Formation of three photoluminescent dinuclear cadmium(II) complexes with Cd2O2 cores

Article abstract of DOI:10.1016/j.poly.2015.01.025

Condensation of N,N-dimethyl-1,3-diaminpropane with salicylaldehyde, 3-methoxysalicylaldehyde and 3-ethoxysalicylaldehyde produces three Schiff bases, HL¹ [2-(3-(dimethylamino)propylimino)methyl)methoxyphenol], HL² [2-(3-(dimethylami

Full text of DOI:10.1016/j.poly.2015.01.025

Polyhedron 91 (2015) 10–17
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Formation of three photoluminescent dinuclear cadmium(II) complexes
with Cd2O2 cores
Sumit Roy a, Klaus Harms b, Shouvik Chattopadhyay a,
⇑
a Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
b Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35032 Marburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Condensation of N,N-dimethyl-1,3-diaminpropane with salicylaldehyde, 3-methoxysalicylaldehyde and
3-ethoxysalicylaldehyde produces three Schiff bases, HL1 [2-(3-(dimethylamino)propylimino)methyl)
methoxyphenol], HL2 [2-(3-(dimethylamino)propylimino)methyl)-6-methoxyphenol], and HL3 [2-(3-
(dimethylamino)propylimino)methyl)-6-ethoxyphenol], respectively. Addition of cadmium(II) chloride
to the methanol solution of the tridentate Schiff base, HL1, produces phenoxo-bridged dinuclear
cadmium(II) complex, [Cd2(L1)2(Cl)2] (1). Similarly, addition of cadmium(II) nitrate to the methanol solu-
tion of the tetradentate Schiff base, HL3, produces phenoxo-bridged dinuclear cadmium(II) complex,
[Cd2(L3)2(NO3)2] (3). On the other hand, [Cd(L2)2Cd(NCO)2] (2), is produced by the addition of
cadmium(II) perchlorate into the methanol solution of tetradentate Schiff base, HL2 followed by the addi-
tion of sodium cyanate. Structures of the complexes have been confirmed by single crystal X-ray diffrac-
tion studies. All complexes are dinuclear with Cd2O2 cores. Complex 1 contains square pyramidal
cadmium(II) centres, whereas complexes 2 and 3 contain octahedral cadmium(II) centres. All three com-
plexes show fluorescence.
Received 11 November 2014
Accepted 23 January 2015
Available online 3 February 2015
Keywords:
Cadmium(II)
Schiff base
Crystal structure
Supramolecular interaction
Photoluminescence
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
Schiff bases, prepared from the condensation of a diamine with
salicylaldehyde or its derivatives, which could easily form dinuclear
Potential uses of zinc and cadmium complexes [1–4] in the field
of electronic and opto-electronic research have attracted the atten-
tion of several groups to design and synthesize several Group 12
metal complexes [5–7]. The d10 electronic configuration of these
metal ions favours a variety of coordination geometries, which, in
turn, lead to the formation of diverse molecular architectures [5–
9]. Several dizinc(II) complexes have recently been synthesized as
structural mimics of the active sites of zinc(II) containing dinuclear
metallohydrolases (such as aminopeptidases, metallo-b-lactamases
and alkaline phosphatases), which catalyze the hydrolysis of
amides and esters of carboxylic and phosphoric acids [10–14]. On
the other hand, although cadmium(II) is uncommon in nature, it
is not biologically irrelevant and has often been shown to enhance
the activity in several zinc-containing metalloenzymes [15–17].
However, its potential as an analogue for Zn(II) in metalloenzymes
is relatively unexplored [18,19]. The common strategy to obtain
such model complexes is to use dinucleating ligands e.g. salen type
complexes exploiting the
atoms [20].
l2-bridging ability of phenoxo oxygen
The synthesis and characterization of new dinuclear
cadmium(II) complexes deserve further exploration following the
discovery of cadmium(II) containing enzyme, carbonic anhydrase
[21,22]. On the other hand, a significant number of supramolecular
cadmium(II) complexes has been synthesized in the last several
years with the aim to investigate their potential use in photonic
devices, sensors and catalysts and in host–guest chemistry [23–
27]. In the present work, we have used a tridentate N2O donor
and two tetradentate N2O2 donor Schiff bases to prepare three
dinuclear cadmium(II) complexes with Cd2O2 cores. Herein, we
would like to report the synthesis and characterization of three
phenoxo bridged dinuclear cadmium(II) complexes. All three com-
plexes exhibit fluorescence in DMSO medium.
2. Experimental
All starting materials and solvents were commercially available,
reagent grade, and used as purchased from Sigma–Aldrich without
further purification.
⇑
Corresponding author. Tel.: +91 33 2414 2941.
E-mail address: shouvik.chem@gmail.com (S. Chattopadhyay).
http://dx.doi.org/10.1016/j.poly.2015.01.025
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

S. Roy et al. / Polyhedron 91 (2015) 10–17
11
Caution!!!
2.1.3. Synthesis of [Cd2(L3)2(NO3)2] (3)
The 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.
A methanolsolution of3-ethoxysalicylaldehyde (1 mmol, 0.166 g)
and N,N-dimethyl-1,3-diaminopropane (1 mmol, 0.125 mL) was
refluxed for 1 h to prepare a tetradentate N2O2 donor Schiff base, 2-
(3-(dimethylamino)propylimino)methyl)-6-ethoxyphenol (HL3). The
Schiff base was used directly for the preparation of complex 3. A
methanol solution cadmium(II) nitrate tetrahydrate (1 mmol,
0.308 g) was added drop wise to the methanol solution of Schiff base
with constant stirring for 20 min. Diffraction quality single crystals
were obtained after few days on slow evaporation of the solution in
open atmosphere.
2.1. Preparations
2.1.1. Synthesis of [Cd2(L1)2(Cl)2] (1)
A methanol solution of salicylaldehyde (1 mmol, 0.104 mL) and
N,N-dimethyl-1,3-diaminopropane (1 mmol, 0.103 mL) and was
refluxed for 1 h to prepare a tridentate N2O donor Schiff base, 2-
(3-(dimethylamino)propylimino)methyl)methoxyphenol (HL1). The
Schiff base was used directly for the preparation of complex 1. A
methanol-DMSO solution of cadmium(II) chloride dihydrate
(1 mmol, 0.219 g) was added drop-wise to the methanol solution
of Schiff base with constant stirring. The stirring was continued for
30 min. Single crystals, suitable for X-ray diffraction, were
obtained after few days on slow evaporation of the solution in open
atmosphere.
Yield: 0.57 g (68%). Anal. Calc. for C28H42Cd2N6O10 (FW 847.50):
C, 39.68; H, 5.00; N, 9.92%. Found: C, 39.63; H, 4.94; N, 9.97%. IR
(KBr, cmꢀ1):1631 (
mC@N), 1384 (mNO3); UV–Vis, kmax (nm), (emax
(L molꢀ1 cmꢀ1)) (DMSO), 255 (3.4 ꢁ 104), 334 (6 ꢁ 103).
2.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a Perkin–Elmer 240C elemental analyzer. Infrared spec-
tra in KBr (4500–500 cmꢀ1) were recorded using a PerkinElmer
FT-IR spectrum two spectrometer. 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 spectra were recorded
in a 2h range of 5–50° using a 1D Lynxeye detector under ambient
conditions.
Yield: 0.51 g (73%). Anal. Calc. for C24H34Cd2Cl2N4O2 (FW
706.25): C, 40.81; H, 4.85; N, 7.93. Found: C, 40.72; H, 4.78; N,
7.99%. IR (KBr, cmꢀ1):1626 (
mC@N); UV–Vis, kmax (nm), (emax
(L molꢀ1 cmꢀ1)) (DMSO), 261 (1.1 ꢁ 104), 317 (6 ꢁ 103).
2.1.2. Synthesis of [Cd(L2)2Cd(NCO)2] (2)
A
methanol solution of 3-methoxysalicylaldehyde (1 mmol,
0.152 g) and N,N-dimethyl-1,3-diaminopropane (1 mmol, 0.125 mL)
was refluxed for 1 h to prepare a tetradentate N2O2 donor Schiff base,
2-(3-(dimethylamino)propylimino)methyl)-6-methoxyphenol (HL2).
The Schiff base was used directly for the preparation of complex 2. A
methanol solution of cadmium(II) perchlorate hexahydrate (1 mmol,
0.419 g) was added to the methanol solution of Schiff base and
refluxed for 1 h. A methanol solution of sodium cyanate (1 mmol,
0.065 g) was then added to it and refluxed further for ca. 1 h.
Diffraction quality single crystals were obtained after few days on
slow evaporation of the solution in open atmosphere.
2.3. X-ray crystallography
Single crystals of complex 1 was used for data collection using a
Bruker D8 QUEST area detector diffractometer equipped with gra-
phite-monochromated Mo-Ka radiation (k = 0.71073 Å) at 100 K.
The X-ray intensity data were measured. The frames were integrat-
ed with the Bruker SAINT Software package using a wide-frame
algorithm. On the other hand, single crystals of complexes 2 and
3, having suitable dimensions, were used for data collection using
a Bruker SMART APEX II diffractometer. The molecular structure
was solved by direct method and refined by full-matrix least
squares on F2 using SHELXL-2014/7 [28]. Non hydrogen atoms were
refined anisotropically. All hydrogen atoms were placed in their
geometrically idealised positions and constrained to ride on their
parent atoms. Numerical and/or multi-scan absorption corrections
were applied to the data using the program SADABS [29]. The crystal-
lographic and refinement data of three complexes are summarized
in Table 1.
Yield: 0.57 g (74%). Anal. Calc. for C28H38Cd2N6O6 (FW 779.46):
C, 43.50; H, 4.91; N, 10.78. Found: C, 43.45; H, 4.87; N, 10.85%. IR
(KBr, cmꢀ1):1626 (
mC@N), 2191, 2171 (mNCO); UV–Vis, kmax (nm),
(
emax (L molꢀ1 cmꢀ1)) (DMSO), 262 (1.8 ꢁ 104), 333 (3.7 ꢁ 103).
Table 1
Crystal data and refinement details of complexes 1, 2 and 3.
1
2
3
Formula
C24H34Cd2Cl2N4O2 C28H38Cd2N6O6 C28H42Cd2N6O10
Formula weight
Temperature (K)
706.25
100
779.46
150
847.50
150
3. Results and discussions
Crystal system
Space group
orthorhombic
Pbca
orthorhombic monoclinic
Pbca
I2/a
a (Å)
b (Å)
c (Å)
b
7.7788(4)
19.7647(8)
35.0727(16)
90
17.6623(5)
17.5950(5)
20.0647(5)
90
16.2666(13)
11.1104(6)
18.889(2)
93.503(8)
4
1.652
1.309
1712
22505
3050
3.1. Synthesis
One tridentate Schiff base ligand, HL1, and two tetradentate
Schiff base ligands, HL2 and HL3, were synthesized by the conden-
sation of N,N-dimethyl-1,3-diaminopropane with salicylaldehyde,
3-methoxysalicylaldehyde and 3-ethoxysalicylaldehyde, respec-
tively, following the literature method [30–35].
Z
8
8
Dcalc (g cmꢀ3
)
1.740
1.804
2816
24229
4881
1.661
1.414
3136
88820
5986
4116
379
0.044
l
(mmꢀ1
F(000)
)
Total reflections
The methanol solution of HL1 was made to react with methanol-
DMSO solution of cadmium(II) chloride dihydrate in stirring condi-
tion to prepare complex 1, in which each cadmium(II) centre
assumes a square pyramidal geometry. Complex 2 was produced
by addition of methanol solution of cadmium(II) perchlorate hex-
ahydrate followed by the addition of sodium cyanate under
Unique reflections
Observed data [I > 2
No. of parameters
r
(I)] 4566
2523
216
0.036
311
0.025
0.0392, 0.0866
0.0360, 0.0854
(Rint
R1, wR2 (all data)
R1, wR2 [I > 2 (I)]
)
0.0477, 0.0908 0.0497, 0.1232
0.0260, 0.0686 0.0406, 0.1159
r

12
S. Roy et al. / Polyhedron 91 (2015) 10–17
refluxing condition. On the other hand, Complex 3 was produced
a tridentate deprotonated Schiff base, (L1)ꢀ and one terminal
chloride, {Cl(1A)/Cl(1B}. The fifth coordination site of each
cadmium(II) centre is occupied by another phenoxo oxygen atom,
{O(8B)/O(8A)}, from a second (L1)ꢀ ligand. Thus, the two phenoxo
oxygen atoms, O(8A) and O(8B), bridge two cadmium(II) centres
and link the two halves of the dinuclear complex about a pseudo-
2-fold symmetry axis which lies normal to the Cd2O2 ring. The
Cd–O and Cd–N distances fall within the range 2.213(2)–
2.288(3) Å and 2.286(4)–2.369(5) Å respectively, as were also
observed in other reported complexes [42]. The Cd(1)–O(8)–Cd(1)
bridging angles are 104.2(1)° and 105.3(1)°. The geometry of a pen-
ta-coordinated metal complex may be confirmed by the Addison
on stirring HL3 with cadmium(II) nitrate tetrahydrate. In both
,
complexes 2 and 3, the cadmium(II) centres assume octahedral
geometries. Formation of complexes is shown in Scheme 1.
It is to be noted here that both cadmium(II) centres are in simi-
lar N2O2Cl environment in complex 1, whereas cadmium(II) cen-
tres are in different environment both in complexes 2 and 3.
Literature also shows that that all structurally characterized
cadmium(II) complexes with N-substituted propane-1,3-diamine
based tridentate N2O donor Schiff bases have similar dinuclear
skeletons with equivalent cadmium(II) centres [36–38]. On the
other hand, N-substituted propane-1,3-diamine based tetradentate
N2O2 donor Schiff bases form dinuclear cadmium(II) complexes
with two octahedral cadmium(II) centres residing in non-identical
ligand environment [20,39–41]. All such complexes are gathered in
Scheme 2 and 3.
parameter (s) that is ideally zero for a square-pyramid and is one
for a trigonal bipyramid. In the present complex, the geometry
around Cd(1A) centre is very close to ideal square pyramidal with
trigonality indices
centre has a distorted square pyramidal geometry with
= ( and b are the two largest Ligand–Metal–
s
(Addison parameter) = 0.016, whereas Cd(1B)
s
= 0.355,
{s
a
ꢀ b)/60, where
a
3.2. Description of structures
Ligand angles of the coordination sphere} [43]. The distance
between the two cadmium(II) centres is 3.5775(9) Å. Selected bond
distances and bond angles are gathered in Tables 2 and 3, respec-
tively. The six member chelate rings, {Cd(1)–N(1)–C(2)–C(3)–
C(4)–N(5)} assume twist-boat and envelope conformations, with
3.2.1. [Cd2(L1)2(Cl)2] (1)
Complex 1 crystallizes in orthorhombic space group, Pbca. The
complex features a double phenoxo bridged dinuclear cadmium(II)
complex, in which both cadmium(II) are penta-coordinated
(Fig. 1). Each cadmium(II) centre {Cd(1A)/Cd(1B)} is bonded to one
imine nitrogen atom,{N(5A)/N(5B)}, one amine nitrogen atom,
{N(1A)/N(1B)} and one phenoxo oxygen atom, {O(8A)/O(8B)}, from
puckering parameters, q = 0.581(6) Å, h = 17.0(5)°,
and q = 0.872(4) Å, h = 92.9(3)°, = 335.4(3)° respectively [45].
The deviations of two Cd(1) from the least squares plane passing
u = 178.3(19)°,
u
Scheme 1. Preparation of complexes 1, 2 and 3.

S. Roy et al. / Polyhedron 91 (2015) 10–17
13
Scheme 2. Schematic representation of dinuclear cadmium(II) complexes with N-substituted propane-1,3-diamine based tridentate N2O donor Schiff bases, reported in
literature.
Scheme 3. Schematic representation of dinuclear cadmium(II) complexes with N-substituted propane-1,3-diamine based tetradentate N2O2 donor Schiff bases, reported in
literature.
through O(8), O(8), N(1), N(5) are 0.7764(3), 0.7964(5) Å respective-
ly. There are no significant supramolecular interactions in the
complex.
0.0130(4) and ꢀ0.013(3) Å, respectively. The rhombohedral angles
are O(3)–Cd(1)–O(1), 76.02(9)°, Cd(1)–O(1)–Cd(2), 104.2(1)°,
O(1)–Cd(2)–O(3) 75.50(9)°, Cd(2)–O(3)–Cd(1), 104.3(1)°. The
Cdꢂ ꢂ ꢂCd distance within the dinuclear unit is 3.5780(5) Å. The Cd–
Ophenoxo bond distances are in the range 2.257(3)–2.275(3) Å and
the Cd–Omethoxy distances fall in the range 2.549(3)–2.552(3) Å.
Therefore, it could be concluded that Cd–Omethoxy distances are
larger than Cd–Ophenoxo distances, as were observed in similar com-
plexes [20]. On the other hand, Cd–Nimine distances {2.268(3)–
2.286(3) Å} are shorter than the Cd–Namine {2.443(3)–2.449(3) Å}
distances, as were also observed in similar systems [44].
3.2.2. [Cd(L2)2Cd(NCO)2] (2)
Complex 2 crystallizes in the orthorhombic space group Pbca. A
perspective view of complex with selected atom-numbering scheme
is shown in Fig. 2. The selected bond distances and bond angles are
gathered in Tables 4 and 5, respectively. In the complex, both
cadmium(II) centres possess crystallographic two fold rotational
axes. Within the dinuclear unit, two octahedral cadmium(II) centres
are bridged by two phenoxo oxygen atoms. The Cd(1) centre is sur-
rounded by two phenoxo oxygen atoms, O(1) and O(3), two imine
nitrogen atoms, N(2) and N(4), and two amine nitrogen atoms,
N(1) and N(3), from two deprotonated Schiff base ligands, (L2)ꢀ, in
fac orientations. The Cd(2) centre is coordinated by two phenoxo
oxygen atoms, O(1) and O(3), and two methoxy oxygen atoms,
O(2) and O(4), from two deprotonated Schiff base ligands, and two
nitrogen atoms, N(5) and N(6), from two terminal cyanate. The
dinuclear bridging unit Cd2O2 describes a rhombohedral plane.
Deviations of the coordinating atoms Cd(1), O(1), Cd(2) and O(3)
from the least-square Cd2O2 plane are 0.0131(4), ꢀ0.013(3),
The conformations of the saturated six membered chelate rings
Cd(1)–N(1)–C(3)–C(4)–C(5)–N(2) and Cd(1)–N(3)–C(16)–C(17)–
C(18)–N(4) are intermediate between chair and half-chair, with
puckering parameters q = 0.762(4) Å, h = 163.7(3)°,
u = 164.3(11)°
and q = 0.781(3) Å, h = 158.5(3)°, = 168.9(9)°, respectively [45].
u
There are no significant supramolecular interactions in the
complex.
3.2.3. [Cd2(L3)2(NO3)2] (3)
Complex 3 crystallizes in monoclinic space group I2/a. A per-
spective view of complex with selective atom-numbering scheme

14
S. Roy et al. / Polyhedron 91 (2015) 10–17
Fig. 2. Perspective view of complex 2 with selective atom-numbering scheme.
Hydrogen atoms are not shown for clarity.
Table 4
Selected bond lengths (Å) of complexes 2 and 3.
2
3
Cd(1)–O(1)
Cd(1)–N(1)
Cd(1)–O(3)
Cd(1)–N(2)
Cd(1)–N(3)
Cd(1)–N(4)
Cd(2)–O(1)
Cd(2)–O(2)
Cd(2)–O(3)
Cd(2)–O(4)
Cd(2)–O(4B)
Cd(2)–N(5)
Cd(2)–N(6)
2.263(3)
2.444(3)
2.257(3)
2.286(3)
2.450(3)
2.268(3)
2.272(3)
2.549(3)
2.275(3)
2.552(3)
–
2.247(3)
2.486(5)
–
2.254(4)
–
–
2.250(3)
2.575(4)
2.450(6)
–
2.08(2)
–
–
Fig. 1. Perspective view of complex 1 with selective atom-numbering scheme.
Hydrogen atoms are not shown for clarity.
Table 2
Selected bond lengths (Å) in complex 1.
x = A, y = B
x = B, y = A
Cd(1x)–Cl(1x)
Cd(1x)–O(8x)
Cd(1x)–N(1x)
Cd(1x)–N(5x)
Cd(1x)–O(8y)
2.4288(13)
2.264(3)
2.369(5)
2.286(4)
2.288(3)
2.4356(12)
2.213(3)
2.334(4)
2.320(4)
2.271(3)
2.180(4)
2.156(4)
Table 3
Table 5
Selected bond angles (°) of complex 2.
Selected bond angles (°) of complex 1.
x = A, y = B
x = B, y = A
O(1)–Cd(1)–N(1)
100.58(10)
O(1)–Cd(2)–O(2)
65.30(9)
Cl(1x)–Cd(1x)–O(8y)
Cl(1x)–Cd(1x)–O(8x)
Cl(1x)–Cd(1x)–N(1x)
Cl(1x)–Cd(1x)–N(5x)
O(8y)–Cd(1x)–O(8x)
O(8y)–Cd(1x)–N(1x)
O(8y)–Cd(1x)–N(5x)
O(8x)–Cd(1x)–N(1x)
O(8x)–Cd(1x)–N(5x)
N(1x)–Cd(1x)–N(5x)
109.38(8)
118.26(9)
102.91(10)
111.91(10)
72.09(11)
90.42(13)
137.50(13)
138.50(13)
79.95(13)
89.90(14)
108.48(8)
124.64(9)
107.96(10)
100.56(10)
73.36(11)
92.83(12)
148.82(12)
127.38(13)
81.03(13)
88.74(14)
O(1)–Cd(1)–O(3)
O(1)–Cd(1)–N(2)
O(1)–Cd(1)–N(3)
O(1)–Cd(1)–N(4)
O(3)–Cd(1)–N(1)
O(3)–Cd(1)–N(2)
O(3)–Cd(1)–N(3)
O(3)–Cd(1)–N(4)
N(1)–Cd(1)–N(2)
N(1) –Cd(1) –N(3)
N(1)–Cd(1)–N(4)
N(2)–Cd(1)–N(3)
N(2)–Cd(1)–N(4)
N(3)–Cd(1)–N(4)
76.02(9)
81.14(10)
93.74(10)
154.72(10)
92.74(10)
153.51(10)
100.79(10)
82.03(10)
78.34(11)
162.32(11)
92.78(11)
93.84(11)
122.88(11)
78.07(11)
O(1)–Cd(2)–O(3)
O(1)–Cd(2)–O(4)
N(5)–Cd(2)–N(6)
O(1)–Cd(2)–N(5)
O(1)–Cd(2)–N(6)
O(2)–Cd(2)–O(3)
O(2)–Cd(2)–O(4)
O(2)–Cd(2)–N(5)
O(2)–Cd(2)–N(6)
O(3)–Cd(2)–O(4)
O(3)–Cd(2)–N(5)
O(3)–Cd(2)–N(6)
O(4)–Cd(2)–N(5)
O(4)–Cd(2)–N(6)
75.50(9)
139.35(9)
121.99(17)
105.81(12)
119.35(15)
139.08(9)
155.29(9)
86.23(11)
81.91(15)
65.07(9)
116.47(11)
108.92(16)
84.21(11)
83.95(15)
is shown in Fig. 3. The selected bond distances and angles are pre-
sented in Tables 4 and 6, respectively. Within the dinuclear unit,
cadmium(II) centres, Cd(1) and Cd(2), are bridged by two phenoxo
oxygen atoms, O(1) and O(1)a respectively. The Cd(1) centre is in
distorted octahedral environment, coordinated by two amine
nitrogen atoms, N(1) and N(1)a, two imine nitrogen atoms, N(2)
and N(2)a, and two phenoxo oxygen atoms, O(1) and O(1)a, from
two deprotonated Schiff base ligands, (L3)ꢀ, in fac orientations.
On the other hand, Cd(2) centre is coordinated by two phenoxo
oxygen atoms, O(1) and O(1)a, and two ethoxy oxygen atoms,
O(2) and O(2)a, from two deprotonated Schiff base ligands, (L3)ꢀ.
The remaining coordination sites of Cd(2) are occupied by four
oxygen atoms, O(3), O(4B) and O(3)a, O(4B)a, from two chelating
nitrate ligands respectively, The small value {29.2°(5)} of the

S. Roy et al. / Polyhedron 91 (2015) 10–17
15
angles, {O(3)–Cd(2)–O(4B)} and {O(3)a–Cd(2)–O(4B)a}, subtended
Table 6
Selected bond angles (°) of complex 3.
by the two O atoms at the metal, traces on the point that the
two oxygen atoms are sharing one axial site, i.e. the nitrate group
is better thought of as a single entity occupying just one stereoche-
mical site in the coordination sphere of the metal instead of as a
bidentate ligand. Thus the geometry around the Cd(2) centre is dis-
torted octahedral.
For Cd(2), the average bond distances of Cd–Oethoxy, are larger
than that of Cd–Ophenoxo distances. On the other hand, Cd–Nimine
distances {2.253(4) Å} are shorter than the Cd–Namine {2.486(5) Å}
distances, as were also observed in similar systems [44]. The bond
lengths are less constant in any structure and for any coordination
number.
The dinuclear bridging unit Cd2O2 describes a rhombohedral
plane. The rhombohedral angles are O(1)–Cd(1)–O(1)a, 75.6(1)°;
Cd(1)–O(1)a–Cd(2), 104.5(1)°; O(1)a–Cd(2)–O(1) 75.5(1)°; Cd(2)–
O(1)–Cd(1) 104.5(1)°. The Cdꢂ ꢂ ꢂCd distance within the dinuclear
unit is 3.5547(7) Å. The conformations of the saturated six mem-
bered chelate rings Cd(1)–N(1)–C(3)–C(4)a–C(5)a–N(2)a and
Cd(1)–N(2)–C(5)–C(4)–C(3)a–N(1)a are intermediate between chair
and half-chair, with puckering parameters q = 0.771(6) Å, h =
O(1)–Cd(1)–N(1)
100.34(15)
O(1)–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
O(1)–Cd(1)–N(1)a
N(1)–Cd(1)–N(2)a
N(2)–Cd(1)–N(2)a
N(1)–Cd(1)–N(1)a
O(1)–Cd(1)–N(2)a
O(1)–Cd(1)–O(1)a
O(3)–Cd(2)–O(3)a
O(3)a–Cd(2)–O(4B)
O(4B)–Cd(2)–O(4B)a
O(1)–Cd(2)–O(2)
O(1)–Cd(2)–O(3)
O(2)–Cd(2)–O(3)
O(1)–Cd(2)–O(4B)
O(2)–Cd(2)–O(4B)
O(3)–Cd(2)–O(4B)
O(2)–Cd(2)–O(2)a
O(1)–Cd(2)–O(2)a
O(1)–Cd(2)–O(4B)a
O(2)–Cd(2)–O(3)a
O(2)–Cd(2)–O(4B)a
O(1)–Cd(2)–O(3)a
153.74(14)
94.73(17)
92.76(15)
77.19(16)
122.20(16)
163.44(18)
82.35(14)
75.61(11)
168.5(2)
140.5(6)
119.8(8)
65.28(11)
92.21(17)
97.43(17)
101.9(6)
76.9(4)
29.2(5)
155.83(11)
138.53(11)
125.9(5)
80.13(17)
91.0(5)
164.2(5)°,
u = 168.2(19)° and q = 0.771(6) Å, h = 15.8(5)°, u = 11.8(19)°
96.90(17)
respectively, [45]. (Symmetry transformation a = 1/2 ꢀ x,y,1 ꢀ z).
Symmetry transformation, a = 1/2 ꢀ x,y,1 ꢀ z.
The complex shows only one significant C–Hꢂ ꢂ ꢂ
p interaction.
The hydrogen atom, H(1C), attached to C(1), is involved in C–
Hꢂ ꢂ ꢂ interaction with the -electron cloud of a symmetry related
(1 ꢀ x,2 ꢀ y,1 ꢀ z) phenyl ring, C(7)–C(8)–C(9)–C(10)–C(11)–C(12)
interaction forms
p
p
of neighbouring molecule. The C–Hꢂ ꢂ ꢂ
p
a
1633 cmꢀ1. The bifurcated bands at 2191 and 2171 cmꢀ1 in the
IR spectrum of complex 2 indicate the presence of terminal cyanate
groups in slightly different environments. The bands in the range
of 2998–2835 cmꢀ1 due to alkyl C–H bond stretching vibrations
are customarily noticed in the IR spectra of all three complexes.
IR spectra of the complexes 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 due to the reduction of double bond characters
of the C@N bonds, caused by the coordination of nitrogen atoms
to the cadmium(II) centres and are in agreement with results
obtained from other similar complexes described previously [7].
Electronic spectra of complexes and ligands are recorded in
DMSO medium in the range 200–800 nm. Absorption spectra of
ligands exhibit four bands, of which first two bands around 225
supramolecular one-dimensional chain as shown in Fig. 4. There
are no other significant supra-molecular interactions in the
complex.
3.3. IR, electronic and fluorescence spectra
In IR spectra of all complexes, distinct bands due to azomethine
(C@N) stretching vibrations appear in the range of 1626–
and 260 nm may be attributed to
p–
p⁄ transitions and the two
bands at around 325 and 420 nm [46]. Although same trends are
observed in the complexes, complexation leads to slight shifts in
the positions of these bands. There is no bands corresponding to
d–d electronic transitions as expected for cadmium(II) complexes
with d10 electronic configurations [20].
All Complexes exhibit luminescence in DMSO medium. On
exciting at 317, 333 and 334 nm, emissions are observed at 418,
421, and 419 nm for complexes 1, 2, and 3 respectively. Emission
of complexes is tentatively attributed to the intra-ligand transi-
tions modified by metal coordination. The fluorescence lifetimes
of complexes are investigated in DMSO solution at room tem-
perature. Lifetimes of 1, 2 and 3 are about 12.66, 12.50, and
12.46 ns (Table 7) respectively, which are similar to other
cadmium(II) complexes [36]. Decay profiles (Fig. 5) were fitted to
a multi-exponential model:
X
IðtÞ ¼
aiexpðꢀt=siÞ
i
where, mono-exponential functions are used to fit the emission of
three complexes with and obtaining v2 close to 1.
Relative fluorescence quantum yields for all complexes were
measured in DMSO using quinine sulfate (in 0.5 (M) H2SO4,
Fig. 3. Perspective view of complex 3 with selective atom-numbering scheme. Only
the major fraction (O4B) of the disordered oxygen (O4) is shown. Hydrogen atoms
are not shown for clarity. Symmetry transformation, a = 1/2 ꢀ x,y,1 ꢀ z.

16
S. Roy et al. / Polyhedron 91 (2015) 10–17
Fig. 4. One-dimensional supramolecular chain in complex 3, generated through C–Hꢂ ꢂ ꢂ
p interactions. Selected hydrogen atoms are omitted for clarity.
information). The simulated patterns were calculated from the sin-
gle crystal structural data (cif file) using CCDC Mercury software.
Table 7
The details data of photoluminescence and time-resolved photoluminescence decays
of complexes 1, 2 and 3.
4. Summary
Complex
kex (nm)
kem (nm)
A1 (%)
s
(ns)
v2
1
2
3
317
333
334
418
421
419
100
100
100
12.66
12.50
12.46
1.033545
1.074073
1.065595
In the present work, we have synthesized three dinuclear
cadmium(II) Schiff base complexes containing Cd2O2 cores. N-sub-
stituted 1,3-diaminopropane has been used to prepare three Schiff
bases with three different aromatic aldehydes. Versatile coordinat-
ing ability of different anions with varying binding strength along
with the variation in denticity of the Schiff bases may play impor-
tant role in dictating the structures of the complexes. All three com-
plexes show fluorescence with lifetimes ꢃ12 ns. Keeping in mind
the novel role of cadmium(II) complexes in the field of electronic
and opto-electronic research, the present findings provide insight
and serve as a prototype for preparing other such complexes.
Acknowledgement
This work was supported by the DST, India, under FAST Track
Scheme (Order No. SR/FT/CS-118/2010, dated 15/02/2012).
Appendix A. Supplementary data
CCDC 1033556, 1033220 and 1033221 contain the supplemen-
tary crystallographic data for 1, 2 and 3 respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Fig. 5. Lifetime decay profile of complexes 1, 2 and 3.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2015.01.025.
U
= 0.54) as the quantum yield standard [47]. The fluorescence
quantum yields of complexes 1, 2, and 3 are 0.00511, 0.00401,
0.03219 respectively. If Ux and Us are the quantum yields of a
given fluorophore species ‘x’ and the standard ‘s’, respectively, then
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