized and Xꢀray characterized two new heteroꢀtetranuclear nickel(II)ꢀ
cadmium(II) complexes with a Schiff base ligand. Among them, complex 1 is a phenoxo bridged
cubane and complex 2 is a linear teramer with Ni Cd O cores. The linear tetramer consists of
2
2
4
two pseudodinuclear units, joined through a single end to end thiocyanate bridge. The solid state
structure of complex 1 shows the participation of the organic ligand and acetate group in Cꢀ
HꢁꢁꢁHꢀC interactions that have been evaluated energetically by means of DFT calculations.
Moreover, the disorder of the DMSO molecule has been studied in complex 2 since one of the
disordered DMSO molecule presents an unprecedented Sꢁꢁꢁπ interaction where the πꢀsystem is
provided by the thiocyanate. This unexpected interaction has been evidenced by means of several
computational tools like NBO and AIM analyses.
Acknowledgments
This work was supported by the Jadavpur University Research Grant and the University
Grants Commission, CASꢀUGC, New Delhi. We thank the MINECO of Spain (projects
CTQ2014ꢀ57393ꢀC2ꢀ1ꢀP and CONSOLIDER INGENIO 2010 CSD2010ꢀ00065, FEDER funds).
We thank the CTI (UIB) for computational facilities.
25

Dalton Transactions
Page 26 of 37
View Article Online
DOI: 10.1039/C6DT02587K
Notes and references
CCDC 1445222 and 1445223 contain the supplementary crystallographic data for 1 and 2
respectively.
1
(a) A. Hazari, L. K. Das, A. Bauzá, A. Frontera and A. Ghosh, Dalton Trans., 2016, 45, 5730ꢀ
740; (b) P. Seth, S. Giri and A. Ghosh, Dalton Trans., 2015, 44, 12863ꢀ12870; (c) B.
5
J. Kennedy and K. S. Murray, Inorg. Chem., 1985, 24, 1552ꢀ1557; (d) A. van den Bergen, K. S.
Murray, B. O. West and A. N. Buckley, J. Chem. SOC. (A), 1969, 2051ꢀ2060; (e) E. Uhlig,
Coord. Chem. Rev., 1973, 10, 227ꢀ264; (f) S. Yamada, Coord. Chem. Rev., 1999, 190ꢀ192, 537ꢀ
5
55; (f) P. Mukherjee, C. Biswas, M. G. B. Drew, A. Ghosh, Polyhedron, 2007, 26, 3121ꢀ3128;
g) L. S. Felices, E. C. EscuderoꢀAda´n, J. BenetꢀBuchholz and A. W. Kleij, Inorg. Chem., 2009,
8, 846ꢀ853; (h) S. A. Fairhurst, D. L. Hughes, G. J. Leigh, J. R. Sanders and J. Weisner, J.
Chem. SOC. Dalton Trans., 1994, 2591ꢀ2598; (i) R. M. Clarke and T. Storr, Dalton Trans.,
(
4
2
2
2
014, 43, 9380ꢀ9391; (j) X. Yanga, R. A. Jonesb and S. Huanga, Coord. Chem. Rev., 2014, 273ꢀ
74, 63ꢀ75.
(a) N. Sarkar, P. K. Bhaumik and S. Chattopadhyay, Polyhedron, 2016, 115, 37ꢀ46; (b) P.
Bhowmik, H. P. Nayek, M. Corbella, N. AliagaꢀAlcalde and S. Chattopadhyay, Dalton Trans.,
2011, 40, 7916ꢀ7926; (c) E. L´opezꢀTorres and M. A. Mendiola, Dalton Trans., 2009, 7639ꢀ
7647; (d) M. Sutradhar, T. Roy Barman, M. G.B.Drew and Eva Rentschler, J. Mol. Struct., 2013,
1041, 44ꢀ49; (e) D. A. Rotsch, K. M. Reinig, E. M. Weis, A. B. Taylor, C. L. Barnesa and S. S.
Jurisson; Dalton Trans., 2013, 42, 11614ꢀ11625; (f) S. Chandra and R. Kumar, Transition Met.
Chem., 2004, 29, 269ꢀ275; (g) S. A. Schuetz, C. M. Silvernail, C. D. Incarvito, A. L. Rheingold,
J. L. Clark, V. W. Day and J. A. Belot, Inorg. Chem., 2004, 43, 6203ꢀ6214; (h) S. Mohebbi and
M. Abdi, J. Coord. Chem., 2008, 61, 3410ꢀ3419; (i) A. Ray, S. Banerjee, G. M. Rosair, V.
26

Page 27 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
Gramlich and S. Mitra, Struct. Chem. 2008, 19, 459ꢀ465; (j) D. Mandal, P. B. Chatterjee, S.
Bhattacharya, K.ꢀY. Choi, R. Cle´rac and M. Chaudhury, Inorg. Chem., 2009, 48, 1826ꢀ1835; (k)
A. Vlad, M.ꢀF. Zaltariov, S. Shova, M. Cazacu, M. Avadanei, A. Soroceanu and P. Samoila,
Polyhedron, 2016, 115, 76ꢀ85.
3
(a) S. Bhattacharya and S. Mohanta, Inorg. Chim. Acta, 2015, 432, 169ꢀ175; (b) P.A. Vigato
and S. Tamburini, Coord. Chem. Rev. 2008, 252, 1871ꢀ1995; (c) L. K. Das, C. J. GómezꢀGarcía,
M. G.B. Drew and A. Ghosh, Polyhedron, 2015, 87, 311ꢀ320; (d) P. Chakraborty and S.
Mohanta, Polyhedron, 2015, 87, 98ꢀ108.
4
(a) S. Bhattacharya, A. Jana and S. Mohanta, CrystEngComm, 2013, 15, 10374ꢀ10382; (b) A.
Biswas, L. Mandal, S. Mondal, C. R. Lucas and S. Mohanta, CrystEngComm, 2013, 15, 5888ꢀ
897; (c) P. Bhowmik, H. P. Nayek, M. Corbella, N. AliagaꢀAlcalde and S. Chattopadhyay,
5
Dalton Trans., 2011, 40, 7916ꢀ7926; (d) P. Bhowmik, S. Jana, P. P. Jana, K. Harms and S.
Chattopadhyay, Inorg. Chim. Acta, 2012, 390, 53ꢀ60; (e) P. Bhowmik, S. Jana, P. P. Jana, K.
Harms and S. Chattopadhyay, Inorg. Chem. Commun., 2012, 18, 50ꢀ56; (f) P. Bhowmik, S. Jana,
S. Chattopadhyay, Polyhedron, 2012, 44, 11ꢀ17; (g) P. Bhowmik, K. Harms and S.
Chattopadhyay, Polyhedron, 2013 ,49, 113ꢀ120; (h) P. Bhowmik, N. AliagaꢀAlcalde, V. Gómez,
M. Corbella and S. Chattopadhyay, Polyhedron, 2013, 49, 269ꢀ276; (i) P. Bhowmik, S.
Chatterjee, S. Chattopadhyay, Polyhedron, 2013, 63, 214ꢀ221.
5
(a) K. Bhattacharya, M. Maity, Sk Md T. Abtab, M. C. Majee and M. Chaudhury, Inorg.
Chem., 2013, 52, 9597ꢀ9605; (b) A. Jana, R. Koner, T. Weyhermueller, P. Lemoine, M. Ghosh
and S. Mohanta, Inorg. Chim. Acta, 2011, 375, 263ꢀ270.
27

Dalton Transactions
Page 28 of 37
View Article Online
DOI: 10.1039/C6DT02587K
6
(a) E. Evangelio, N. P. Rath and L. M. Mirica, Dalton Trans., 2012, 41, 8010ꢀ8021; (b) X.
Gong, Y.ꢀY. Ge, M. Fang, Z.ꢀG. Gu, S.ꢀR. Zheng, W.ꢀS. Li, S.ꢀJ. Hu, S.ꢀB. Lib and Y.ꢀP. Cai,
CrystEngComm, 2011, 13, 6911ꢀ6915.
7
(a) S. Sasmal, S. Hazra, P. Kundu, S. Majumder, N. AliagaꢀAlcalde, E. Ruiz and S. Mohanta,
Inorg. Chem., 2010, 49, 9517ꢀ9526; (b) S. Hazra, R. Koner, P. Lemoine, E. C. Sañudo, and S.
Mohanta, Eur. J. Inorg. Chem., 2009, 3458ꢀ3466; (c) J. P. Wikstrom, A. Y. Nazarenko, W. M.
Reiff and E. V. RybakꢀAkimova, Inorg. Chim. Acta, 2007, 360, 3733ꢀ3740; (d) B. Biswas, U.
Pieper, T. Weyhermuller and P. Chaudhuri, Inorg. Chem. 2009, 48, 6781ꢀ6793; (e) J. M.
ClementeꢀJuan, B. Chansou, B. Donnadieu and J. Tuchagues, Inorg. Chem. 2000, 39, 5515ꢀ
5519; (f) S.ꢀY. Zhang, W.ꢀQ. Chen, B. Hu, Y.ꢀM. Chen, W. Li and Y. Li, Inorg. Chem.
Commun., 2012, 16, 74ꢀ77; (g) S.ꢀH. Zhang, N. Li, C.ꢀM. Ge, C. Fenga and L.ꢀF. Ma, Dalton
Trans., 2011, 40, 3000ꢀ3007.
8
2
(a) H. Y. Kwak, D. W. Ryu, H. C. Kim, E. K. Koh, B. K. Chod and C. S. Hong, Dalton Trans.,
009, 1954ꢀ1961; (b) H. Chen, C.ꢀB. Ma, D.ꢀQ. Yuan, M.ꢀQ. Hu, H.ꢀM. Wen, Q.ꢀT. Liu, and C.ꢀ
N. Chen, Inorg. Chem. 2011, 50, 10342ꢀ10352.
(a) S. Biswas, C. J. GómezꢀGarcía, J. M. ClementeꢀJuan, S. Benmansour and A. Ghosh, Inorg.
Chem. 2014, 53, 2441ꢀ2449; (b) L. K. Das and A. Ghosh, CrystEngComm, 2013, 15, 9444ꢀ9456;
c) S. L. Roderick and B. W. Matthews, Biochemistry 1993, 32, 3907ꢀ3912; (d) K. Ghosh, S.
Roy, A. Ghosh, A. Banerjee, A. Bauzá, A. Frontera, S. Chattopadhyay, Polyhedron, 2016, 112,
9
(
6
1
1
ꢀ17.
0 (a) J. Chen, J. Tang, J. Zhou, L. Zhang, G. Chen and D. Tang, Anal. Chim. Acta, 2014, 810,
0ꢀ16; (b) K. Mahata and M. Schmittel, J. Am. Chem. Soc., 2009, 131, 16544ꢀ16554.
28

Page 29 of 37
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT02587K
11 (a) Y.ꢀS. Yang, Y.ꢀP. Yang, M. Liu, Q.ꢀM. Qiu, Q.ꢀH. Jin, J.ꢀJ. Sun, H. Chen, Y.ꢀC. Dai and
Q.ꢀX. Meng, Polyhedron, 2015, 85, 912ꢀ917; (b) Y. Shen, N. Ma, L. Wu and H.ꢀH. Song, Inorg.
Chim. Acta, 2015, 429, 51ꢀ60; (c) A. Bhattacharyya, P. K. Bhaumik, P. P. Jana and S.
Chattopadhyay, Polyhedron, 2014, 78, 40ꢀ45; (c) S. Carboni, C. Gennari, L. Pignataro and U.
Piarulli, Dalton Trans., 2011, 40, 4355ꢀ4373.
12 (a) C. A. Hunter and J. K. M. Sanders, J. Am. Chem. Soc., 1990, 112, 5525ꢀ5534; (b) S. K.
Burley and G. A. Petsko, Science, 1985, 229, 23ꢀ28; (c) K. S. Kim, P. Tarakeshwar and J. Y.
Lee, Chem. Rev., 2000, 100, 4145ꢀ4185; (d) J. C. Ma and D. A. Dougherty, Chem. Rev., 1997,
97, 1303ꢀ1324; (e) K. S. Kim, J. Y. Lee, S. J. Lee, T.ꢀK. Ha and D. H. Kim, J. Am. Chem. Soc.,
1994, 116, 7399ꢀ7400; (f) M. Nishio, M. Hirota and Y. Umezawa, in The C–H/p Interaction:
Evidence, Nature, Consequences, WileyꢀVCH, New York, 1998; (g) M. Nishio, CrystEngComm,
004, 6, 130ꢀ156; (h) M. Egli and S. Sarkhel, Acc. Chem. Res., 2007, 40, 197ꢀ205; (i) T. J.
2
Mooibroek, P. Gamez and J. Reedijk, CrystEngComm, 2008, 10, 1501ꢀ1515; (j) J. Ran and P.
Hobza, J. Chem. Theory Comput., 2009, 5, 1180ꢀ1185; (k) M. Barcel´oꢀOliver, C. Estarellas, A.
GarcíaꢀRaso, A. Terrón, A. Frontera, D. Quiñonero, E. Molins and P. M. Deyà, CrystEngComm,
2
010, 12, 362ꢀ365; (l) D. Quiñonero, C. Garau, C. Rotger, A. Frontera, P. Ballester, A. Costa and
P. M. Dey`a, Angew. Chem., Int. Ed., 2002, 41, 3389ꢀ3392.
3 (a) D. Paolantoni, J. RubioꢀMagnieto, S. Cantel, J. Martinez, P. Dumy, M. Surin and S.
1
Ulrich, Chem. Commun., 2014, 50, 14257; (b) S. Jana, K. Harms and S. Chattopadhyay, J.
Coord. Chem., 2014, 67, 2954ꢀ2966; (c) C. Estarellas, A. Frontera, D. Quiæonero and P. M.
Deyà, Angew. Chem., Int. Ed., 2011, 50, 415.
14 (a) S. Naskar, D. Mishra, R. J. Butcher and S. K. Chattopadhyay, Polyhedron, 2007, 26,
3703ꢀ3714; (b) L. M. Salonen, M. Ellermann and F. Diederich, Angew. Chem., Int. Ed., 2011,
29