Mono, di and trinuclear photo-luminescent cadmium(II) complexes with N2O and N2O2 donor salicylidimine Schiff bases: Synthesis, structure and self assembly

Article abstract of DOI:10.1016/j.ica.2015.04.018

Four new octahedral cadmium(II) complexes, [(Cd)(L¹)(HL¹)](ClO₄) (1), [Cd₂(L²)₂(SCN)₂(CH₃OH)₂] (2), [(CdL³)₃(μ-1,1,1-OH)](ClO₄

Full text of DOI:10.1016/j.ica.2015.04.018

Inorganica Chimica Acta 433 (2015) 72–77
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Mono, di and trinuclear photo-luminescent cadmium(II) complexes with
N2O and N2O2 donor salicylidimine Schiff bases: Synthesis, structure and
self assembly
⇑
Sumit Roy, Shouvik Chattopadhyay
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Four new octahedral cadmium(II) complexes, [(Cd)(L1)(HL1)](ClO4) (1), [Cd2(L2)2(SCN)2(CH3OH)2] (2),
Article history:
[(CdL3)3( -1,1,1-OH)](ClO4)2 (3) and [Cd2(L4)2(SCN)(NO3)] (4) have been synthesized using four Schiff
l
Received 9 January 2015
Received in revised form 4 March 2015
Accepted 10 April 2015
bases, HL1, HL2, HL3 and HL4, (where HL1 = 2-(2-(ethylamino)ethyliminomethyl)phenol, HL2 = 2-(2-
(dimethylamino)ethyliminomethyl)-4-bromophenol,
HL3 = 2-(2-(diethylamino)ethyliminomethyl)-6-
Available online 27 April 2015
methoxyphenol and HL4 = 2-(2-(ethylamino)ethyliminomethyl)-6-methoxyphenol). All four complexes
have been characterized by elemental and spectral analysis and structures have been confirmed by single
crystal X-ray diffraction studies. Complex 1 is a mononuclear cationic bis-ligand complex. Complex 2 fea-
tures a double end-to-end thiocyanate bridged dinuclear cadmium(II) complex. Complex 3 has a partial
cubane [Cd3O4] core in which three [CdL3] subunits are interconnected through two types of oxygen
bridges afforded by phenoxo oxygen atoms of ligands and a central hydroxo group. Complex 4 has a dou-
ble phenoxo bridged dinuclear structure. Supramolecular interactions in all four complexes were also
explored. All four complexes show fluorescence.
Keywords:
Cadmium(II)
Schiff base
Crystal structure
Photolumiscence
Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction
architectures with the change in denticity of Schiff base ligands
and with the presence of different co-ligands in the reaction med-
The chemistry of the metal Schiff base complexes has been paid
considerable attention since long and it is still a promising area of
research [1–10]. Among different Schiff bases, N2O donor salicy-
lidimine Schiff bases [11–13], have widely been used by several
groups to form different homo and hetero polynuclear complexes
with several transition and non-transition metal ions [14–20]. On
the other hand, there have been immense interests in studying
supra-molecular structures [21]. The molecular and crystalline
architectures of the complexes are modulated by hydrogen bond-
ium. Herein, we would like to report the synthesis, characteriza-
tion, crystal structures, supramolecular architectures and
fluorescence properties of four new cadmium(II) Schiff base
complexes.
2. Experimental
All starting materials and solvents were commercially available,
reagent grade, and used as purchased from Sigma–Aldrich without
further purification.
ing [22–26] as well as
pꢀ ꢀ ꢀ
p, C–Hꢀ ꢀ ꢀ
p
and anionꢀ ꢀ ꢀ
p interactions
[27–29]. In the present work, we have used four different Schiff
bases, produced by the condensation of N-substituted-1,2-di-
aminoethane and salicylaldehyde or its derivatives, to form
cadmium(II) complexes. We have selected cadmium(II) as the
metal centre for its ability to exhibit varieties of geometries as a
result of its d10 electronic configuration with no CFSE in any crystal
field, steric requirements of ligands controlling the geometries and
coordination numbers [30–32]. Our intension was to examine the
changes, if any, in their crystalline and supra-molecular
Caution!!!: Perchlorate salts are potentially explosive. Although
no problem was encountered in the present study, only small
amounts of the materials should be prepared and they must be
handled with care.
2.1. Preparations
2.1.1. Preparation of ligands
2.1.1.1. Synthesis of HL1 {2-(2-(ethylamino)ethyliminomethyl)
phenol}. The tridentate schiff base, HL1, was prepared by refluxing
N-ethyl-1,2-diaminoethane (1 mmol, 0.105 mL) with salicylalde-
hyde (1 mmol, 0.104 mL) in methanol solution (20 mL) for ca.
⇑
Corresponding author.
http://dx.doi.org/10.1016/j.ica.2015.04.018
0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

S. Roy, S. Chattopadhyay / Inorganica Chimica Acta 433 (2015) 72–77
73
1 h. Methanol was evaporated under reduced pressure to get HL1
as yellow oily liquid. It was not purified and used directly for the
preparation of complex 1.
2974–2864
(
m
CH); UV–Vis, kmax (nm),
[
emax (L molꢁ1 cmꢁ1)]
(DMSO), 264 (1.5 ꢂ 104), 332 (3.4 ꢂ 103).
IR (KBr, cmꢁ1): 1636 (
mC@N), 2968–2846 (mCH), 3308 (mOH).
2.1.1.8. Synthesis of [Cd2(L4)2(SCN)(NO3)] (4). A methanol solution of
cadmium(II) nitrate tetrahydrate (1 mmol, 0.308 g) was added to
the methanol solution of the Schiff base and refluxed for 1 h. A
methanol solution of sodium thiocyanate (0.5 mmol, 0.04 g) was
then added to it and refluxed further for ca. 1 h. X-ray quality sin-
gle crystals of complex 4 were obtained after few days on slow
evaporation of the solution in open atmosphere.
2.1.1.2. Synthesis of HL2 {2-(2-(dimethylamino)ethyliminomethyl)-4-
bromophenol}. The tridentate schiff base, HL2, was prepared by
refluxing N,N-dimethyl-1,2-diaminoethane (1 mmol, 0.105 mL)
with 5-bromosalicylaldehyde (1 mmol, 0.201 g) in methanol solu-
tion (20 mL) for ca. 1 h. Methanol was evaporated under reduced
pressure to get HL2 as yellow oily liquid. 1 h. It was not purified
and used directly for the preparation of complex 2.
Yield: 0.49 g (63%). Anal. Calc. for C25H32Cd2N6O7S (FW 785.46):
C, 38.23; H, 4.11; N, 10.70. Found: C, 38.17; H, 4.07; N, 10.79%. IR
IR (KBr, cmꢁ1): 1635 (
mC@N), 2971–2820 (mCH), 3455 (mOH).
(KBr, cmꢁ1): 1633 (
mC@N), 2074 (mSCN), 3200 (mNH), 1451, 1295,
1082 (mNO3), 2909–2808 (m
CH); UV–Vis, kmax (nm), [emax (L molꢁ1
2.1.1.3. Synthesis of HL3 {2-(2-(diethylamino)ethyliminomethyl)-6-
methoxyphenol}. The tetradentate schiff base, HL3, was prepared by
refluxing N,N-diethyl-1,2-diaminoethane (1 mmol, 0.140 mL) with
3-methoxysalicylaldehyde (1 mmol, 0.152 g) in methanol solution
(20 mL) for ca. 1 h. Methanol was evaporated under reduced pres-
sure to get HL1 as yellow oily liquid. It was not purified and used
directly for the preparation of complex 3.
cmꢁ1)] (DMSO), 267 (1.8 ꢂ 104), 323 (5.9 ꢂ 103).
2.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a PerkinElmer 240C elemental analyzer. Infrared spectra
in KBr (4000–400 cmꢁ1
) were recorded using a PerkinElmer
IR (KBr, cmꢁ1): 1632 (
mC@N), 2965–2831 (mCH), 3415 (mOH).
Spectrum Two FTIR spectrophotometer. Electronic spectra in
DMSO (800–200 nm) were recorded on a PerkinElmer Lambda 35
UV–Vis spectrophotometer. Fluorescence spectra in DMSO were
obtained on a Hitachi F-7000 Fluorescence spectrophotometer at
room temperature. Lifetime measurements were recorded using
Hamamatsu MCP photomultiplier (R3809) and were analyzed by
using IBHDAS6 software. The powder XRD data was collected on
2.1.1.4. Synthesis of HL4 {2-(2-(ethylamino)ethyliminomethyl)-6-
methoxyphenol}. It was prepared in a method similar to that for
the ligand, HL1, except that 3-methoxysalicylaldehyde (0.152 g,
1 mmol) was used instead of salicylaldehyde. Methanol was evap-
orated under reduced pressure to get HL4 as yellow oily liquid. It
was not purified and used directly for the preparation of complex
4.
a Bruker D8 Advance X-ray diffractometer using Cu K
a radiation
(k = 1.548 Å) generated at 40 kV and 40 mA. The PXRD spectrum
was recorded in a 2h range of 5–50° using 1-D Lynxeye detector
at ambient conditions.
IR (KBr, cmꢁ1): 1635 (
mC@N), 2964–2838 (mCH), 3471 (mOH).
2.1.1.5. Synthesis of [(Cd)(L1)(HL1)](ClO4) (1). A methanol solution of
cadmium(II) perchlorate hexahydrate (0.5 mmol, 0.210 g) was
added to the methanol solution of the Schiff base and refluxed
for 1 h. X-ray quality single crystals of complex 1 were obtained
after few days on slow evaporation of the solution in open
atmosphere.
2.3. X-ray crystallography
Single crystals of four complexes having suitable dimensions,
were used for data collection using a Bruker SMART APEX II diffrac-
tometer equipped with graphite-monochromated Mo Ka radiation
(k = 0.71073 Å) at 293 K. Molecular structures were solved using
the SHELX-97 package [33]. Non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms, attached to oxy-
gen and nitrogen, were located by difference Fourier maps and
were kept at fixed positions. All other hydrogen atoms were placed
in their geometrically idealized positions and constrained to ride
on their parent atoms. Multi-scan empirical absorption corrections
were applied to the data using the program SADABS [34]. A summary
of the crystallographic data is given in Table 1.
Yield: 0.40 g (68%). Anal. Calc. for C22H31CdN4ClO6 (FW 595.37):
C, 44.38; H, 5.25; N, 9.41. Found: C, 44.34; H, 5.19; N, 9.48%. IR
(KBr, cmꢁ1): 1634 (
mC@N), 3271 (mNH), 1100 (mClO4), 2972–2861
(m
CH). UV–Vis, kmax (nm), [emax (L molꢁ1 cmꢁ1)] (DMSO), 263
(1.3 ꢂ 104), 326 (8.9 ꢂ 103).
2.1.1.6. Synthesis of [Cd2(L2)2(
l-1,3-SCN)2(CH3OH)2] (2). A methanol
solution of cadmium(II) nitrate tetrahydrate (1 mmol, 0.308 g) was
added to the methanol solution of the Schiff base and refluxed for
1 h. A methanol solution of sodium thiocyanate (1 mmol, 0.081 g)
was then added to it and refluxed further for ca. 1 h. X-ray quality
single crystals of complex 2 were obtained after few days on slow
evaporation of the solution in open atmosphere.
3. Results and discussion
Yield: 0.69 g (73%). Anal. Calc. for C26H36Br2Cd2N6O4S2 (FW
945.35): C, 33.03; H, 3.84; N, 8.89. Found: C, 32.94; H, 3.77; N,
3.1. Synthesis
8.95%. IR (KBr, cmꢁ1): 1633 (
m
C@N), 2111, 2076 (
m
SCN), 3436 (
m
OH),
Reaction of the Schiff base (HL1) with cadmium(II) perchlorate
hexahydrate produces complex 1. Use of perchlorate increases
the [H+] of the medium (0.0158 M) and may be responsible
for the non-deprotonation of one of the Schiff bases present
in complex 1. Literature shows that there is only one report
of the solid state structure of similar bis-ligand complex of
cadmium(II), [Cd(L)(HL)]ClO4 {HL = 2-(2-(dimethylamino)ethylim-
inomethyl)phenol} with a similar ligand [12]. This compound
was also prepared using cadmium(II) perchlorate. Thiocyante
bridged dinuclear complex (2) was prepared by the reaction of
HL2 with cadmium(II) nitrate tetrahydrate. There is only one report
of thiocynate bridged dinuclear cadmium complex with similar
N2O donor Schiff base [35]. Reaction of cadmium(II) perchlorate
2998–2840
(
m
CH); UV–Vis, kmax (nm),
[e
max(L molꢁ1 cmꢁ1)]
(DMSO), 262 (9.3 ꢂ 104), 337 (8.2 ꢂ 103).
2.1.1.7. Synthesis of [(CdL3)3(
l-1,1,1-OH)](ClO4)2 (3). A methanol
solution of cadmium(II) perchlorate hexahydrate (1 mmol,
0.419 g) was added to the methanol solution of the Schiff base
and refluxed for 1 h. X-ray quality single crystals of complex 3
were obtained after few days on slow evaporation of the solution
in open atmosphere.
Yield: 0.81 g (63%). Anal. Calc. for C42H64Cd3N6Cl2O15 (FW
1301.12): C, 38.77; H, 4.96; N, 6.46. Found: C, 38.71; H, 4.92; N,
6.53%. IR (KBr, cmꢁ1): 1081 (
mClO4), 1630 (mC@N), 3535 (mOH),

74
S. Roy, S. Chattopadhyay / Inorganica Chimica Acta 433 (2015) 72–77
Table 1
Crystal data and refinement details of complexes 1–4.
1
2
3
4
Formula
Formula weight
T (K)
C
22H31CdN4ClO6
C26H36Br2Cd2N6O4S2
945.35
293
C42H64Cd3N6O7Cl2O4
1301.12
293
C25H32Cd2N6O7S
785.46
293
595.37
293
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Orthorhombic
Pbna
Triclinic
P1
Trigonal
R-3
13.2748(3)
13.2748(3)
53.8944(19)
(90)
(90)
(120)
6
Triclinic
P1
ꢀ
ꢀ
12.9162(3)
18.7636(5)
21.5088(5)
(90)
(90)
(90)
8.4198(9)
9.0594(10)
11.9073(14)
109.818(5)
94.169(7)
91.729(6)
1
1.845
3.761
464
7.1649(2)
11.8337(3)
18.2588(4)
79.101(1)
87.382(7)
82.122(2)
2
1.733
1.534
784
a
(°)
b (°)
c
(°)
Z
8
Dcalc (g cmꢁ3
)
1.517
0.983
2432
1.576
1.315
3936
l
(mmꢁ1
F(000)
)
Total reflections
Unique reflections
Observed data[I > 2
No. of parameters
R(int)
75,054
4985
3669
306
0.042
9254
3262
2678
171
41,770
3510
2941
207
22,525
5730
4570
370
r(I)]
0.039
0.043
0.036
R1, wR2 (all data)
R1, wR2 [I > 2r(I)]
0.0643, 0.1414
0.0448, 0.1258
0.0669, 0.1452
0.0529, 0.1348
0.0550, 0.1556
0.0452, 0.1402
0.0437, 0.0803
0.0316, 0.0725
hexahydrate with HL3 produces a trinuclear complex, [(CdL3)3
-1,1,1-OH)](ClO4)2 (3). Formation of complex 3 is unique in the
sense that solid state characterization of any such partial cubane
cadmium(II) complex with N2O2 donor salicylidimine Schiff base
is not reported in literature.
anion. Cadmium(II) centre is in a hexa-coordinated octahedral
environment, being bonded to amine nitrogen atom, N(3), imine
nitrogen atom, N(4), and phenoxo oxygen atom, O(1), from one
deprotonated Schiff base ligand, (L1)ꢁ, and amine nitrogen atom,
N(1), imine nitrogen atom, N(2), and phenol oxygen atom, O(2),
of one protonated Schiff base ligand (HL1), respectively where both
ligands occupy facial positions. Cadmuim(II)–nitrogen bond
lengths range from 2.271(4) to 2.391(4) Å, as is also observed in
similar systems [12,39]. The saturated five membered chelate rings
Cd(1)–N(1)–C(14)–C(15)–N(2) and Cd(1)–N(3)–C(3)–C(4)–N(4)
present envelope conformations with puckering parameters
(l
On the other hand, addition of sodium thiocyanate to the
methanol solution of HL4 and cadmium(II) nitrate tetrahydrate
produced
a
double phenoxo bridged dinuclear complex,
[Cd2(L4)2(SCN)(NO3)] (4), in which nitrate and thiocyanate ions
are acting as co-ligands. Formation of complex 4 is also interesting
due to the presence of both nitrate and thiocyanate in the complex.
All related dinuclear cadmium(II) complexes, reported in literature,
contains two molecules of only one co-ligand, without exception
[20,36–38].
q(2) = 0.476(7) Å,
u
(2) = 68.8(6)°
and
q(2) = 0.473(6) Å,
u
(2) = 253.0(5)° respectively [40]. The hydrogen atom, H(2),
attached to phenol oxygen atom, O(2), forms a exceptionally strong
hydrogen bond (Fig. S1) with the symmetry related phenoxo
oxygen atom, O(1)a, {Symmetry transformation, a = x, 1/2 ꢁ y,
1 ꢁ z} of a neighbouring molecule. This is a very strong H bond
(Donorꢀ ꢀ ꢀAcceptor distance 2.45 Å) with respect the other reported
systems [15,28,47]. Selected bond angles are gathered in Table S1.
The details of other supramolecular interactions are described in
Electronic Supplementary Information.
3.2. Description of structures
3.2.1. [(Cd)(L1)(HL1)](ClO)4 (1)
Complex 1 crystallizes in orthorhombic space group Pbna. A
perspective view of the complex with selective atom-numbering
scheme is shown in Fig. 1. The asymmetric unit consists of a dis-
crete [(Cd)(L1)(HL1)]+ cation and one non-coordinated perchlorate
3.2.2. [Cd2(L2)2(
l-1,3-SCN)2(CH3OH)2] (2)
ꢀ
Complex 2 crystallizes in triclinic space group P1. It features a
hexa-coordinated double end-to-end thiocyanate bridged dinuclear
centrosymmetric cadmium(II) complex, as shown in Fig. 2. The dis-
torted octahedral cadmium(II) centre, Cd(1), is coordinated merid-
ionally by one phenoxo oxygen atom, O(1), one imine nitrogen
Fig. 2. Perspective view of complex 2 with selective atom-numbering scheme.
Hydrogen atoms are not shown for clarity. Selected bond lengths (Å): Cd(1)–N(1)
2.430(9), Cd(1)–N(2) 2.273(5), Cd(1)–S(1) 2.797(2), Cd(1)–N(3)b 2.218(6), Cd(1)–
O(1) 2.230(5), Cd(1)–O(2) 2.380(6). Symmetry transformation b = 2 ꢁ x, 1 ꢁ y, 2 ꢁ z.
Fig. 1. Perspective view of complex 1 with selective atom-numbering scheme.
Perchlorate anion and hydrogen atoms are not shown for clarity. Selected bond
lengths (Å): Cd(1)–N(1) 2.391(4), Cd(1)–N(2) 2.271(4), Cd(1)–N(3) 2.381(4), Cd(1)–
N(4) 2.285(4), Cd(1)–O(1) 2.314(3), Cd(1)–O(2) 2.330(3).

S. Roy, S. Chattopadhyay / Inorganica Chimica Acta 433 (2015) 72–77
75
atom, N(2), one amine nitrogen atom, N(1), from deprotonated Schiff
3.2.4. [Cd2(L4)2(SCN)(NO3)] (4)
base ligand, (L2)ꢁ, and one sulfur atom, S(1), of coordinated thio-
cyanate and one oxygen atom, O(2), from a coordinated methanol.
The sixth coordination site of the distorted octahedral cadmium(II)
is occupied by a symmetry related (2 ꢁ x, 1 ꢁ y, 2 ꢁ z) nitrogen
atom, N(3)b, of an thiocyanate to form a double end-to-end thio-
cyanate bridged dinuclear cadmium(II) complex. The Cd–O, Cd–S
and Cd–N distances fall within the range 2.218(5)–2.797(2) Å, as
were also observed in other complexes [35]. The saturated five
membered chelate ring Cd(1)–N(1)–C(3)–C(4)–C(5)–N(2) present
an envelope conformation, with puckering parameters
ꢀ
Complex 4 crystallizes in the triclinic space group P1. It fea-
tures a hexa-coordinated phenoxo bridged dinuclear cadmium(II)
complex, as shown in Fig. 4. Within the dinuclear unit, each
cadmium(II) centre is in a highly distorted pentagonal pyramidal
geometry. The amine nitrogen, the imine nitrogen, the phenoxy
oygen and the methoxy oxygen of the tetradentate deprotonated
Schiff base coordinates equatorially each cadmium(II). A phenoxo
oxygen atom from a second molecule of the Schiff base also coor-
dinates cadmium(II) equatorially. The apical position of Cd(1) is
occupied by a nitrate nitrogen atom and that of Cd(2) by a thio-
cyante nitrogen atom. The dinuclear bridging unit Cd2O2 describes
a rhombohedral plane. The rhombohedral angles are O(2)–Cd(1)–
O(1), 74.86(9)°, Cd(1)–O(1)–Cd(2), 102.48(9)°; O(1)–Cd(2)–O(2)
75.34(9)°, Cd(2)–O(2)–Cd(1), 105.2(1)°. The Cdꢀ ꢀ ꢀCd distance
within the dinuclear unit is 3.5327(4) Å. The saturated
five membered chelate rings Cd(1)–N(1)–C(3)–C(4)–N(2) and
Cd(2)–N(3)–C(15)–C(16)–N(4) present a half-chair conformation
q(2) = 0.356(11) Å,
u(2) = 257.8(13)° [40]. The bridging thio-
cyanates are quasi-linear; the S–C–N angle is 178.6°(7). The
Cdꢀ ꢀ ꢀCd distance within the dinuclear unit is 5.918(9) Å. Selected
bond angles are gathered in Table S2. The details of supramolecular
interactions are described in Electronic Supplementary Information.
3.2.3. [(CdL3)3(
Complex 3 comprises one cation, [(CdL3)3(
l-1,1,1-OH)](ClO4)2 (3)
-1,1,1-OH)]2+, which
with puckering parameters q(2) = 0.461(5) Å,
u(2) = 89.9(4)° and
l
q(2) = 0.546(4) Å, (2) = 227.7(4)° respectively [40]. Selected bond
u
has crystallographic 3-fold symmetry and two non-coordinated
perchlorate anions. A perspective view of the complex with
selected atom numbering scheme is shown in Fig. 3. The trinuclear
cation is comprised of three CdL3 subunits in which each
lengths and bond angles are gathered in Table 2 and Table S4,
respectively. The details of supramolecular interaction is described
in Electronic Supplementary Information.
cadmium(II) is coordinated to
a deprotonated tetradentate
monoanionic ligand (L3)ꢁ. The subunits are held together by two
distinct bridging systems: (i) the oxygen atom (O3) of a triply
bridging hydroxo group, capping the three cadmium(II) centres
and (ii) the bridging phenoxo oxygen atom from a symmetry
related adjacent ligand molecule. The three cadmium(II) and the
bridging hydroxo group form a flattened trigonal pyramid, with
the cadmium(II) falling at the corners of equilateral sides
(3.53(8) Å) and angles (60.00(1)°). The face-capping oxygen atom
(O3) is located at 1.021 Å above the plane defined by the Cd3 trian-
gle. The presence of Cd3OH is confirmed by (a) the location of the
hydrogen atom at the expected position in the final difference
Fourier map, (b) the electroneutrality of the crystal, and (c) the
refined Cd–O(H) distances and Cd–O(H)–Cd angles, which agree
well with a roughly tetrahedral or pseudo-tetrahedral sphere of
Cd, Cd, Cd, H species around the oxygen atom. The average bond
lengths in the octahedral coordination sphere are Cd–N(amine)
3.3. Powder X-ray diffraction
The experimental powder XRD patterns of bulk product of all
four complexes are in good agreement with simulated XRD pat-
terns from single crystal X-ray diffraction, confirming purity of
bulk materials. Simulated patterns were calculated from the single
crystal structural data (cif file) using CCDC Mercury software. Fig. 5
shows the experimental and simulated powder XRD patterns of
2.409 Å,
Cd–N(imine)
2.259 Å,
Cd–O(phenoxo)
2.213 Å,
Cd–O(methoxy) 2.613 Å, Cd–O(hydroxide) 2.284 Å, which are close
to those in other related Cd(II) compounds [41]. Selected bond
angles are gathered in Table S3. The details of hydrogen bonding
interaction is described in Electronic Supplementary Information.
Fig. 4. Perspective view of complex 4 with selective atom-numbering scheme.
Hydrogen atoms are not shown for clarity.
Table 2
Selected bond lengths (Å) of complex 4.
4
Cd(1)–N(1)
Cd(1)ꢁN(2)
Cd(1)ꢁO(1)
Cd(1)–O(2)
Cd(1)–O(3)
Cd(1)–O(4)
Cd(2)–O(1)
Cd(2)–O(2)
Cd(2)–N(3)
Cd(2)–N(4)
Cd(2)–N(6)
2.327(4)
2.285(3)
2.315(2)
2.184(2)
2.316(3)
2.691(3)
2.214(2)-
2.264(2)
2.313(4)
2.327(4)
2.250(4)
Fig. 3. Perspective view of complex 3 with selective atom-numbering scheme. Only
relevant atoms are shown. Hydrogen bonding interaction is shown in dotted line.
Selected bond lengths (Å): Cd(1)–N(1) 2.409(5) Cd(1)–N(2) 2.259(7), Cd(1)–O(1)
2.233(4), Cd(1)–O(1)d 2.194(5), Cd(1)–O(3) 2.284(2), Cd(1)–O(2)d 2.613(4).
Symmetry transformation, d = 1 ꢁ x + y, 1 ꢁ x, z.

76
S. Roy, S. Chattopadhyay / Inorganica Chimica Acta 433 (2015) 72–77
Fig. 5. Experimental and simulated powder XRD patterns of the complex 1,
confirming the purity of the bulk materials.
Fig. 6. Lifetime decay profile of complexes 1–4.
due to the reduction of double bond characters of the C@N bonds,
caused by the coordination of nitrogen atoms to the cadmium(II)
centers and are in agreement with results obtained from other sim-
ilar complexes described previously [37]. Positions of bands corre-
sponding to C–O stretching vibrations in free ligands also shift
towards lower frequency region in complexes due to participation
of the oxygen atoms in coordination [46]. At the same time, new
bands in the region of 480 cmꢁ1 arise in the complexes indicating
cadmium(II)–O vibrations. IR spectra of ligands and complexes are
given in Figs. S10–S17, {Electronic Supplementary Information}.
Electronic spectra of complexes and ligands are recorded in
DMSO solution in the range 200–800 nm. Absorption spectra of
ligands exhibit four bands, of which first two bands around 225
complex 1. The experimental and simulated powder XRD patterns
of complexes 2–4 are given in Figs. S7–S9, {Electronic
Supplementary Information}.
3.4. IR, electronic and fluorescence spectra
In IR spectra of all four complexes, distinct bands due to azome-
thine (C@N) groups within the range of 1630–1634 cmꢁ1 are rou-
tinely noticed. Sharp bands at 3271 and 3200 cmꢁ1 in IR spectra
of complexes 1 and 4 are assigned as N–H stretching vibrations.
End-to-end bridging mode of thiocyanate groups in 2 is confirmed
by the splitting of absorption band corresponding to SCN-stretch-
ing vibration appearing at 2111 and 2076 cmꢁ1 (indicating S- and
N- coordination modes respectively) [42]. In addition, two medium
and 260 nm may be attributed to
p–
p⁄ transitions and the two
bands at around 325 and 420 nm may be assinged as n-p⁄ transi-
tions [47]. Although same trends are observed in the complexes,
complexation leads to slight shifts in the positions of these bands.
Intense absorption bands are observed around 260 and 330 nm for
each of four complexes. There is no bands corresponding to d–d
electronic transitions as expected for cadmium(II) complexes with
d10 electronic configurations [41].
bands are observed at 822 and 794 cmꢁ1 related to
m(CS) [43,44].
On the other hand, appearance of strong bands in the range of
1080-1100 cmꢁ1 in IR spectra of 1 and 3 indicates the presence
of ionic perchlorates. Broad bands at 3436 and 3535 cmꢁ1 are
assigned as OH stretching vibrations in IR spectra of complexes 2
and 3 respectively. A distinct band at 2074 cmꢁ1 is indicative of
the presence of the N-coordinated thiocyanate in the IR spectrum
of complex 4. Monodentate nitrate exhibits three NO stretching
bands, mas(NO2) (B2), ms(NO2) (A1) and m(NO) (A1), as expected for its
C2v symmetry [45]. In complex 4, three sharp bands at 1451,
1295 and 1082 cmꢁ1 indicate the presence of unidentate coordina-
tion of NO3 ion, as is also substantiated by the X-ray single crystal
structure analysis. The bands in the range of 2998–2840 cmꢁ1 due
to alkyl C–H bond stretching vibrations are customarily noticed in
the IR spectra of all four complexes. The IR spectra of the com-
plexes have also been compared with those of the free ligands in
order to determine the coordination sites that may get involved
in chelation. The (C@N) stretching vibration in the free ligands
are shifted to lower frequency in the complexes. Theses shifts are
All four complexes exhibit luminescence in DMSO medium. On
exciting at 326, 337, 332 and 323 nm, emissions are observed at
420, 419, 420 and 416 nm for complexes 1, 2, 3 and 4 respectively.
Emission of the complexes is tentatively attributed to the intra-li-
gand transitions modified by metal coordination. Fluorescence life-
times of complexes are investigated in DMSO solution at room
temperature. Lifetimes of 1, 2, 3 and 4 are about 8.66, 7.80, 10.50
and 8.16 ns (Table 3) respectively, which are similar to other
cadmium(II) complexes [48]. Decay profiles (Fig. 6) were fitted to
a multi-exponential model:
ꢀ
ꢁ
X
ꢁt
IðtÞ ¼
ai exp
si
i
Table 3
The details data of the photoluminescence and time-resolved photoluminescence decays of complexes 1–4.
Complex
kex (nm)
kem (nm)
A1 (%)
s1 (ns)
A2 (%)
s2 (ns)
A3 (%)
s3 (ns)
sav (ns)
v2
1
2
3
4
326
337
332
323
420
419
420
416
35.23
33.30
16.75
33.42
3.38
2.98
3.16
3.28
47.08
44.55
74.26
48.51
15.67
15.16
13.35
15.64
17.69
22.15
8.98
0.55
0.49
0.49
0.48
8.66
7.80
10.50
8.16
1.1069
1.0980
1.1115
1.1167
18.08

S. Roy, S. Chattopadhyay / Inorganica Chimica Acta 433 (2015) 72–77
77
[6] S. Basak, S. Sen, S. Banerjee, S. Mitra, G. Rosair, M.T.G. Rodriguez, Polyhedron 26
(2007) 5104.
[7] S. Mukherjee, P.S. Mukherjee, Cryst. Growth Des. 14 (2014) 4177.
[8] C. Biswas, M.G.B. Drew, E. Ruiz, M. Estrader, C. Diaz, A. Ghosh, Dalton Trans. 39
(2010) 7474.
[9] S. Kundu, S. Roy, K. Bhar, R. Ghosh, C.-H. Lin, J. Ribas, B.K. Ghosh, J. Mol. Struct.
1038 (2013) 78.
[10] P. Chakraborty, A. Guha, S. Das, E. Zangrando, D. Das, Polyhedron 49 (2013) 12.
[11] A. Bhattacharyya, K. Harms, S. Chattopadhyay, Inorg. Chem. Commun. 48
(2014) 12.
where, tri-exponential functions are used to fit the emission of all
complexes with and obtaining
2 close to 1. The intensity-averaged
av) are determined using the following equation:
v
life times (
s
P
iais2i
iaisi
P
sam
¼
where, ai and si are the pre-exponential factor and excited-state
luminescence decay time associated with the i-th component,
respectively.
[12] H.-C. Fang, X.-Y. Yi, Z.-G. Gu, G. Zhao, Q.-Y. Wen, J.-Q. Zhu, A.-W. Xu, Y.-P. Cai,
Cryst. Growth Des. 9 (2009) 3776.
[13] A.A. Hoser, W. Schilf, A.S. Chełmieniecka, B. Kołodziej, B. Kamien´ ski, E. Grech,
The relative fluorescence quantum yields for all complexes
were measured in DMSO using quinine sulfate (in 0.5 (M) H2SO4,
/ = 0.54) as the quantum yield standard [49]. The fluorescence
quantum yields of complexes 1, 2, 3 and 4 are 0.00274, 0.0330,
0.00549 and 0.00515, respectively.
´
K. Wozniak, Polyhedron 31 (2012) 241.
[14] A. Bhattacharyya, P.K. Bhaumik, P.P. Jana, S. Chattopadhyay, Polyhedron 78
(2014) 40.
[15] S. Jana, B. Shaw, P. Bhowmik, K. Harms, M.G.B. Drew, S. Chattopadhyay, S.K.
Saha, Inorg. Chem. 53 (2014) 8723.
[16] C. Maxim, F. Tuna, A.M. Madalan, N. Avarvari, M. Andruh, Cryst. Growth Des.
12 (2012) 1654.
[17] P.K. Bhaumik, S. Chattopadhyay, Inorg. Chem. Commun. 22 (2012) 14.
[18] S. Bag, P.K. Bhaumik, S. Jana, M. Das, P. Bhowmik, S. Chattopadhyay,
Polyhedron 65 (2013) 229.
[19] P. Bhowmik, M. Corbella, N. Aliaga-Alcaldec, V. Gómezd, S. Chattopadhyay,
Polyhedron 49 (2013) 269.
[20] H.-C. Fang, Y.-Y. Ge, Y. Ying, S.-R. Zheng, Q.-G. Zhan, Z.-Y. Zhou, L. Chen, Y.-P.
Cai, Cryst. Eng. Comm. 12 (2010) 4012.
[21] A. Bhattacharyya, P.K. Bhaumik, A. Bauzá, P.P. Jana, A. Frontera, M.G.B. Drew, S.
Chattopadhyay, RSC Adv. 4 (2014) 58643.
[22] C. Biswas, S. Chattopadhyay, M.G.B. Drew, A. Ghosh, Polyhedron 26 (2007)
4411.
[23] P. Bhowmik, S. Jana, P.P. Jana, K. Harms, S. Chattopadhyay, Inorg. Chim. Acta 39
(2012) 53.
4. Summary
In the present work, we have synthesized four cadmium(II)
Schiff base complexes. N-substituted 1,2-diaminoethane has been
used to prepare four Schiff bases with four different aromatic
aldehydes. The denticity of the Schiff bases play important role
in dictating the structures of the complexes. Complex 1 features
a bis-ligand complex. Complex 2 is an example of end-to-end thio-
cyanate bridged dinuclear complex. Complex 3 contains trinuclear
cations with partial cubane [Cd3O4] core, in which cadmium(II)
[24] P.K. Bhaumik, S. Jana, S. Chattopadhyay, Inorg. Chim. Acta 390 (2012) 167.
[25] M. Das, S. Chattopadhyay, Transition Met. Chem. 38 (2013) 191.
[26] P.K. Bhaumik, K. Harms, S. Chattopadhyay, Polyhedron 68 (2014) 346.
[27] M. Das, S. Chattopadhyay, J. Mol. Struct. 1051 (2013) 250.
[28] M. Das, B.N. Ghosh, A. Valkonen, K. Rissanen, S. Chattopadhyay, Polyhedron 60
(2013) 68.
[29] S. Jana, P.K. Bhaumik, K. Harms, S. Chattopadhyay, Polyhedron 78 (2014) 94.
[30] H.-C. Fang, J.-Q. Zhu, L.-J. Zhou, H.-Y. Jia, S.-S. Li, X. Gong, S.-B. Li, Y.-P. Cai, P.K.
Thallapally, J. Liu, G.J. Exarhos, Cryst. Growth Des. 10 (2010) 3277.
[31] W.-K. Lo, W.-K. Wong, W.-Y. Wong, J. Guo, Eur. J. Inorg. Chem. (2005) 3950.
[32] J. Chakraborty, S. Thakurta, B. Samanta, A. Ray, G. Pilet, S.R. Batten, P. Jensen, S.
Mitra, Polyhedron 26 (2007) 5139.
centres are bridged by
l-1,1,1-OH. Complex 4 features a phe-
noxo-bridged dinuclear cadmium(II) complex. Variation in the
structures of the complexes is modulated by the change in the den-
ticity of the Schiff bases as well as the presence/absence of suitable
coordinated anions (NO3ꢁ, SCNꢁ, OHꢁ) or neutral coordinating
molecules (CH3OH) in the reaction medium. All four complexes
show fluorescence with fluorescence lifetime within 8–11 ns.
Acknowledgment
[33] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[34] G.M. Sheldrick, SADABS
: Software for Empirical Absorption Correction,
This work was supported by the DST, India, under FAST Track
Scheme (Order No. SR/FT/CS-118/2010, dated 15/02/2012).
Crystallographic data were collected at the DST-FIST, India-
funded Single Crystal Diffractometer Facility at the Department
of Chemistry, Jadavpur University.
University of Gottingen, Institute fur Anorganische Chemieder Universitat,
Gottingen, Germany, 1999–2003.
[35] Z.-L. You, H.-L. Zhu, Acta Crystallogr., Sect. C 61 (2005) m397.
[36] S. Sen, P. Talukder, S.K. Dey, S. Mitra, G. Rosair, D.L. Hughes, G.P.A. Yap, G. Pilet,
V. Gramlich, T. Matsushita, Dalton Trans. (2006) 1758.
[37] C.-H. Dai, F.-L. Mao, Synth. React. Inorg., Met.-Org., Nano-Met. Chem. 42 (2012)
537.
[38] S.-J. Peng, H.-Y. Hou, Q. Wang, T. Yang, C.-S. Zhou, Synth. React. Inorg., Met.-
Org., Nano-Met. Chem. 38 (2008) 746.
[39] K. Agapiou, M.L. Mejla, X. Yang, B.J. Holliday, Dalton Trans. (2009) 4154.
Appendix A. Supplementary material
´
[40] D. Cremer, J.A. Pople, J. Am. Chem. Soc. 97 (1975) 1354.
[41] S. Roy, P.K. Bhaumik, K. Harms, S. Chattopadhyay, Polyhedron 75 (2014) 57.
[42] S. Thakurta, R.J. Butcher, C.J. Gómez-García, E. Garribba, S. Mitra, Inorg. Chim.
Acta 363 (2010) 3981.
[43] M.A.S. Goher, L.A. Al-Shatti, F.A. Mautner, Polyhedron 16 (1997) 889.
[44] A. Sabtini, I. Bertini, Inorg. Chem. 4 (1965) 959.
[45] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, third ed., Wiley-Interscience, New York, 1978. p. 244.
[46] S. Shit, D. Saha, D. Saha, T.N.G. Row, C. Rizzoli, Inorg. Chim. Acta 415 (2014)
103.
[47] M.D. Lowther, W.F. Wacholtz, J.T. Mague, J. Chem. Crystallogr. 31 (2001) 395.
[48] P.K. Bhaumik, S. Roy, K. Harms, S. Chattopadhyay, Polyhedron 81 (2014) 168.
[49] R.A. Velapoldi, K.D. Mielenz, Standard Reference Materials: A Fluorescence
Standard Reference Material: Quinine Sulfate Dihydrate, National Bureau of
Standards Special Publication 260–64, National Bureau of Standards,
Washington, DC, 1980.
CCDC 1034469-1034472 contain the supplementary crystallo-
graphic data for complexes 1–4. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2015.04.018.
Reference
[1] L. Sacconi, I. Bertisi, R. Morassi, Inorg. Chem. 6 (1967) 1548.
[2] W.N. Wallis, S.C. Cummings, Inorg. Chem. 13 (1975) 991.
[3] M.G.B. Drew, C.V. Knox, S.M. Nelson, J. Chem. Soc., Dalton Trans. (1980) 942.
[4] J.P. Costes, Inorg. Chim. Acta 130 (1987) 17.
[5] P. Bhattacharya, J. Parr, A.T. Ross, A.M.Z. Slawin, J. Chem. Soc., Dalton Trans.
(1998) 3149.