Synthesis, characterization, photoluminescent properties and supramolecular aggregations in diimine chelated cadmium dihalides

Article abstract of DOI:10.1080/00958972.2013.864393

A series of 12 new cadmium compounds, [Cd(X₂)(L)] (4, 10), [Cd(X₂)(L)(DMSO)] (9), [Cd(X₂)(L)]₂ (1-3, 5, 7, 8, 11, and 12), and [Cd(Cl₂)₂(L)]_n (6) where X = chloride, bromide, and

Full text of DOI:10.1080/00958972.2013.864393

This article was downloaded by: [Uppsala universitetsbibliotek]
On: 10 October 2014, At: 01:11
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis, characterization,
photoluminescent properties and
supramolecular aggregations in diimine
chelated cadmium dihalides
Tushar S. Basu Baula, Sajal Kundua, Seik Weng Ngbc, Nikhil
Guchhaitd & Edward R.T. Tiekinkb
a Department of Chemistry, North-Eastern Hill University, Shillong,
India
b Department of Chemistry, University of Malaya, Kuala Lumpur,
Malaysia
c Department of Chemistry, King Abdulaziz University, Jeddah,
Click for updates
Saudi Arabia
d Department of Chemistry, University of Calcutta, Kolkata, India
Accepted author version posted online: 13 Nov 2013.Published
online: 23 Dec 2013.
To cite this article: Tushar S. Basu Baul, Sajal Kundu, Seik Weng Ng, Nikhil Guchhait & Edward
R.T. Tiekink (2014) Synthesis, characterization, photoluminescent properties and supramolecular
aggregations in diimine chelated cadmium dihalides, Journal of Coordination Chemistry, 67:1,
96-119, DOI: 10.1080/00958972.2013.864393
To link to this article: http://dx.doi.org/10.1080/00958972.2013.864393
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Coordination Chemistry, 2014
Vol. 67, No. 1, 96–119, http://dx.doi.org/10.1080/00958972.2013.864393
Synthesis, characterization, photoluminescent properties and
supramolecular aggregations in diimine chelated cadmium
dihalides
TUSHAR S. BASU BAUL*†, SAJAL KUNDU†, SEIK WENG NG‡§,
NIKHIL GUCHHAIT¶ and EDWARD R.T. TIEKINK*‡
†Department of Chemistry, North-Eastern Hill University, Shillong, India
‡Department of Chemistry, University of Malaya, Kuala Lumpur, Malaysia
§Department of Chemistry, King Abdulaziz University, Jeddah, Saudi Arabia
¶Department of Chemistry, University of Calcutta, Kolkata, India
(Received 29 August 2013; accepted 31 October 2013)
Cadmium dihalide compounds of (E)-N-(pyridin-2-ylmethylidene) arylamines
can be tailored to be monomeric, dimeric and polymeric.
A series of 12 new cadmium compounds, [Cd(X2)(L)] (4, 10), [Cd(X2)(L)(DMSO)] (9), [Cd(X2)(L)]2
(1–3, 5, 7, 8, 11, and 12), and [Cd(Cl2)2(L)]n (6) where X = chloride, bromide, and iodide, and dii-
mine L = (E)-N-(pyridin-2-ylmethylidene)arylamine, were synthesized and characterized by elemental
1
analyses. The spectroscopic properties were investigated by IR, UV–Vis, fluorescence, and H NMR
studies. The solid-state structures of the 12 reaction products were studied by X-ray crystallography.
A majority of the structures are binuclear with five-coordinate cadmium centers: dimerization occurs
through μ2-bridging of the respective halides; the second halide is bound terminally. In the case of
X = Br and I, dimerization is circumvented when L carries an additional donor capable of coordinat-
ing cadmium (4, 10) or when the additional donor is provided by coordinating solvent (9). A similar
situation pertains in the CdCl2 analog (7). In the case where L strongly coordinates with cadmium,
i.e. (6), an edge-shared polymeric chain and octahedrally coordinated cadmium are found as a result
of μ2-bridging of both chloro ligands. An interesting feature of the crystal packing is the observation
of rare C–H…π interactions where the π-system is a chelate ring or a Cd2Br2 unit.
Keywords: Cadmium; (E)-N-(pyridin-2-ylmethylidene)arylamine; N,N-Donor ligands; Spectroscopy;
Structure elucidation; Supramolecular aggregations
*Corresponding authors. Emails: basubaul@nehu.ac.in, basubaulchem@gmail.com (T.S. Basu Baul);
Edward.Tiekink@gmail.com, Edward.Tiekink@um.edu.my (E.R.T. Tiekink)
© 2013 Taylor & Francis

Diimine cadmium dihalides
97
1. Introduction
Iminopyridyl-based ligands and metal complexes have found increasing application as
catalyst precursors in olefin polymerization following the discovery by Brookhart, Bennett,
and Gibson that five-coordinate 2,6-bis(arylimino)pyridyl metal dihalides (particularly Fe
and Co complexes), upon activation with methylaluminoxane, are efficient catalysts [1].
First and second row late-transition metal halide (Fe, Co, Ni, Cu, Pd) complexes of
bidentate (N,N′) (imino)pyridines show promising catalytic results; cobalt(II) complexes
were better performers in terms of activity for the oligomerization of ethylene to short-chain
α-olefins (C4–C12) [2–6]. Recently, the correlation of the structure of these (imino)pyridyl
(N,N′) metal complexes with their use as catalyst precursors for the homopolymerization,
oligomerization, and copolymerization of olefins has been described [7].
Construction of coordination networks by self-assembly has attracted considerable
attention in supramolecular chemistry and crystal engineering, owing to their potential
applications in gas storage [8, 9], photoluminescence [10, 11], catalysis [12–15], magnetism
[16], and molecular sensing [17, 18]. Supramolecular structures are affected by the structure
of ligands [19–22], the coordination geometry of metal ions [23], counter-anions [24–27],
hydrogen bonds [28–31], π–π stacking [32], etc.; among these, anions play a very important
role in the self-assembled construction. Metal complexes of chelating pyridine and diimines
continues to draw general interest in coordination chemistry and consequently they were
also investigated along with cadmium halides to afford complexes of compositions
[Cd(μ-X)2(L)2], [Cd(μ-X)2(L)2]11 (X = Cl, Br, I; L = monodentate N-donor ligands, e.g.
pyridine and derivatives) and [Cd(μ-X)2(4,4′-bipyridine)]21 (X = Cl, Br, I). Mononuclear
tetrahedral compounds are obtained when the most sterically demanding ligands are present,
e.g. I and 3,5-dimethylpyridine, while in all other cases 1- or 2-D coordination polymers
are observed [33]. In the polymeric chains, cadmium(II) cations are linked in an edge-
sharing fashion by halide bridges in their pseudo-equatorial plane, with terminal pyridine
ligands completing the pseudo-octahedral coordination sphere [33, 34]. The effects of anion
upon cadmium compounds containing chelating 2,2′-bipyridine (bipy) ligands have been
studied recently and in each instance a different structural type has been encountered,
e.g. [Cd(μ-Cl)2(bipy)]∞, [Cd(Br/I)2(bipy)2], [Cd(NO3)2(bipy)2], [Cd(NO3)(bipy)2(H2O)]
(NO3), [Cd(bipy)3](ClO4)2, and [Cd(O2CPh)2bipy(H2O)]·(H2O) where the coordination
geometry of cadmium atom is a distorted octahedral [35]. Among these, [Cd(O2CPh)2(bipy)
(H2O)]·(H2O) was found to efficiently catalyze the transesterification of a variety of esters
with methanol [36]. Underscoring the importance of reaction conditions, when the
aforementioned [Cd(I)2(bipy)2] compound was prepared by a hydrothermal route [36], the
same distorted octahedral geometry was revealed but now within a monoclinic (C2/c)
polymorph as opposed to the original orthorhombic (Pbcn) form [35]. The coordinating
properties of ambidentate ligand 5,5′-diamino-2,2′-bipyridine (5,5′-diamino-2,2′-bipy)
towards cadmium were investigated with the desire to generate tetrahedral or octahedral
building blocks for supramolecular assemblies based on chelation. The cadmium compound
[Cd(μ-Cl)2(5,5′-diamino-2,2′-bipy]11 forms 1-D polymeric strands constructed by bridging
chloro ligands and contains distorted octahedral cadmium centers comprising two nitrogens
of 5,5′-diamino-2,2′-bipy and four bridging chlorides [37]. A similar coordination geometry
around cadmium was observed in the structure of 1,10-phenanthroline (phen) compound
[Cd(μ-Cl)2phen]∞ which expands into a chain through the μ2-bridging of the chloro ligands
[38]. Owing to the presence of the large lateral aromatic phen ligand, the chains associate
via a strong π. . .π stacking interactions, resulting in a zipper-like, double-stranded chain

98
T.S. Basu Baul et al.
Chart 1. Chemical structures of molecules L1–L6 and formulation of cadmium(II) compounds 1–12.
[39]. The structures of bis(phen) compounds, e.g. [Cd(X)2(phen)2] where X = Cl [40] and
Br [41], are also known and the crystal packing of [Cd(Br)2(phen)2] is stabilized by
intermolecular π…π and C–H…Br interactions [41]. Ionic compounds of cadmium and
bipy were also prepared and shown to have diverse compositions, e.g. [Cd(bipy)3]
[PF6]2 [42], [Cd(bipy)2(H2O)(ClO4)][ClO4], [Cd(bipy)3][ClO4]2·0.5bipy [43], [Cd(bipy)3]
[ClO4]2·0.5H2O [44], a hydrothermal product [Cd(phen)2(H2O)2]SO4·6H2O [45], and a
bipy derivative [Cd(3,3′-diamino-bipy)3][NO3]2 [46]; each has a distorted octahedral
geometry around the cadmium atom.
We are recently engaged in a program to investigate the coordination behavior of
(E)-N-(pyridin-2-ylmethylidene)arylamines (L), which differ in the nature and location of
substituents in the aryl ring towards the zinc-triad elements with different anions. With
mercury(II), four types of neutral compounds were generated of formulae: [Hg(X)2L],
1
1
[Hg(μ-X)2L], [Hg(μ-NO3)(NO3)L]n , and {[Hg(μ-N3)2L]2}n [47]. In view of the observed
structural diversity in the mercury(II) structures, attention was directed towards cadmium
(II). Herein, five dibromo compounds with compositions [Cd(Br)2(Ln)]2 (1–3, 5) and
[Cd(Br)2(Ln)] (4), two dichloro compounds [Cd(Cl)2(Ln)]n (6) and [Cd(Cl)2(Ln)]2 (7), and
five diiodo compounds [Cd(I)2(Ln)]2 (8, 11, 12), [Cd(I)2(Ln)(DMSO)] (9) and [Cd(I)2(Ln)]
(10) are described (refer to chart 1 for chemical structures of Ln). Compounds 1–12 have
1
been characterized by IR and H NMR spectroscopic studies, and the solution and solid-
state photophysical properties are also discussed. Detailed structural information has been
afforded by single-crystal X-ray crystallographic analyses.
2. Experimental
2.1. Materials and physical measurements
All chemicals were used as purchased without purification: CdCl2 (Sarabhai chemicals),
CdBr2 (Sigma Aldrich), CdI2 (Sisco Research laboratories), aniline (Sd Fine), o-toluidine
(Thomas Bakers), p-toluidine (CDH), o-anisidine and p-anisidine (CDH), p-chloroaniline
(HiMedia), and pyridine-2-carboxaldehyde (Merck). Solvents were purified by standard pro-
cedures and freshly distilled prior to use. The (E)-N-(pyridin-2-ylmethylidene)arylamines
derivatives, L1–L6, were prepared in situ from pyridine-2-carboxaldehyde and the

Diimine cadmium dihalides
99
corresponding aniline [47]. Elemental analyses, solution electrical conductivity measure-
1
ments, IR, H NMR, and UV–vis spectra were recorded on instruments and under condi-
tions as described elsewhere [47]. Fluorescence spectra were obtained on a Hitachi model
FL4500 spectrofluorimeter (with the excitation and emission slits fixed at 10 and 20 nm,
respectively) and all spectra were corrected for the instrument response function and condi-
tions as described earlier [47]. Solid-state fluorescence spectra were obtained using a
Perkin–Elmer LS-55 spectrofluorimeter (with the excitation and emission slits fixed at 5
and 7.5 nm, respectively), and all spectra were corrected for the instrument response
function. A standard solid sample holder was used for mounting of solid sample and an
appropriate attenuator was used to avoid saturation of signal.
2.2. Synthesis of dihalocadmium(II) compounds (1–12)
[Cd(X2)(L)] (4, 10), [Cd(X2)(L)(DMSO)] (9), [Cd(X2)(L)]2 (1–3, 5, 7, 8, 11, and 12), and
[Cd(Cl2)2(L)]n (6)
The methods employed for the preparation of the dihalocadmium(II) compounds (1–12)
are very similar, so that the preparation of the dibromide derivative (1) is given in detail as
a representative example.
2.2.1. Synthesis of [Cd(Br)2(L1)]2 (1). To a solution of pyridine-2-carboxaldehyde
(0.172 g, 1.60 mM) in ethanol (5 mL) was added a solution of aniline (0.15 g, 1.61 mM) in
ethanol (5 mL). The mixture was stirred at ambient temperature for 30 min. To this reaction
mixture, CdBr2 (0.44 g, 1.61 mM) in methanol (20 mL) was added dropwise under stirring
which resulted in the immediate formation of a yellow precipitate. Stirring was continued for
3 h after which the mixture was filtered. The residue was washed with methanol (3 × 5 mL)
and dried in vacuo. The dried solid was dissolved by boiling in acetonitrile (60 mL) and fil-
tered while hot. The filtrate, upon cooling to room temperature, afforded a yellow crystalline
material. Yield 0.30 g (39%). M.p.: 258–260 °C. Found: C, 31.68; H, 2.32; N, 6.06%. Calcd
for C24H20Br4Cd2N4: C, 31.72; H, 2.22; N, 6.16%. Λm (CH3CN): 3.3 Ω−1cm2 M−1. IR
1
(cm−1): 1627 νasym(C(H)=N); 1591, 1492, 1436 ν(C=N)py. H-NMR (DMSO-d6): δ 9.15
[d, J = 4 Hz, 1H, H-3′], 8.66 [s, 1H, H-7], 8.14 [t, J = 8.0 Hz, 1H, H-5′], 7.93 [d, J = 8.0 Hz,
1H, H-6′], 7.77 [t, J = 6.4 Hz, 1H, H-4′], 7.43 [d, J = 8.0 Hz, 2H, H-3,5], 7.30 [m, 3H,
H-2,4,6] ppm. The atom numbering scheme employed is shown in chart 1.
2.2.2. Synthesis of [Cd(Br)2(L2)]2·C6H6 (2). A similar synthetic procedure as that used
for 1 was used except that aniline was replaced by o-toluidine, giving pale-yellow crystals
of the benzene monosolvate from acetonitrile/benzene (v/v, 6 : 1) solution. Yield 61%. M.p.:
172–175 °C. Found: C, 37.75; H, 3.10; N, 5.27%. Calcd for C32H30Br4Cd2N4: C, 37.86; H,
2.97; N, 5.52%. Λm (CH3CN): 3.5 Ω−1cm2 M−1. IR (cm−1): 1639 νasym(C(H)=N); 1600,
1
1500, 1447 ν(C=N)py. H-NMR (DMSO-d6): δ 8.97 [d, J = 4.0 Hz, 1H, H-3′], 8.57 [s, 1H,
H-7], 8.16 [t, J = 8.0 Hz, 1H, H-6′], 8.01 [d, J = 8.0 Hz, 1H, H-5′], 7.75 [t, J = 6.4 Hz, 1H,
H-4′], 7.21 [m, 3H, H-3,5,6], 7.01 [t, J = 6.4 Hz, 1H, H-4], 2.32 [s, 3H, CH3] ppm.
2.2.3. Synthesis of [Cd(Br)2(L3)]2 (3). A similar synthetic procedure as that used for 1
was used except that aniline was replaced by p-toluidine, giving pale-yellow crystals from

100
T.S. Basu Baul et al.
acetonitrile solution. Yield 55%. M.p.: 279–280 °C. Found: C, 33.02; H, 2.66; N, 6.19%.
Calcd for C26H24Br4Cd2N4: C, 33.37; H, 2.58; N, 5.98%. Λm (CH3CN): 2.0 Ω−1cm2 M−1.
IR (cm−1): 1626 νasym(C(H)=N); 1589, 1506, 1439 ν(C=N)py. 1H-NMR (DMSO-d6): δ
9.05 [d, J = 4.0 Hz, 1H, H-3′], 8.74 [s, 1H, H-7], 8.15 [t, J = 8.0 Hz, 1H, H-6′], 8.00
[d, J = 8.0 Hz, 1H, H-5′], 7.77 [t, J = 6.4 Hz, 1H, H-4′], 7.38 [d, J = 8.0 Hz, 2H, H-3,5],
7.16 [d, J = 8.0 Hz, 2H, H-2,6], 2.35 [s, 3H, CH3] ppm.
2.2.4. Synthesis of [Cd(Br)2(L4)] (4). A similar synthetic procedure as that used for 1 was
used except that aniline was replaced by o-anisidine, giving pale-yellow crystals from
acetonitrile/dimethylsulfoxide (v/v, 6 : 1) solution. Yield 49%. M.p.: 265–266 °C. Found: C,
32.44; H, 2.50; N, 5.66%. Calcd for C13H12Br2CdN2O: C, 32.26; H, 2.50; N, 5.79%. Λm
(CH3CN): 1.3 Ω−1cm2 M−1. IR (cm−1): 1623 νasym(C(H)=N); 1590, 1495, 1439 ν(C=N)py.
1H-NMR (DMSO-d6): δ 9.02 [s, 1H, H-7], 8.80 [d, 1H, H-3′], 8.13 [t, 1H, H-6′], 8.00
[d, 1H, H-5′], 7.73 [t, 1H, H-4′], 7.44 [d, 1H, H-6], 7.29 [t, 1H, H-4], 6.96 [m, 2H, H-3,5],
3.81 [s, 3H, OCH3] ppm.
2.2.5. Synthesis of [Cd(Br)2(L5)]2·2CH3CN (5). A similar synthetic procedure as that
used for 1 was used except that aniline was replaced by p-anisidine, giving-yellow
crystals of the acetonitrile disolvate from acetonitrile/dimethylsulfoxide (v/v, 6 : 1) solution.
Yield 55%. M.p.: 255–258 °C. Found: C, 34.05; H, 2.52; N, 7.50%. Calcd for
C30H30Br4Cd2N6O2: C, 34.28; H, 2.87; N, 7.99%. Λm (CH3CN): 1.5 Ω−1cm2 M−1. IR
1
(cm−1): 1624 νasym(C(H)=N); 1596, 1507, 1441 ν(C=N)py. H-NMR (DMSO-d6): δ 9.14
[d, J = 4.0 Hz, 1H, H-3′], 8.61 [s, 1H, H-7], 8.11 [t, J = 8.0 Hz, 1H, H-6′], 7.85 [d, J = 8.0 Hz,
1H, H-5′], 7.72 [t, J = 6.4 Hz, 1H, H-4′], 7.53 [d, br, 2H, H-3,5], 6.83 [d, J = 8.0 Hz, 2H,
H-2,6], 3.80 [s, 3H, OCH3] ppm.
2.2.6. Synthesis of [Cd(Cl)2(L2)] (6). A similar synthetic procedure as that used for 1 was
used except that CdBr2 and aniline were replaced by CdCl2 and o-toluidine, respectively,
giving pale-yellow crystals from acetonitrile. Yield 53%. M.p.: 242–245 °C. Found: C,
41.34; H, 3.22; N, 7.30%. Calcd for C13H12CdCl2N2: C, 41.14; H, 3.19; N, 7.38%. Λm
(CH3CN): 3.3 Ω−1cm2 M−1. IR (cm−1): 1639 νasym(C(H)=N); 1593, 1487, 1440 ν(C=N)py.
1H-NMR (DMSO-d6): δ 8.94 [d, J = 4.0 Hz, 1H, H-3′], 8.57 [s, 1H, H-7], 8.14 [t, J = 8.0 Hz,
1H, H-6′], 8.02 [d, J = 8.0 Hz, 1H, H-5′], 7.71 [t, 6.4 1H, H-4′], 7.19 [m, 3H, H-3,5,6],
6.99 [t, J = 6.4 Hz, 1H, H-4], 2.30 [s, 3H, CH3] ppm.
2.2.7. Synthesis of [Cd(Cl)2(L6)]2 (7). A similar synthetic procedure as that used for 1
was used except that CdBr2 and aniline were replaced by CdCl2 and p-chloroaniline,
respectively, giving pale-yellow crystals from acetonitile. Yield 41%. M.p.: 288–290 °C.
Found: C, 36.33; H, 2.20; N, 6.89%. Calcd for C24H18Cd2Cl6N4: C, 36.03; H, 2.26; N,
7.00%. Λm (CH3CN): 3.0 Ω−1cm2 M−1. IR (cm−1): 1624 νasym(C(H)=N); 1597, 1507, 1441
1
ν(C=N)py. H-NMR (DMSO-d6): δ 9.01 [d, J = 4.0 Hz, 1H, H-3′], 8.80 [s, 1H, H-7], 8.16
[t, J = 8.0 Hz, 1H, H-6′], 8.08 [d, J = 8.0 Hz, 1H, H-5′], 7.74 [t, J = 6.4 Hz, 1H, H-4′],
7.56 [d, J = 8.0 Hz, 2H, H-3,5], 7.40 [d, J = 8.0 Hz, 2H, H-2,6] ppm.

Diimine cadmium dihalides
101
2.2.8. Synthesis of [Cd(I)2(L3)]2 (8). A similar synthetic procedure as that used for 1 was
used except that CdBr2 and aniline were replaced by CdI2 and p-toluidine, respectively, giv-
ing pale-yellow crystals from acetonitile. Yield 35%. M.p.: 235–238 °C. Found: C, 27.48;
H, 2.44; N, 5.18%. Calcd for C26H24Cd2I4N4: C, 27.69; H, 2.14; N, 4.96%. Λm (CH3CN):
1
2.0 Ω−1cm2 M−1. IR (cm−1): 1635 νasym(C(H)=N); 1597, 1488, 1444 ν(C=N)py. H-NMR
(DMSO-d6): δ 8.91 [d, 1H, H-3′], 8.56 [s, 1H, H-7], 8.13 [t, 1H, H-6′], 7.94 [d, 1H, H-5′],
7.77 [t, 1H, H-4′], 7.00 [d, 2H, H-3,5], 6.88 [d, J = 8.0 Hz, 2H, H-2,6], 2.27 [s, 3H, CH3]
ppm.
2.2.9. Synthesis of [Cd(I)2(L3)(DMSO)] (9). A similar synthetic procedure as that used
for 1 was used except that CdBr2 and aniline were replaced by CdI2 and p-toluidine,
respectively, giving pale-yellow crystals from acetonitile/dimethylsulfoxide (v/v, 6 : 1) solu-
tion. Yield 35%. M.p.: 253–255 °C. Found: C, 28.18; H, 2.99; N, 4.26%. Calcd for
C15H18CdI2N2OS: C, 28.06; H, 2.82; N, 4.36%. Λm (CH3CN): 2.0 Ω−1cm2 M−1. IR
(cm−1): 1624 νasym(C(H)=N); 1596, 1507, 1441 ν(C=N)py; 1023 ν(S=O). 1H-NMR in
DMSO-d6 displayed signals identical to those observed for its uncoordinated DMSO
compound 8 and were indistinguishable.
2.2.10. Synthesis of [Cd(I)2(L4)] (10). A similar synthetic procedure as that used for 1 was
used except that CdBr2 and aniline were replaced by CdI2 and o-anisidine, respectively, giv-
ing pale-yellow crystals from acetonitile/dimethylsulfoxide (v/v, 6 : 1) solution. Yield 43%.
M.p.: 265–266 °C. Found: C, 27.19; H, 2.29; N, 5.04%. Calcd for C13H12CdI2N2O: C,
26.99; H, 2.09; N, 4.84%. Λm (CH3CN): 1.0 Ω−1cm2 M−1. IR (cm−1): 1618 νasym(C(H)
1
=N); 1589, 1495, 1438 ν(C=N)py. H-NMR (DMSO-d6): δ 9.08 [s, 1H, H-7], 8.88 [d,
J = 4.0 Hz, 1H, H-3′], 8.21 [t, J = 8.0 Hz, 1H, H-6′], 8.09 [d, J = 8.0 Hz, 1H, H-5′], 7.81
[t, J = 6.4 Hz, 1H, H-4′], 7.44 [d, J = 6.4 Hz, 1H, H-6], 7.36 [t, J = 8.0 Hz, 1H, H-4], 7.03
[m, 2H, H-3,5], 3.86 [s, 3H, OCH3] ppm.
2.2.11. Synthesis of [Cd(I)2(L5)]2 (11). A similar synthetic procedure as that used for 1
was used except that CdBr2 and aniline were replaced by CdI2 and p-anisidine, respectively,
giving pale-yellow crystals from acetonitile/dimethylsulfoxide (v/v, 6 : 1) solution. Yield
41%. M.p.: 202–205 °C. Found: C, 26.85; H, 2.22; N, 4.74%. Calcd for C26H24Cd2I4N4O2:
C, 26.99; H, 2.09; N, 4.84%. Λm (CH3CN): 2.0 Ω−1cm2 M−1. IR (cm−1): 1624 νasym(C(H)
1
=N); 1596, 1507, 1441 ν(C=N)py. H-NMR (DMSO-d6): δ 9.14 [d, J = 4.0 Hz, 1H, H-3′],
8.61 [s, 1H, H-7], 8.12 [t, J = 8.0 Hz, 1H, H-6′], 7.86 [d, J = 8.0 Hz, 1H, H-5′], 7.75 [t,
J = 6.4 Hz, 1H, H-4′], 7.49 [d, br, 2H, H-3,5], 6.84 [d, J = 8.0 Hz, 2H, H-2,6], 3.80 [s, 3H,
OCH3] ppm.
2.2.12. Synthesis of [Cd(I)2(L6)]2 (12). A similar synthetic procedure as that used for 1
was used except that CdBr2 and aniline were replaced by CdI2 and p-chloroaniline, respec-
tively, giving pale-yellow crystals from acetonitile solution. Yield 47%. M.p.: 238–240 °C.
Found: C, 24.80; H, 1.66; N, 4.80%. Calcd for C24H18Cd2Cl2I4N4: C, 24.68; H, 1.55; N,
4.79%. Λm (CH3CN): 2.0 Ω−1cm2 M−1. IR (cm−1): 1625 νasym(C(H)=N); 1591, 1489, 1440
1
ν(C=N)py. H-NMR (DMSO-d6): δ 9.12 [d, J = 4.0 Hz, 1H, H-3′], 8.66 [s, 1H, H-7], 8.12

102
T.S. Basu Baul et al.

Diimine cadmium dihalides
103

104
T.S. Basu Baul et al.
[t, J = 8.0 Hz, 1H, H-6′], 7.95 [d, J = 8.0 Hz, 1H, H-5′], 7.78 [t, J = 6.4 Hz, 1H, H-4′],
7.36 [d, J = 8.0 Hz, 2H, H-3,5], 7.26 [d, J = 8.0 Hz, 2H, H-2,6] ppm.
2.3. X-ray crystallography
Yellow/pale-yellow crystals of the compounds suitable for X-ray crystal structure
determination were obtained from acetonitrile/chloroform (v/v, 3 : 1) (1, 3, 6–8, and 12), or
acetonitrile/benzene/chloroform (v/v, 3 : 1 : 1) (2) or acetonitrile/dimethylsulfoxide (v/v, 6 : 1)
(4, 5, and 9–11) by slow evaporation of the solvent at room temperature. The intensity mea-
surements were made at 100 K on an Agilent Supernova dual diffractometer with an Atlas
(Mo) detector (ω scan technique) using graphite-monochromated Mo Kα radiation [48]. The
structures were solved by direct methods (SHELXS97 [49] through the WinGX Interface
[50]) and refined (anisotropic displacement parameters, H atoms in the riding model approx-
imation and a weighting scheme of the form w = 1/[σ2(Fo ) + aP2 + bP] where
2
P = (Fo + 2Fc )/3) with SHELXL97 on F2 [49]. The absolute structures of 4, 9, and 10
were determined on the basis of differences in Friedel pairs included in the respective
data-sets. When present, residual electron density peaks >1.0 eÅ−3 were located near the
Cd atom and/or near the halide (Br and I). The data collection and refinement parameters are
given in table 1, and views of the molecular structures are shown in figures 4–8, drawn at
the 50% probability level with ORTEP-3 for Windows [50]; the crystal packing
analysis was conducted with the aid of PLATON [51] and diagrams were drawn with
DIAMOND [52].
2
2
3. Results and discussion
3.1. Synthesis
To understand the structural trends of cadmium dihalide complexes with L, a series of 12
new compounds, 1–12 (chart 1), were synthesized. Synthesis was achieved by template
reactions between pyridine-2-carboxaldehyde, aniline, or derivatives and cadmium dihalides
in a mole ratio 1 : 1 : 1, according to a route described for cognate mercury(II) compounds
[47]. All cadmium compounds of the present investigation are insoluble in the reaction
medium, but can be recrystallized using a large volume of acetonitrile or combination of
acetonitrile and DMSO or only in DMSO. Molar conductivity measurements indicated that
1–12 are non-electrolytes. These results along with elemental analysis show that the M : X
ratio present in the original salts is preserved in the new compounds and that the L1–L6
ligands are present in neutral forms. Compounds 1–12 are all air-stable. The results of the
chemical and spectroscopic analyses are consistent with the crystal structure determinations
of 1–12 (see below).
3.2. Spectroscopic characterization
The infrared spectra of 1–12 are very similar, and the assignments of selected diagnostic
bands are given in the Experimental section. The compounds display a moderately intense
IR band at 1618–1640 cm−1, which is assigned to the νasym(C(H)=N) stretch of the coordi-
nated Schiff base ligands [47, 53]. In addition, well-resolved bands of variable intensity

Diimine cadmium dihalides
105
observed at 1600–1580, 1490–1475, and 1450–1435 cm−1 are assigned to the coordinated
pyridyl ring [53–55]. Compound 9, in addition to usual ν(C(H)=N) and ν(C=N)py bands,
displayed a very strong band at 1023 cm−1, which is attributed to ν(S=O) of the coordinated
DMSO molecule. This value is 35 cm−1 lower than that reported for free DMSO
(1055 cm−1) and is thus indicative of terminal (end-on) O-coordination. It should be noted
1
that for S-bonded DMSO, an increase in frequency is expected [56, 57]. The H NMR
spectra were recorded in DMSO-d6 solution which displayed the expected signals and inte-
gration values. In general, the signals were broad. However, coupling constants could be
determined in many cases, as detailed in the Experimental section; except for 4 and 8 owing
to complicated splitting yet the multiplicity patterns could be delineated. Compounds 2 and
1
5 should also display H NMR signals due to benzene and acetonitrile solvates but these
were obscured in the NMR spectra in DMSO-d6 solvent.
Table 2 summarizes the solution UV–vis and fluorescence properties of 1–12. The
absorption spectra of all compounds were recorded in the range 300–450 nm in acetonitrile
solutions at concentrations of ~10−5 M. The experimental absorption spectra comprise two
overlapping bands at 325–360 nm (figure S1 Supplemental data for this article can be
accessed http://dx.doi.org/10.1080/00958972.2013.864393); data for the free ligands are not
available for comparison as free ligands could not be isolated in pure forms. It is well
known that cadmium(II) compounds show excellent luminescence properties [58] and
accordingly, the photoluminescence properties of 1–12 in acetonitrile solution were investi-
gated. Generally, at room temperature, broad fluorescent emission bands at λmax = 405 nm
along with a shoulder in the range ~440–455 nm were observed. The exceptional spectra
were for each of 4 and 10, i.e. the o-methoxy derivatives, which appeared at higher wave-
lengths, i.e. ~495 nm, when they are excited at their respective absorption maxima (figure
S2). These emissions could not be assigned as metal-to-ligand charge transfer (MLCT) or
ligand-to-metal charge transfer (LMCT) as the cadmium(II) ion, with a d10 configuration, is
not easy to oxidize or reduce [59]. The emissions are therefore attributed to the intraligand
(IL) (π–pꢀ) fluorescent emission. Recently, a molecule containing a related ligand backbone
as in L1–L6, i.e. (E)-4-((pyridin-2-ylmethylidene)amino)phenol was synthesized and found
Table 2. Photophysical data for 1–12 recorded in acetonitrile solution and in the solid-state.
Photoluminescence data
Solution-state
em (nm)a
Solid-state
Compounds
Electronic spectroscopic data λmax (nm); (ε[M−1])
λ
ϕF
λem (nm)a
1
2
3
4
324 (12,272)
334 (9605)
403, 441
404, 446
404, 442
404, 497
0.06
0.04
0.07
0.04
425, 490
452, 485
434, 484
491
341 (13,320)
310 (12,500)
365 (14,717)
363 (14,637)
331 (7904)
334 (11,133)
334 (15,896)
334 (15,397)
315 (15,291)
367 (17,815)
365 (17,718)
326 (15,920)
5
6
7
8
9
10
404, 446
403, 443
404, 439
406, 439
403, 447
406, 496
0.03
0.05
0.03
0.05
0.02
0.11
498
414, 487
437, 482
443, 482
435, 487
482, 518
11
12
406, 454
403, 442
0.03
0.01
517
451, 480
aThe high energy wavelength emission appears as a shoulder in all cases.

106
T.S. Basu Baul et al.
to be non-emissive in solution and in the solid state, even at 77 K [60]. However, such
observations should not be generalized for the emission properties of L. Overall, the present
investigation show very low fluorescent quantum yields (table 2), indicating that the
cadmium(II) compounds are weak emitters at room temperature. The small variations in
photoluminescence across the series may be attributed to differences in the constitution of
L, anions and/or their local coordination environment. The solid-state fluorescence spectra
for all the assayed compounds at room temperature displayed rather a broad emission band
at λmax ~445 nm along with a shoulder in the range ~475–490 nm akin to that observed in
solution, except for those with –OMe substituent at Y or Z position (cf. Chart 1; compounds
4, 5, 10, and 11). Interestingly, 4, 5, 10, and 11 show a single band emission which is
appreciably red-shifted with respect to the other investigated compounds (cf. figure S3).
Similar behavior was noted in the spectra of acetonitrile solution and such shift could be
attributed to extra stabilization by the –OMe substitution. The presence of –OMe group at
the ortho-position in 4 and 10 hindered flexible motion at the connecting N-center through
crowding and thereby increase fluorescence by resisting non-radiative channels which is
usually active through flexible modes in solution phase. However, such possibility is absent
when –OMe group is at the para-position and hence the observed fluorescence intensities
of the red-shifted band of 5 and 11 are low in solution. On the other hand, in the solid
matrix such non-radiative channels through flexible modes are absent by rigid solid matrix
and hence the fluorescence intensity of the red-shifted band for all the compounds (4, 5, 10
and 11) is high. Such observation clearly suggests that in those compounds there is an
intraligand charge transfer which stabilizes the whole system and thus accounts for the
observed red shift [61, 62].
3.3. Molecular structures
The crystal and molecular structures of 1–12 have been determined; crystal data and
selected geometric parameters are shown in tables 1 and 3, respectively. The structures of
the CdBr2 series (1–5) are discussed first and then related to their CdCl2 (6, 7) and CdI2
(8–12) analogs. The structural motifs range from mononuclear to binuclear and polymeric
with variations related to the Lewis acidity of the cadmium center, coordination of
additional donor atoms on the Ln ligands, chelating ability of Ln, and due to interaction with
solvent molecules.
The molecular structure of [Cd(Br)2(L1)]2 (1) is shown in figure 1 and serves as the pro-
totype for the majority of structures described herein. The binuclear molecule is generated
by the application of a center of inversion and features two cadmium ions bridged in an
asymmetric manner by two bromo ligands. As anticipated, the Cd–Br (bridging) distances
are longer than the terminal Cd–Br bond length. L chelates through the nitrogen atoms,
consistent with an earlier analysis [47]; the Cd–N(pyridyl) bond length is significantly
shorter than the Cd–N(imino) bond length, a trend that holds true of all binuclear molecules
in the present study. The ligand backbone is planar as seen in the values of the N1–C5–C6–
N2 torsion angles and this planarity is sometimes extended to include the pendant aryl ring
(table 3). The resultant five-membered CdN2C2 chelate ring is planar with the root-mean-
square (r.m.s.) deviation of the fitted atoms being 0.049 Å. The Br3N2 donor set defines a
coordination geometry approaching square pyramidal as quantified by the value of τ = 0.27
which compares to the τ values of 0.0 and 1.0 for ideal square pyramidal and trigonal
bipyramidal geometries, respectively [63]. A partial explanation for the distortion is traced

Diimine cadmium dihalides
Table 3. Selected geometric parameters (Å, °) for 1–12.
107
Compound
1 (X = Br)
2 (X = Br)
3 (X = Br)
4 (X = Br)
5 (X = Br)
6 (X = Cl)a
Cd–X1
Cd–X1i
2.6869(7)
2.7689(7)
2.5388(7)
2.312(4)
2.405(4)
–
2.6330(3)
2.8076(3)
2.5571(3)
2.301(2)
2.412(2
2.6376(4)
2.5369(9)
2.6555(4)
2.8005(4)
2.5578(4)
2.287(2)
2.408(2)
–
2.5787(6)
2.6547(6)
2.5163(6)
2.351(2)
2.8021(4)
2.5486(4)
2.287(3)
2.413(2)
–
–
2.5397(9)
2.324(5)
2.321(6)
2.504(4) (O1)
71.71(18)
116.45(3)
–
Cd–X2
Cd–N1
Cd–N2
2.4260(19)
2.6917(6) (Cl2ii)
69.94(6)
Cd–Y
–
N1–Cd–N2
X1–Cd–X2
X1–Cd–X1i
X2–Cd–X1i
X1–Cd–N1
X1i–Cd–N2
N1–Cd–Y
Cd–X1–Cdi
N2–C6
71.92(15)
109.69(2)
86.40(2)
105.13(2)
131.83(11)
148.24(10)
–
72.03(7)
130.987(12)
85.124(10)
97.875(10)
128.92(5)
151.86(5)
–
72.37(9)
127.487(15)
87.016(12)
97.708(13)
116.33(7)
158.92(6)
–
72.36(8)
117.848(13)
86.337(11)
99.436(11)
118.27(6)
159.39(6)
–
103.15(2)
85.563(17)
96.930(19)
92.71(5)
–
102.78(15)
–
80.89(5)
135.52(18) (O1)
–
80.38(5) (Cl2ii)
94.437(17)
1.264(3)
93.60(2)
1.288(7)
4.9(8)
94.876(10)
1.286(3)
−6.9(3)
92.984(12)
1.280(4)
4.9(5)
93.663(11)
1.279(4)
2.0(4)
1.277(8)
−0.9(10)
13.1(11)
–
N1–C5–C6–N2
C6–N2–C7–C8
Symmetry operation:
9.6(3)
−16.9(8)
2 − x, 1 − y, 1 − z
−40.9(3)
1 − x, 1 − y, 1 − z
−13.0(5)
1 − x, 1 − y, 1 − z
−7.6(4)
−128.1(3)
1 − x, 1 − y, 1 − z
1 − x, 1 − y, 1 − z
Compound
7 (X = Cl)
8 (X = I)
9 (X = I)
10 (X = I)
11 (X = I)
12 (X = I)
Cd–X1
Cd–X1i
2.5122(15)
2.6505(15)
2.4119(16)
2.277(5)
2.388(5)
–
2.8611(5)
2.9865(6)
2.7295(6)
2.338(4)
2.428(4)
–
2.7636(5)
–
2.7182(7)
–
2.8009(3)
3.0513(4)
2.7416(3)
2.305(3)
2.438(3)
–
2.8340(3)
3.0021(3)
2.7206(3)
2.305(2)
2.431(2)
–
Cd–X2
2.7541(5)
2.303(4)
2.440(4)
2.366(4) (O1)
71.60(15)
120.089(16)
–
2.7090(7)
2.319(6)
2.313(6)
2.534(5) (O1)
71.4(2)
117.32(2)
–
Cd–N1
Cd–N2
Cd–Y
N1–Cd–N2
X1–Cd–X2
X1–Cd–X1i
X2–Cd–X1i
X1–Cd–N1
X1i–Cd–N2
N1–Cd–Y
Cd–X1–Cdi
N2–C6
72.10(17)
123.47(6)
88.27(5)
94.70(5)
111.21(13)
160.33(13)
–
71.00(15)
113.360(18)
87.519(16)
100.769(16)
121.49(11)
152.60(11)
–
71.33(10)
122.881(12)
88.887(10)
96.992(10)
111.89(7)
162.32(7)
–
71.68(8)
125.655(10)
86.383(8)
102.125(9)
117.96(6)
154.36(6)
–
–
–
114.51(11)
–
113.54(16)
–
82.25(14)
–
134.1(2)
–
91.73(5)
1.274(8)
4.3(9)
87.519(16)
1.269(7)
−3.0(8)
84.313(10)
1.278(4)
−0.8(5)
86.383(8)
1.277(4)
−1.3(4)
1.278(6)
−1.4(8)
3.7(8)
1.283(9)
1.1(10)
−13.1(11)
–
N1–C5–C6–N2
C6–N2–C7–C8
Symmetry operation i:
−21.9(9)
1 − x, 1 − y, 1 − z
11.8(8)
5.3(5)
3.4(4)
−x, 1 − y, 1 − z
–
1 − x, y, ½ − z
1 − x, 1 − y, 1 − z
aSymmetry operation ii: 2 − x, 1 − y, 1 − z; additional angles: Cl1i–Cd–Cl2ii
Cl2–Cd–N1 = 157.47(5), Cd–Cl2–Cdii = 97.058(19)°.
=
178.214(18), Cl1–Cd–N2 = 155.49(6),
to the restricted bite angle of L. Allowing for chemical differences, very similar binuclear
molecular structures are found for [Cd(Br)2(L2)]2·C6H6 (2) and [Cd(Br)2(L3)]2 (3), where
each of L2 and L3 carries a methyl substituent in the aryl ring (figure S4).
Each binuclear molecule of 2 and 3 is located about a center of inversion. A solvent
benzene molecule, also disposed about a center of inversion, crystallized with 2 so that the
overall stoichiometry is [Cd(Br)2(L2)]2·C6H6. The τ values of 0.35 and 0.52, respectively,
are closer to trigonal bipyramidal than observed in 1. The Cd–Br bridges are less symmetric
in these structures with Δ(Cd–Br) = difference in the Cd–Br(bridging) distances = 0.175
and 0.165 Å, respectively, compared with Δ(Cd–Br) = 0.082 Å in 1. The greater asymmetry
in each of 2 and 3 arises as a result of the contraction of the shorter Cd–Br bridging
distance and elongation of the longer Cd–Br(bridge) distance; there is also an elongation of
the terminal Cd–Br bond length. These observations are correlated with the better

108
T.S. Basu Baul et al.
Figure 1. Molecular structure of binuclear [Cd(Br)2(L1)]2 (1). Unlabeled atoms are related by the symmetry
operation 2 − x, 1 − y, 1 − z. Allowing for differences in halide and substituents in L, the molecular structures of
[Cd(Br)2(L2)]2·C6H6 (2), [Cd(Br)2(L3)]2 (3), [Cd(Br)2(L5)]2·2CH3CN (5), [Cd(Cl)2(L6)]2 (7), [Cd(I)2(L3)]2 (8) and
[Cd(I)2(L6)]2 (12) are the same and are illustrated in figure S1. The numbering scheme for the halides and L are as
shown for 1.
Figure 2. Molecular structure of mononuclear [Cd(Br)2(L4)] (4).
coordinating ability of L2 and L3 compared with L1, owing to the presence of methyl sub-
stituents in the former [47]. Systematic variations in the Cd–N bond lengths cannot be
delineated with confidence, owing to the relative high errors associated with these parame-
ters.
When the methyl substituent in L2 is replaced by a methoxy group to give L4, a major
structural change occurs, owing to the coordination of the methoxy-O1 atom to cadmium
(figure 2). In 4, the five-coordinate donor set is based on a Br2N2O environment that defines
a distorted square pyramidal geometry (τ = 0.10) with the apical position occupied by the
Br2 atom. The Cd–Br bond lengths differ by only 0.028 Å and are comparable with the ter-
minal Cd–Br bond length in 1; the Cd–N bond lengths are similarly equivalent. The second
chelate ring formed owing to the interaction of the methoxy atom is non-planar and best

Diimine cadmium dihalides
109
Figure 3. A segment of the polymeric structure in [Cd(Cl)2(L2)]n (6). Symmetry operations i: 1 − x, 1 − y, 1 − z
and ii: 2 − x, 1 − y, 1 − z.
described as an envelope with the Cd atom being the flap atom; the dihedral angle between
the five-membered rings is 12.8(3)°.
The structure of 5 crystallized about a center of inversion along with a solvent
acetonitrile molecule so that the overall composition is [Cd(Br)2(L5)]·2CH3CN (figure S4).
The binuclear structure of 5, with a methoxy group in the 4-position, resembles that of 3
but with a small elongation in Cd–Br1 which is compensated by a small reduction in the
Cd–Br1i bond length, Δ(Cd–N) = 0.146 Å; τ = 0.60. Only one structure containing CdCl2
was obtained that is directly comparable with the aforementioned CdBr2 structures, namely
[Cd(Cl)2(L2)]n (6) (figure 3). A segment of the polymeric structure of [Cd(Cl)2(L2)]n (6) is
shown in figure 3. The cadmium atom is chelated by L2 and surrounded by four μ2-chloro
ligands with the resulting Cl4N2 donor set defining a distorted octahedral geometry. Pairs of
bridging μ2-chloro ligands bridge differently with one almost being symmetric but the other
with a disparity in the Cd–Cl bond lengths, Δ(Cd–Cl) = 0.076 and 0.175 Å, respectively.
The presence of stronger Cd–Cl bonds compared with Cd–Br bond in 2 results in a general
elongation of the Cd–N bond lengths in 6 compared with those in 2. The formation of a
polymer in 6 and not in 2 can be correlated with the greater electronegativity of chloride
over bromide which enhances the Lewis acidity of the cadmium atom which compensates
by forming intermolecular interactions. The polymeric structure with a zigzag topology
comprises edge-shared polyhedra propagated along the a-axis. While it was not possible to
isolate crystals of a compound formed between CdBr2 and L6, crystals of the 1 : 1
compound with CdCl2 were characterized as [Cd(Cl)2(L6)]2 (7).
The molecular structure of binuclear [Cd(Cl)2(L6)]2 (7), figure S4, resembles closely
that of binuclear species described above. The Cd–Cl bridges are not symmetric with
Δ(Cd–Cl) = 0.138 Å and the value of τ = 60. The question arises as to why this species is
binuclear rather than polymeric as for 6 – a possible answer lies in the relative coordinating
abilities of L. In 6, the L2 ligand, with an electron-donating methyl group chelates the

110
T.S. Basu Baul et al.
Figure 4. Molecular structure of mononuclear [Cd(I)2(L3)(DMSO)] (9).
cadmium center relatively strongly, as established above for the CdBr2 structures. This, in
turn, reduces the strength of the Cd–Cl bonds. The chloro ligands in 6 compensate by
bridging. Attention is now directed to the five crystal structure determinations featuring
CdI2.
Allowing for elongation of the Cd–I bond lengths, the pattern of geometric parameters
describing the coordination geometry in [Cd(I)2(L3)]2 (8), figure S4, follows that established
for 3; Δ(Cd–I) = 0.125 Å; τ = 0.46. While 8 was isolated from an acetonitrile/chloroform
(v/v, 3 : 1) solution, when crystallization was from acetonitrile/dimethylsulfoxide (v/v, 6 : 1),
mononuclear [Cd(I)2(L3)(DMSO)] (9), figure 4, was isolated. The DMSO molecule
coordinates via the O atom and the ensuing I2 N2O donor set in 9 defines a geometry
almost intermediate between square pyramidal and trigonal bipyramidal with τ = 0.48.
Figure 5. Molecular structure of binuclear [Cd(I)2(L5)]2 (11). Unlabeled atoms are related by the symmetry
operation 1 − x, y, ½ − z.

Diimine cadmium dihalides
111
Unlike the five-coordinate structure [Cd(Br2)(L4)] (4), there is only a small difference in the
Cd–I bond lengths in 9, 0.01 Å; the Cd–N bond distances retain their expected disparity.
A five-coordinate geometry is also found in the structure of [Cd(I)2(L4)] (10), figure S4,
a direct analog of [Cd(Br)2(L4)] (4), owing to the coordination of the methoxy-O atom in
the 2-position of the aryl ring. The I2N2O donor set defines a geometry based on a square
pyramidal with τ = 0.03 with the I1 atom occupying the apical position. The CdOC2N
chleate has an envelope conformation with the Cd atom being the flap atom; the dihedral
angle between the five-membered rings is 13.5(3)°. As with 4, but in contrast with all other
structures reported herein, the Cd–N bond lengths in 10 are experimentally equivalent. The
difference occurs as the Cd–N(imino) bond lengths contract in 4 and 10, an observation
correlated with the fact that the N(imino) is no longer trans to a halide atom as in the
remaining structures.
The final two structures to be described are binuclear. The structure of [Cd(I)2(L5)]2 (11),
figure 5, stands out in that the molecule has crystallographic twofold symmetry rather than
being centrosymmetric as for the other binuclear structures. The key structural consequence
is that the terminal halide atoms are approximately syn as opposed to anti as found in the
centrosymmetric structures. As the ligand L5 is found in a structure with an anti conforma-
tion, i.e. 5, and the remaining binuclear CdI2 structures also adopt anti conformations, no
obvious explanation is apparent for the adoption of the syn conformation in 11. Other than
this conformational difference, there are no significant differences in geometric parameters
that are evident; Δ(Cd–I) = 0.250 Å and τ = 0.63. The structure of [Cd(I)2(L6)]2 (12),
figure S4, conforms to the generally observed centrosymmetric binuclear motif with
Δ(Cd–I) = 0.168 Å and τ = 0.48. The unexpected observation for 11, notwithstanding the
fact that 12 and that of the CdCl2 analog 7 both adopt the same structural motif, suggests
that the CdBr2 analog is likely to have the same structure.
A search of the Cambridge Structural Database [64] indicates that when complexed, mol-
ecules L1–L6 are invariably chelating. With the exception of the recent systematic study of
mercury analogs [47], there are only three other literature precedents of these molecules
with the zinc-triad elements. Each of the zinc compounds, i.e. [Zn(Cl)2(L1)] [65] and
[Zn(I)2(L1)] [66], is mononuclear and the sole mercury structure is binuclear, i.e.
[Hg(Cl)2(L1)] [67]. Even from this limited database, some conclusions may be proffered.
Thus, ZnX2 compounds with Ln are likely to be mononuclear while those of CdX2 and
HgX2 are generally more likely to increase the coordination number of the central atom via
halide bridges to form binuclear species. The trend to aggregate increases in the order
Cl > Br > I, a trend related to the electronegativity of the halide, as discussed above.
While there are no related crystal structures of the general formula [M(X)2(Ln)], where M
is any heavy element and X is a halide for n = 1–3, examples do exist when n = 4–6. Thus,
when n = 4, a five-coordinate copper(II) complex, [Cu(Cl)2(L4)] [68], resembles closely that
reported above for [Cd(Br)2(L4)] (4). Two examples exist for L5. Binuclear [Cu(I)2(L5)]2
[69] resembles [Cd(I)2(L5)]2 (11) but has an anti conformation of the L5 ligands, rather than
syn as in 11. The second literature structure with L5 is mononuclear and square planar
[Pt(Cl)2(L5)] [70]. Finally, mononuclear and square planar [Pt(Cl)2(L6)], isolated as an
acetonitrile solvate [71], contrast each of binuclear [Cd(Cl)2(L6)]2 (7) and [Cd(I)2(L6)]2 (12).
3.4. Supramolecular aggregation
The crystal packing of 1 is dominated by π…π interactions with the resulting supramolecu-
lar architecture being a 2-D array in the ab-plane (figure 6). The closest of these interactions

112
T.S. Basu Baul et al.
Figure 6. A view of the supramolecular layer in the ab-plane in 1. The π. . .π interactions are indicated as purple
dashed lines. For the (Cd, N1, N2, C5, C6) and (N1, C1–C5)i rings, the inter-centroid distance = 3.756(3) Å, the
angle of inclination between the rings = 4.8(3)° for symmetry operation i: 1 − x, −y, 1 − z. For the (N1, C1–C5)
and (C7–C12)ii rings, inter-centroid distance = 3.904(4) Å, angle of inclination = 12.1(3)° for symmetry operation
ii: 2 − x, −y, 1 − z (see http://dx.doi.org/10.1080/00958972.2013.864393 for color version).
[3.756(3) Å] occurs between the chelate ring and the pyridyl ring; geometric details are
given in the caption to figure 9. Increasingly, such interactions involving chelate rings,
having metallaromatic character [72], are appreciated as being important in stabilizing the
crystal structures containing metal chelates [73, 74]. Complementing these interactions are
contacts between the pyridyl and phenyl rings. In the crystal structure, the aryl rings pro-
jecting to either side of the layers partially inter-digitate along the c-axis, see ESI figure S5.
Compound 8 is isostructural with 1 and details are included in ESI figure S6.
The structure of binuclear 2 was characterized as its benzene monosolvate. Molecules
aggregate into a supramolecular chain along the a-axis via C–H…Br and C–H…π

Diimine cadmium dihalides
113
Figure 7. Crystal packing for 2. (a) Supramolecular chain along the a-axis sustained by C–H. . .Br
[C6–H6. . .Br2i = 2.80 Å, C6. . .Br2i = 3.699(2) Å and angle at H6 = 157° for symmetry operation i: −1 + x, y, z]
and C–H. . .π [C8–H8. . .Cg(Cd2Br2)i = 2.89 Å, C8. . .Cg(Cd2Br2)i = 3.768(3) Å with angle at H8 = 154°]
interactions shown as brown and brown dashed lines, respectively. (b) View of the unit cell contents in projection
down the a-axis, the direction of the supramolecular chains, highlighting the formation of columns in which resides
the solvent benzene shown in a space-filling mode. The π. . .π interactions [(N1,C1–C5) and (N1,C1–C5)ii rings,
inter-centroid distance = 3.8755(16) Å, angle of inclination = 0° for symmetry operation ii: −x, 1 − y, 1 − z] are
shown as purple dashed lines (see http://dx.doi.org/10.1080/00958972.2013.864393 for color version).

114
T.S. Basu Baul et al.
interactions (figure 7(a)). In this case, the π-system is the Cd2Br2 ring which, having metal-
loaromatic character, is capable of forming such interactions [74, 75]. Chains are linked into
layers in the ab-plane by π…π interactions between the pyridyl rings. While there are no
specific interactions between the layers and benzene molecules, the columns in the crystal
defined by the partially inter-digitating layers accommodate the benzene molecules
(figure 7(b)).
The 3-D architecture in 3 is constructed by a combination of C–H. . .Br interactions
involving the H3 and H6 atoms of L3 connected to two different Br atoms, as well as two
distinct π. . .π interactions occurring between the pyridyl and tolyl rings. The unit cell
contents are illustrated in figure S7. While 3 has a methyl group in the 4-position of the aryl
ring, substitution by chloride does not change the crystal packing in isostructural 7
(figure S8). Compound 12 is also isostructural but in this case, further stabilization to the
crystal structure is provided by an additional C–H. . .Cl interaction involving a hydrogen
atom already interacting with an iodide so that this atom (H3) is bifurcated as detailed in
figure S9.
Thus, in isostructural 3, 7, and 12 different points of contact are identified based on
the geometric parameters encompassed in PLATON [51]. The isostructural behavior,
despite the presence of varying supramolecular synthons, points to the importance of
global crystal packing of the molecules, i.e. close packing of irregularly shaped
Figure 8. The supramolecular array in the ac-plane for 4 sustained by C–H. . .Br [C6–H6. . .Br1i = 2.90 Å,
C6. . .Br1i = 3.800(7) Å and angle at H6 = 158° for symmetry operation i: −1 + x, y, −1 + z] and π. . .π [(C7–C12)
and (C7–C12)ii rings the inter-centroid distance = 4.065(4) Å, the angle of inclination between the rings = 12.8(3)°
for symmetry operation ii: x, −y, −½ − z] interactions, indicated as orange and purple dashed lines, respectively
(see http://dx.doi.org/10.1080/00958972.2013.864393 for color version).

Diimine cadmium dihalides
115
Figure 9. Unit cell contents for 5 viewed in projection down the a-axis. The C–H. . .Br [C11–H11. . .Br2i = 2.93
Å, C6. . .Br2i = 3.737(3) Å and angle at H6 = 144° for symmetry operation i: 1 − x, 1 − y, −z; C15–
H15a. . .Br2ii = 2.84 Å, C11. . .Br2ii = 3.789(3) Å and 144° for ii: 2 − x, −y, 1 − z], C–H. . .N [C2–H2. . .N3 = 2.47
Å, C2. . .N3 = 3.412(4) Å and 172°; C13–H13b. . .N3iii = 2.58 Å, C13. . .N4iii = 3.456(5) Å and H13b = 149° for
iii: x, 1 + y, −1 + z], C–H. . .π [C15–H15b. . .Cg(C7–C12)iv = 2.63 Å, C15. . .Cg(C7–C12)iv = 3.460(3) Å and angle
at H15b = 142° for iv: 2 − x, 1 − y, 1 − z], and π. . .π [(Cd,N1,N2,C5,C6) and (C7–C12)v rings the inter-centroid
distance = 3.8996(16) Å, the angle of inclination between the rings = 8.21(12)° for v: 2 − x, 1 − y, −z; (N1,C1–
C5). . .(N1,C1–C5)iv = 3.6079(16) Å, angle = 0°; (N1,C1–C5). . .(C7–C12)v = 3.5781(16) Å, angle = 5.49(13)°]
interactions are shown as orange, blue, brown and purple dashed lines, respectively (see http://dx.doi.org/10.1080/
00958972.2013.864393 for color version).
molecules [74, 76]. This conclusion is also borne out in the crystal packing of 4 and 10.
The structures of mononuclear 4 and 10, featuring coordinated methoxy atoms, are
isostructural. The key feature of the crystal packing is the formation of a supramolecular
layer in the ac-plane through a combination of C–H. . .Br and weak π. . .π interactions,
the latter occurring between phenyl rings, as detailed in figure 8; a view of the unit cell
contents for 4 is shown in figure S10 and full details for 10 are given in figure S11. In
10, the π. . .π interactions are weaker but an additional C–H. . .I interaction occurs, which
provide some cohesion between layers.
The structure of binuclear 5 was characterized as its acetonitrile disolvate. A 3-D
architecture sustained by C–H. . .Br and π. . .π interactions is formed and this defines chan-
nels running parallel to the a-axis. Inside these reside the acetonitrile molecules which are
held in place by C–H. . .Br, C–H. . .π and C–H. . .N interactions (figure 9). It is noteworthy
that one of the π. . .π contacts involves the chelate ring interacting with a phenyl ring.
The remaining three crystal structures are stand-alone in that they are not isostructural with
other molecules reported herein. Nevertheless, a common feature of their crystal packing is
the formation of 2-D arrays. The polymeric chains in 6 are connected to translationally

116
T.S. Basu Baul et al.
Figure 10. A view of the supramolecular array in the bc-plane for 9 sustained by C–H. . .π [C13–H13c. . .Cg(Cd,
N1,N2,C5,C6)i = 2.99 Å, C13. . .Cg(Cd,N1,N2,C5,C6)i = 3.768(6) Å and angle at H13c = 138° for symmetry oper-
ation i: x, y, −1 + z; C14–H14c. . .Cg(N1,C1–C5)ii = 2.92 Å, C13. . .Cg(Cd,N1,N2,C5,C6)ii = 3.738(6) Å and angle
at H14c = 142° for symmetry operation ii: −x, −½ + y, 1 − z] and π. . .π [(N1,C1–C5) and (C7–C12)iii rings the
inter-centroid distance = 3.594(3) Å, the angle of inclination between the rings = 4.7(3)° for symmetry operation
iii: x, y, 1 + z] interactions, indicated as brown and purple dashed lines, respectively (see http://dx.doi.org/10.1080/
00958972.2013.864393 for color version).
related chains along the b-axis by C–H. . .Cl and π. . .π [between tolyl rings] interactions to
form a supramolecular layer in the ab-plane (figure S12(a)). Layers stack along the c-axis
with no specific interactions between them (ESI figure S12(b)). The supramolecular array in
the crystal structure of mononuclear 9 is sustained by C–H. . .π interactions whereby one
DMSO-methyl group forms a contact with a pyridyl ring, and the tolyl-methyl forms a con-
tact with the π-system defined by the chelate ring. Layers in the bc-plane are consolidated by
π. . .π interactions between the pyridyl and tolyl rings (figure 10); the layers stack along the
a-axis with no specific interactions between them (ESI figure S13). Finally, for 11, the supra-
molecular array in the ac-plane is sustained by C–H. . .O and π. . .π interactions [between the
pyridyl and tolyl rings], figure S14(a), and these stack along the b-axis with no specific inter-
actions between them (ESI figure S14(b)).
4. Conclusions
A series of 12 cadmium compounds, [Cd(X2)(L)] (4, 10), [Cd(X2)(L)(DMSO)] (9), [Cd(X2)
(L)]2 (1–3, 5, 7, 8, 11, and 12), and [Cd(Cl2)2(L)]n (6), where X = chloride, bromide, and
iodide, and L = (E)-N-(pyridin-2-ylmethylidene)arylamine, were characterized. The CdBr2
and CdI2 compounds with L were usually binuclear unless additional donors on L or

Diimine cadmium dihalides
117
solvent were able to coordinate with cadmium. Dimerization was only averted when L car-
ries an oxygen donor capable of coordinating to cadmium or when coordinating solvent,
i.e. DMSO, was present. In all cases, a five-coordinate cadmium environment ensued.
While a binuclear structure was also observed for a sole CdCl2 derivative, a polymeric
structure with octahedral cadmium was found in one instance, i.e. [Cd(Cl2)2(L)]n (6), owing
to the presence of μ2-bridging chloro ligands, a result correlated to the presence of electro-
negative chloride coupled with a (relatively) strongly coordinating ligand, L. The detailed
analysis of the crystal packing revealed the presence of unusual C–H. . .π interactions where
the π-system is a chelate ring or a Cd2Br2 unit.
Supplementary material
CCDC numbers 913003–913014 contain the supplementary crystallographic data for 1–12.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Center, 12 Union Road, Cam-
bridge CB2 1EZ, UK; Fax:+44 1223 336 033; or Email: deposit@ccdc.cam.ac.uk.
Acknowledgements
The financial support of the University Grants Commission, New Delhi, India (Grant No. 42-
396/2013 (SR), TSBB) and that from the University Grants Commission, New Delhi, India
through SAP-DSA, Phase-III are gratefully acknowledged. Support from the Ministry of Higher
Education, Malaysia, High-Impact Research scheme (UM.C/HIR-MOHE/SC/03) is also grate-
fully acknowledged.
References
[1] C. Bianchini, G. Giambastiani, I. Guerrero Rios, G. Mantovani, A. Meli, A.M. Segarra. Coord. Chem. Rev.,
250, 1391 (2006).
[2] C. Bianchini, D. Gatteschi, G. Giambastiani, I. Guerrero Rios, A. Ienco, F. Laschi, C. Mealli, A. Meli,
L. Sorace, A. Toti, F. Vizza. Organometallics, 26, 726 (2007).
[3] C. Bianchini, G. Giambastiani, I. Guerrero Rios, A. Meli, A.M. Segarra, A. Toti, F. Vizza. J. Mol. Catal. A:
Chem., 277, 40 (2007).
[4] C. Bianchini, G. Giambastiani, G. Mantovani, A. Meli, D. Mimeau. J. Organomet. Chem., 689, 1356 (2004).
[5] C. Bianchini, G. Mantovani, A. Meli, F. Migliacci. Organometallics, 22, 2545 (2003).
[6] A. Toti, G. Giambastiani, C. Bianchini, A. Meli, L. Luconi. Adv. Synth. Catal., 350, 1855 (2008).
[7] C. Bianchini, G. Giambastiani, L. Luconi, A. Meli. Coord. Chem. Rev., 254, 431 (2010).
[8] H. Chun, H. Jung. Inorg. Chem., 48, 417 (2009).
[9] A. Kuc, T. Heine, G. Seifert, H.A. Duarte. Chem. Eur. J., 14, 6597 (2008).
[10] S.Y. Lee, S. Park, H.J. Kim, J.H. Jung, S.S. Lee. Inorg. Chem., 47, 1913 (2008).
[11] E. Shyu, R.M. Supkowski, R.L. LaDuca. Inorg. Chem., 48, 2723 (2009).
[12] S. Takizawa, H. Somei, D. Jayaprakash, H. Sasai. Angew. Chem. Int. Ed., 42, 5711 (2003).
[13] S.J. Hong, J.Y. Ryu, J.Y. Lee, C. Kim, S.-J. Kim, Y. Kim. J. Chem. Soc., Dalton Trans., 2697 (2004).
[14] S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki, Y. Kinoshita, S. Kitagawa. J. Am. Chem.
Soc., 129, 2607 (2007).
[15] D.N. Dybtsev, A.L. Nuzhdin, H. Chun, K.P. Bryliakov, E.P. Talsi, V.P. Fedin, K. Kim. Angew. Chem. Int. Ed.,
45, 916 (2006).
[16] G.A. Mines, B.-C. Tzeng, K.J. Stevenson, J. Li, J.T. Hupp. Angew. Chem. Int. Ed., 41, 154 (2002).
[17] A. Lan, K. Li, H. Wu, D.H. Olson, T.J. Emge, W. Ki, M. Hong, J. Li. Angew. Chem. Int. Ed., 48, 2334
(2009).
[18] L.-G. Qiu, Z.-Q. Li, Y. Wu, W. Wang, T. Xu, X. Jiang. Chem. Commun., 3642 (2008).
[19] T. Gadzikwa, B.-S. Zeng, J.T. Hupp, S.T. Nguyen. Chem. Commun., 3672 (2008).

118
T.S. Basu Baul et al.
[20] M.A. Withersby, A.J. Blake, N.R. Champness, P.A. Cooke, P. Hubberstey, W.-S. Li, M. Schroder. Inorg.
Chem., 38, 2259 (1999).
[21] J. Yang, J.-F. Ma, Y.-Y. Liu, J.-C. Ma, S.R. Batten. Cryst. Growth Des., 9, 1894 (2009).
[22] Y.J. Lee, E.Y. Kim, S.H. Kim, S.P. Jang, T.G. Lee, C. Kim, S.-J. Kim, Y. Kim. New J. Chem., 35, 833 (2011).
[23] Z. Lin, M.-L. Tong. Coord. Chem. Rev., 255, 421 (2010).
[24] A.J. Blake, N.R. Brooks, N.R. Champness, P.A. Cooke, A.M. Deveson, D. Fenske, P. Hubberstey, M.J. Schroder.
J. Chem. Soc., Dalton Trans., 2103 (1999).
[25] Y.-Q. Huang, X.-Q. Zhao, W. Shi, W.-Y. Liu, Z.-L. Chen, P. Cheng, D.-Z. Liao, S.-P. Yan. Cryst. Growth
Des., 8, 3652 (2008).
[26] H. Kwak, S.H. Lee, S.H. Kim, Y.M. Lee, E.Y. Lee, B.K. Park, E.Y. Kim, C. Kim, S.-J. Kim, Y. Kim. Eur. J.
Inorg. Chem., 408 (2008).
[27] R. Mondal, T. Basu, D. Sadhukhan, T. Chattopadhyay, M. Bhunia. Cryst. Growth Des., 9, 1095 (2009).
[28] G.R. Desiraju. Acc. Chem. Res., 35, 565 (2002).
[29] H.W. Roesky, M. Andruh. Coord. Chem. Rev., 236, 91 (2003).
[30] X.J. Luan, Y.-Y. Wang, D.-S. Li, P. Liu, H.-M. Hu, Q.-Z. Shi, S.-M. Peng. Angew. Chem. Int. Ed., 44, 3864
(2005).
[31] B.-B. Ding, Y.-Q. Weng, Z.-W. Mao, C.-K. Lam, X.-M. Chen, B.-H. Ye. Inorg. Chem., 44, 8836 (2005).
[32] C. Janiak. J. Chem. Soc., Dalton Trans., 2781 (2003).
[33] C. Hu, Q. Li, U. Englert. CrystEngComm, 4, 20 (2002).
[34] C. Hu, Q. Li, U. Englert. CrystEngComm, 5, 519 (2003).
[35] H.M. Park, I.H. Hwang, J.M. Bae, Y.D. Jo, C. Kim, H.-Y. Kim, Y. Kim, S.-J. Kim. Bull. Korean Chem. Soc.,
33, 1517 (2012).
[36] H.-X. Guo, H.-B. Lin, Q.-H. Wang. Acta Crystallogr., Sect. E, 62, m1239 (2006).
[37] C. Janiak, S. Deblon, H.-P. Wu, M.J. Kolm, P. Klüfers, H. Piotrowski, P. Mayer. Eur. J. Inorg. Chem., 1507
(1999).
[38] H.-Y. He, Y.-L. Zhou, J. Chen, L.-G. Zhu. Z. Kristallogr. New Cryst. Struct., 220, 209 (2005).
[39] J. Sun, X. Tong, H. Xu. Inorg. Chem. Commun., 13, 645 (2010).
[40] H. Wang, R.-G. Xiong, H.-Y. Chen, X.-Y. Huang, X.-Z. You. Acta Crystallogr., Sect. C, 52, 1658 (1996).
[41] Y.-H. Sun, S.-F. Luo, X.-Z. Zhang, Z.-Y. Du. Acta Crystallogr., Sect. E, 65, m708 (2009).
[42] N. Kundu, D. Mandal, M. Chaudhury, E.R.T. Tiekink. Appl. Organomet. Chem., 19, 1268 (2005).
[43] Z.R. Ranjbar, A. Morsali, L.-G. Zhuz. J. Coord. Chem., 60, 667 (2007).
[44] W. Zhang, Z. Jiang, L. Lu. Acta Crystallogr., Sect. E, 65, m7 (2009).
[45] K.-L. Zhong. Acta Crystallogr., Sect. E, 67, m1609 (2011).
[46] J.-M. Shi, J.-N. Chen, L.-D. Liu. Acta Crystallogr., Sect. E, 62, m2094 (2006).
[47] (a) T.S. Basu Baul, S. Kundu, S. Mitra, H. Höpfl, E.R.T. Tiekink, A. Linden. Dalton Trans., 1905 (2013);
(b) T.S. Basu Baul, S. Kundu, H. Höpfl, E.R.T. Tiekink, A. Linden. Polyhedron, 55, 270 (2013).
[48] CrysAlisPro (Version 1.171.33.55), Agilent Technologies, Yarnton, Oxfordshire, England (2010).
[49] G.M. Sheldrick. Acta Crystallogr., Sect. A, 64, 112 (2008).
[50] L.J. Farrugia. J. Appl. Crystallogr., 45, 849 (2012).
[51] A.L. Spek. Acta Crystallogr., Sect. D, 65, 148 (2009).
[52] K. Brandenburg. DIAMOND, Crystal Impact GbR, Bonn, Germany (2006).
[53] S.S. Tandon, S. Chander, L.K. Thompson. Inorg. Chim. Acta, 300–302, 683 (2000).
[54] K. Nakamoto. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York
(1986).
[55] G. Mahmoudi, A. Morsali. Polyhedron, 27, 1070 (2008).
[56] P. Biscarini, L. Fusina, G.D. Nivellini. J. Chem. Soc., Dalton Trans., 1003 (1972).
[57] K. Nakamoto. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, 6th Edn,
Wiley, Hoboken, NJ (2009).
[58] (a) S.R. Li, L. Xu. Inorg. Chem., 44, 3731 (2005); (b) J. Lu, K. Zhao, Q.R. Fang, J.Q. Xu, J.H. Yu, X. Zhang,
H.Y. Bie, T.G. Wang. Cryst. Growth Des., 5, 1091 (2005); (c) L. Wang, M. Yang, G.H. Li, Z. Shi, S.H. Feng.
Inorg. Chem., 45, 2474 (2006); (d) K.L. Huang, Y.T. He, M. Huang. J. Coord. Chem., 61, 2735 (2008);
(e) Y.L. Yao, L. Xue, Y.X. Che, J.M. Zheng. Cryst. Growth Des., 9, 606 (2009); (f) B. Liu, Y.C. Qiu, G. Peng,
L. Ma, L.M. Jin, J.B. Cai, H. Deng. Inorg. Chem. Commun., 12, 1200 (2009).
[59] C.-C. Ji, L. Qin, Y.-Z. Li, Z.-J. Guo, H.-G. Zheng. Cryst. Growth Des., 11, 480 (2011).
[60] (a) A. Saha Roy, M.K. Biswas, T. Weyhermüller, P. Ghosh. Dalton Trans., 146 (2011); (b) A. Saha Roy,
P. Saha, P. Mitra, S.S. Maity, S. Ghosh, P. Ghosh. Dalton Trans., 7375 (2011).
[61] A. Chakrabarty, S. Kar, D.N. Nath, N. Guchhait. J. Phys. Chem. A, 110, 12089 (2006).
[62] S. Mahanta, R.B. Singh, S. Kar, N. Guchhait. J. Photochem. Photobiol., A, 194, 318 (2008).
[63] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor. J. Chem. Soc., Dalton Trans., 1349 (1984).
[64] F.H. Allen. Acta Crystallogr., Sect. B, 58, 380 (2002).
[65] K. Wurst, M.R. Buchmeiser. Heterocycl. Commun., 5, 37 (1999).

Diimine cadmium dihalides
119
[66] (a) M. Schulz, M. Klopfleisch, H. Gorls, M. Kahnes, M. Westerhausen. Inorg. Chim. Acta, 362, 4706 (2009);
(b) J.J. Braymer, J.-S. Choi, A.S. DeToma, C. Wang, K. Nam, J.W. Kampf, A. Ramamoorthy, M.H. Lim.
Inorg. Chem., 50, 10724 (2011).
[67] M.F. Nejad, M.R.T.B. Olyai, H.R. Khavasi. Z. Kristallogr., New Cryst. Struct., 225, 717 (2010).
[68] P.K. Bhaumik, S. Jana, S. Chattopadhyay. Inorg. Chim. Acta, 390, 167 (2012).
[69] D.K. Seth, S. Bhattacharya. Polyhedron, 30, 2438 (2011).
[70] S. Reinhardt, K. Heinze. Z. Anorg. Allg. Chem., 632, 1465 (2006).
[71] S. Dehghanpour, A. Mahmoudi, S. Rostami. Polyhedron, 29, 2190 (2010).
[72] (a) H. Masui. Coord. Chem. Rev., 219–221, 957 (2001); (b) Y.Z. Wang, G.H. Robinson. Organometallics, 26,
2 (2007).
[73] (a) Z.D. Tomić, D.N. Sredojević, S.D. Zarić. Cryst. Growth Des., 6, 29 (2006); (b) D.N. Sredojević,
Z.D. Tomić, S.D. Zarić. Cryst. Growth Des., 10, 3901 (2010).
[74] E.R.T. Tiekink. In Crystal Engineering in Supramolecular Chemistry: From Molecules to Nanomaterials,
J.W. Steed, P.A. Gale (Eds.), pp. 2791–2828, John Wiley & Sons, Chichester (2012).
[75] (a) M.K. Milčič, V.B. Medaković, D.N. Sredojević, N.O. Juranić, S.D. Zarić. Inorg. Chem., 45, 4755 (2006);
(b) E.R.T. Tiekink, J. Zukerman-Schpector. Chem. Commun., 47, 6623 (2011).
[76] A. Gavezzotti. CrystEngComm, 15, 4027 (2013).