Exploration of photocatalytic activity of an end-on azide bridged one-dimensional cadmium(II) Schiff base complex for the degradation of organic dye in visible light

Article abstract of DOI:10.1016/j.poly.2016.09.018

A one-dimensional polynuclear end-on azide bridged octahedral cadmium(II) Schiff base complex, [{CdL(μ-1,1-N₃)}₂Cd(μ-1,1-N₃)₂·1.76CH₃OH]_n{HL?=?2-(3-(dimethylamino)propyliminomethyl)-6-ethox

Full text of DOI:10.1016/j.poly.2016.09.018

Accepted Manuscript
Exploration of photocatalytic activity of an end-on azide bridged one-dimen-
sional cadmium(II) Schiff base complex for the degradation of organic dye in
visible light
Sumit Roy, Klaus Harms, Antonio Bauzá, Antonio Frontera, Shouvik
Chattopadhyay
PII:
S0277-5387(16)30446-6
DOI:
http://dx.doi.org/10.1016/j.poly.2016.09.018
POLY 12206
Reference:
Polyhedron
To appear in:
Please cite this article as: S. Roy, K. Harms, A. Bauzá, A. Frontera, S. Chattopadhyay, Exploration of photocatalytic
activity of an end-on azide bridged one-dimensional cadmium(II) Schiff base complex for the degradation of organic
dye in visible light, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.09.018
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Exploration of photocatalytic activity of an end-on azide bridged
one-dimensional cadmium(II) Schiff base complex for the
degradation of organic dye in visible light
Sumit Roya, Klaus Harmsb, Antonio Bauzác, Antonio Fronterac,*, Shouvik
Chattopadhyaya,*
a Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata – 700 032, India.
bFachbereichChemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35032 Marburg,
Germany.
cDepartament de Química, Universitat de les IllesBalears, Crta de Valldemossa km 7.5, 07122
Palma de Mallorca (Baleares), SPAIN. e-mail: toni.frontera@uib.es
* Corresponding authors. Tel.: +91 33 2457 2941 (S. Chattopadhyay).
E-mail addresses: toni.frontera@uib.es (A. Frontera), Shouvik.chem@gmail.com
(S. Chattopadhyay).
Abstract: A one-dimensional polynuclear end-on azide bridged octahedral cadmium(II) Schiff
base
complex,
[{CdL(µ-1,1-N3)}2Cd(µ-1,1-N3)2·1.76CH3OH]n
{HL
=
2-(3-
(dimethylamino)propyliminomethyl)-6-ethoxyphenol} has been synthesized and characterized
by X-ray crystallography. The complex crystallizes in monoclinic space group C2/c with cell
dimensions, a = 21.4706(8) Å, b = 9.9542(4) Å, c = 19.3257(7) Å, β = 103.7819(11)°. Extended
supra-molecular assemblies were generated through weak non-covalent interactions. The
energetic features of these interactions have also been studied by means of DFT calculations.
1

The complex exhibits good photoluminescence in DMSO medium. The application of the
complex as a photocatalyst for the decomposition of organic dye in visible light has been
explored.
Keywords: Cadmium(II); Schiff base; End-on Azide; Crystal structure; Photocatalyst; DFT
study.
1. Introduction
Cadmium was thought to be a toxic element for long. It is a very challenging task till date
to develop appropriate chelating ligands for the treatment of cadmium intoxication [1,2].
However, following the discovery of cadmium(II) containing enzyme, carbonic anhydrase [3,4],
this group 12 metal is currently not considered as biologically untouchable. On the other hand, as
a result of the d10 configuration of cadmium(II) with no CFSE in any geometry, cadmium(II)
complexes may adopt varieties of structures thereby attracting the attention of the ‘crystal
engineers’ [5,6]. They are also known to have interesting photochemical and photophysical
properties with potential applications as light-emitting diodes, luminescent probes and
photovoltaic devices [7-10]. Supramolecular systems based on cadmium(II) complexes have also
received much attention because of their potential use in material science [11-13]. A new
emerging application of cadmium(II) complexes as photocatalytic for the degradation of organic
dyes in UV light was established in recent years [14,15]. The environmental contamination
caused by several organic dyes, e.g. methylene blue (MB) [which is widely used in the textile,
printing and paper industries], has caused serious pollution with increasing industrialization and
population and the synthesis and characterization of new photocatalysts is a hot research topic
for their applications in the purification of water and air by thoroughly decomposing those
2

organic compounds [16-18]. It is to be noted here that there is no report of the application of
cadmium(II) Schiff base complexes in photocatalysis using visible light.
In the present work, a tetradentate N2O2 donor salicylaldimine Schiff base has been used
to prepare an end-on azide bridged polynuclear cadmium(II) complex. The X-ray crysytal
structure determination confirms that the complex contains a trinuclear building block with
{Cd(µ-1,1-N3)}2Cd core. The complex has been shown to have good photocatalytic activity to
decompose methylene blue in visible light. Herein, we would like to report the synthesis
characterization, self assembly and photocatalytic activity of a polynuclear end-on azide bridged
cadmium(II) complex with a salicylaldimine Schiff base.
2. Experimental
2.1. Preparations
Methylene Blue was purchased from Loba chemie and used without further purification.
All other starting materials and solvents were commercially available, reagent grade, and used as
purchased from Sigma-Aldrich without further purification.
2.1.1. Synthesis of [{CdL(µ-1,1-N3)}2Cd(µ-1,1-N3)2·1.76CH3OH]n
A methanol solution of 3-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)propyliminomethyl)-6-ethoxyphenol (HL). A methanol
solution of cadmium(II) acetate dihydrate (1 mmol, 0.266 g) was added drop wise to the
methanol solution of Schiff base followed by addition of aqueous methanol solution of sodium
azide (1 mmol, 0.065 g) with constant stirring. The stirring was continued for additional 30 min.
3

Block shaped yellow coloured crystals, suitable for X-ray diffraction, were obtained after few
days on slow evaporation of the solution in open atmosphere.
Yield: 0.76 g (72%). Anal. Calc. for C29.76H49.04Cd3N16O5.76, (FW 1060.26): C, 33.71; H,
4.76; N, 21.13; Found: C, 33.65; H, 4.71; N, 21.19 %. IR (KBr, cm-1): 1636 (υC=N), 2072, 2038
(υN3), 3518-3374 (υOH), 2993-2842 (υCH). UV-Vis, λmax (nm), [εmax (L mol-1 cm-1)] (DMSO), 266
(2.1 × 104), 332 (5.8 × 103), 421 (1.1 × 103).
2.2. Physical measurements
Elemental analysis (carbon, hydrogen and nitrogen) was performed on a Perkin-Elmer
240C elemental analyzer. Infrared spectrum in KBr (4000-400 cm-1) was recorded using a
PerkinElmer Spectrum Two FTIR spectrophotometer. Electronic spectrum in DMSO (800-200
nm) was recorded on a PerkinElmer Lambda 35 UV-Vis spectrophotometer. Fluorescence
spectrum in DMSO was obtained on a Hitachi F-7000 Fluorescence spectrophotometer at room
temperature. Lifetime measurement was recorded using Hamamatsu MCP photomultiplier
(R3809) and was analyzed by using IBHDAS6 software.
2.3. X-ray crystallography
Single crystal of complex having suitable dimension, was used for data collection using a
Bruker SMART APEX II diffractometer equipped with graphite-monochromated Mo-Kα
radiation (λ = 0.71073 Å) at 100 K. The molecular structure was solved by direct method and
refined by full-matrix least squares on F2 using SHELXL-2014/7 [19]. X-ray intensity data were
measured. The frames were integrated with the Bruker SAINT Software package using a wide-
frame algorithm. Non hydrogen atoms were refined anisotropically. Hydrogen atoms attached to
oxygen were located by difference Fourier maps and were kept at fixed positions. Others
4

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 [20]. The crystallographic and refinement data of complex are
summarized in Table 1.
2.4. Photocatalytic Measurement
A photocatalytic experiment in aqueous solution was carried out in a typical process [14].
A 36 W Hg vapour lamp was used as the visible light source, and the catalytic degradation was
carried out with 100 mL of Methylene Blue solution (10 mg L-1) with the complex using as
catalyst. The mixture was stirred for 10 min in a dark environment to get a balance between
adsorption and desorption. Then, the solution was stirred constantly. A 4 mL sample was taken
from the reaction system in an interval of 10 min and the supernatant liquid obtained by
centrifugation was used for collecting the UV-Visible spectrum. The characteristic peak for
methylene blue at λ = 607 nm was employed to monitor the photocatalytic degradation.
2.5. Theoretical methods
The calculations of non-covalent interactions were carried out using the TURBOMOLE
version 7.0 [21], using the BP86-D3/def2-TZVP level of theory. To evaluate the interactions in
the solid state, we have used the crystallographic coordinates. This procedure and level of theory
have been successfully used to evaluate similar interactions [22-25]. Interaction energies were
computed by calculating the difference between the energies of isolated monomers and their
assembly. The interaction energies were corrected for the Basis Set Superposition Error (BSSE)
using the counterpoise method [26]. The NCI plot is a visualization index based on the electron
density and its derivatives, and enables identification and visualization of non-covalent
5

interactions efficiently. The isosurfaces correspond to both favorable and unfavorable
interactions, as differentiated by the sign of the second density Hessian eigen value and defined
by the isosurface colour. NCI analysis allows an assessment of host-guest complementarities and
the extent to which weak interactions stabilize a complex. The information provided by NCI
plots is essentially qualitative, i.e. which molecular regions interact. The color scheme is a red-
yellow-green-blue scale with red for ρ+ (repulsive) and blue for ρ− (attractive). Yellow and
cut
cut
green surfaces correspond to weak repulsive and weak attractive interactions, respectively [27].
3. Results and discussions
3.1. Synthesis
Schiff base ligand HL was prepared by the condensation of N,N-dimethyl-1,3-
diaminopropane with 3-ethoxysalicylaldehyde following the literature method [28,29]. The
ligand was not isolated and the methanol solution of ligand was used directly for preparation of
the complex. The methanol solution of HL was reacted with methanol solution of cadmium(II)
acetate dihydrate followed by the addition of sodium azide under stirring condition to produce
the complex. The tetradentate Schiff base, HL, occupies four sites of the octahedral cadmium(II).
Exploiting bridging capacity phenoxo oxygen atoms and azides, a one-dimensional coordination
polymer, [{CdL(µ-1,1-N3)}2Cd(µ-1,1-N3)2·1.76CH3OH]n is formed. Synthesis of the complex is
shown in scheme 1.
6

Scheme 1: Preparation of complex.
3.2. Description of structure
3.2.1. [{CdL(µ-1,1-N3)}2Cd(µ-1,1-N3)2·1.76CH3OH]n
It crystallizes in the monoclinic space group C2/c. The asymmetric unit of complex
consists of a dinuclear cadmium(II) moiety { Cd(1) and Cd(2)} with a deprotonated tetradentate
Schiff base (L)- along with two end-on bridged azides. A lattice solvent molecule (MeOH) is also
present in the asymmetric unit near the origin of the unit cell and has been refined with
occupancy 1.76. It assumes chain structure having trinuclear cadmium(II) moieties as the
building blocks, in which the cadmium(II) centres {Cd(1)a, Cd(2) and Cd(1)} possess distorted
octahedral geometries. The perspective view of the trinuclear moiety is shown in Figure 1. The
Cd(2) is coordinated by two phenoxo oxygen atoms, O(5) and O(5)a, two ethoxy oxygen atoms,
O(6) and O(6)a, from two different tetradentate deprotonated Schiff bases and two end-on
bridged azide nitrogen atoms, N(1Z) and N(1Z)a {Symmetry transformation a = 1-x,y,1/2-z}. The
environment around Cd(1)a centre is very similar to that of the Cd(1) centre. Cd(1)a is
coordinated by two nitrogen atoms, N(1)a and N(5)a, and an oxygen atom, O(5)a, of a tetradentate
deprotonated Schiff base and two end-on bridging azide nitrogen atoms, N(4Z)a and N(1Z)a. On
the other hand, Cd(1) is coordinated by two nitrogen atoms, N(1) and N(5), and an oxygen atom,
O(5), of a second molecule of tetradentate deprotonated Schiff base and two end-on bridged
azide nitrogen atoms, N(4Z) and N(1Z). Symmetry related nitrogen atoms, N(4Z)b and N(4Z)c,
from two different end-on bridged azides, coordinate Cd(1)a and Cd(1), respectively to grow the
polymer (Figure 2). {Symmetry transformations b = x,1-y,-1/2+z; c = 1-x,1-y,1-z}. Selected bond
lengths and angles are gathered in Tables 2 and 3, respectively.
7

The angle between Cd(1)aO(5)aN(1Z)aCd(2) and Cd(2)O(5)Cd(1)N(1Z) rhombohedral
plane is 74.44°. The N(1)a-Cd(1)a-N(5)a and N(1)-Cd(1)-N(5) angles are 81.45(5)° and are
typical of a six membered chelate ring [30,31]. The Cd-Nimine distance {2.301(1) Å} is shorter
than the Cd-Namine {2.384(1) Å} distances, as were also observed in similar systems [30-33]. The
distance between Cd(1)a···Cd(2), Cd(2)a···Cd(1) and Cd(1)a···Cd(1) are 3.6499(4), 3.6499(4)
and 6.6944(6) Å, respectively. The bridging azides are quasi-linear; the N-N-N angles are
179.0(2)º and 179.5(2)º, as were also observed in similar systems [32,33].
3.3. IR, electronic and fluorescence spectra
In IR spectrum of the complex, strong band corresponding to the azomethine (C=N)
stretching vibration appears at 1636 cm-1. The presence of bridging azides is indicated by the
sharp bifurcated bands within 2072-2038 cm-1 range [34]. Bands in the range of 2993-2842 cm-1
are assigned due to alkyl C-H bond stretching vibrations are customarily noticed In IR spectrum
of the complex [32,33]. Broad bands in the range of 3518-3374 cm-1 may be assigned as O-H
stretching vibrations [35,36].
Electronic spectrum of complex exhibits three bands of which high energy bands around
266 and 332 nm may be attributed to π-π* and n-π* transitions and last band at 421 nm assigned
as ligand to metal charge transfer transition (LMCT) [37,38]. The complex exhibits
luminescence in DMSO medium at 332 nm on exciting at 394 nm, which may be assigned to the
intra-ligand (π-π*) fluorescence [39]. The average lifetime of the excited state is 9.72 ns (Table
4) and decay profile is shown in Figure 3. Relative fluorescence quantum yield for the complex
was measured following the literature method [35,40] and the value is found to be 0.1461.
8

3.4. Photocatalytic activity
The distinct performance on the photocatalytic degradation of an organic dye, methylene
blue, was discovered in the complex in an aqueous solution under visible light irradiation. As
shown in Figure 4, the residual concentration of the dye in an aqueous solution gradually
decreased as a function of the increasing reaction time, indicating that the complex can degrade
the organic dye. With increase in complex concentration, the rate of degradation was also
increased (Figure 4).
The complex is highly efficient for the degradation of MB and the ratio of the
degradation reaches about 68% using only 1 mg of the complex (Figure 4, curve III). Use of 3
and 4.8 mg of the complex, the ratio of the degradation reaches about 82 and 86 %, respectively
(Figure 4, curves IV,V). The ratio of the degradation reaches about 99 % using 7 mg of the
complex (Figure 4, curve VI). To prove the high photocatalytic efficiency of the complex to MB,
comparative experiments without catalyst under visible light irradiation were performed, which
showed only very little decomposition. We had also studied the photocatalytic activity of
cadmium(II) acetate hexahydrate to MB under similar conditions (Figure 4, curve II), which
showed that the rate of degradation was still very slow (only 16 % using 4 mg of bare
cadmium(II). Again, as shown in Figure 5, it is shown that the intensity of the characteristic
absorption peak of MB decreased with the increase of irradiation time in the degradation process.
The reaction depends on 1st Order Kinetics and the details data on average rate constants for this
degradation are given in Table 5. A probable mechanistic pathway for the photocatalytic
degradation of organic dye is shown in Scheme 2. At first, electrons (e−) of the complex were
excited from the valence band (VB) to the conduction band (CB) which leads to equal amounts
of positives vacancies (holes, h) left in VB. In the next step, oxygen (O2) or hydroxyl (OH−)
9

adsorbed on the surfaces of complex could interact with the electrons (e−) on the CB or the hole
(h) on the VB, respectively, which would probably lead to the formation of the hydroxyl radicals
(ȮH). Later on, the ȮH radicals could effectively degrade the methylene blue (MB) to carry out
the process. Similar mechanism has also been proposed by other groups [15]. The stability of the
complex as catalyst has been investigated by recording the IR spectrum of the complex after
photocatalytic reaction. The IR spectrum of the complex at the end of photocatalytic degradation
of MB is more or less identical with that of the original one (Figure 6), demonstrating the
stability of the complex after the photocatalytic process.
Scheme 2: Probable mechanistic pathway for the degradation of organic dye (MB).
3.5. DFT study on supramolecular interactions
The polymeric chain formed by the complex in the solid state is also common in many
cadmium(II) complexes. These polymeric chains can be viewed as trinuclear [Cd3L2(N3)2]2+
discrete units connected by azide bridges. In Figure 7, a fragment of the crystal structure is
showed where it is highlighted how these polymeric one-dimensional chains interact to each
other forming two-dimensional layers. Remarkably, the aromatic hydrogen atoms of ligands
10

(highlighted in Figure 7) are interacted by means of weak hydrophobic interactions with the
aliphatic groups of ligands belonging to the neighbour one-dimensional chain. Moreover, the
presence of MeOH molecules from the solvent is also important for connecting these polymeric
one-dimensional chains which also help to estabilise hydrogen bonding interactions, as further
described below. The purpose of this theoretical study is to emphasize the contribution of weak
long range interactions in the formation of the two-dimensional layer represented in Figure 7.
A discrete dimer has been taken from the X-ray structure where the infinite chains have
been reduced to the trinuclear [Cd3L2(N3)2]2+ repeating unit and have been computed by means
of DFT calculations (BP86-D3/def2-TZVP) (see Figure 8). Moreover, two azide ligands
belonging to the double azide bridge have been included to compensate the positive charge. The
octahedral coordination environment of the cadmium atom has been completed by neutral HCN
ligand (see small arrows in Figure 8b). The interaction energy of this dimer (∆E1 = -10.0
kcal/mol) is considerably large taking into consideration that only weak C-H···H-C and other
long range van der Waals (vdW) interactions are present. In order to evaluate the role of the
MeOH molecules connecting the one-dimensional chains, The interaction energy of this dimer
has also been computed with two methanol molecules. Each MeOH molecule has established
two hydrogen bonding interactions (see red dashed lines in Figure 8c), one as donor (with the
azide ligand) and other as acceptor (with an aromatic C-H). The binding energy that results from
the interaction of this dimer with two solvent molecules is ∆E2 = -21.8 kcal/mol that corresponds
to the contribution of the four hydrogen bonds. As expected, the role of the MeOH is crucial
connecting the one-dimensional chains; however the long range interactions (∆E1) are not
negligible and they are also important to explain the final solid state architecture of the polymer.
11

In order to characterize the weak van der Waals interactions shown in Figure 8b, the non-
covalent interaction (NCI) plot of this model dimer has been computed also. The NCI plot is a
visualization index that enables identification and visualization of non-covalent interactions
efficiently. The representation of the NCI plot computed for the dimer of the complex is shown
in Figure 9. An extended region can be observed between the aromatic and aliphatic C-H bonds.
The presence of this extended region explains the large interaction energy, since it includes the
contribution of many weak long range C-H···H-C contacts.
4. Summary
In conclusion, we have synthesized a polynuclear end-on azide bridged octahedral
cadmium(II) Schiff base complex and characterized by elemental, spectral and single crystal X-
ray diffraction analysis. The complex exhibits extremely highly efficient photocatalytic
decomposition of methylene blue in visible light. This is the first example of any ray
characterized cadmium(II) Schiff base complex with photocatalytic application. These results
provide an opening into a promising new field of the highly efficient photocatalytic degradation
of organic pollutant. We are now working hard to get better yield of the reaction and to
synthesize other photocatalytic cadmium(II) complexes.
Acknowledgements
A.B. and A.F. thank DGICYT of Spain (projects CTQ2014-57393-C2-1-P and CONSOLIDER
INGENIO CSD2010-00065, FEDER funds) for funding. We thank the CTI (UIB) for free
allocation of computer time.
12

Appendix A. Supplementary data
Crystallographic data for the analysis have been deposited with the Cambridge
Crystallographic data Centre, CCDC No 1478964. The data can be obtained free of charge from
CCDC via www.ccdc.cam.ac.uk/data_request/cif.
13

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Reference Material: Quinine Sulfate Dihydrate, National Bureau of Standards Special
Publication 260-64, National Bureau of Standards, Washington, DC (1980).
16

Table 1: Crystal data and refinement details of complex.
Formula
Formula Weight
Temperature (K)
Crystal system
Space group
a(Å)
C29.76H49.04Cd3N16O5.76
1060.40
100
Monoclinic
C2/c
21.4706(8)
9.9542(4)
19.3257(7)
103.7819(11)
4
b(Å)
c(Å)
β(°)
Z
dcalc (g cm-3)
µ(mm-1)
1.756
1.637
F(000)
2118.7
Total Reflections
Unique Reflections
Observed data[I >2 σ (I)]
No. of parameters
R(int)
40107
4629
4298
279
0.024
R1, wR2 (all data)
R1, wR2 [I > 2 σ (I)]
0.0188, 0.0392
0.0163, 0.0382
17

Table 2: Selected bond lengths (Å) of complex.
Cd(1)–O(5)
2.3290(11)
2.3845(13)
2.3448(14)
2.333(2)
Cd(1)–N(1)
Cd(1)–N(1Z)
Cd(1)–N(4Z)
Cd(1)–N(5)
2.3015(14)
2.318(2)
Cd(1)–N(4Z)c
Cd(2)–O(5)
2.2187(11)
2.3941(11)
2.2854(13)
2.2187(11)
2.3941(11)
2.2854(13)
Cd(2)–O(6)
Cd(2)–N(1Z)
Cd(2)–O(5)a
Cd(2)–O(6)a
Cd(2)–N(1Z)a
Symmetry transformations a = 1-x,y,1/2-z; c = 1-x,1-y,1-z.
18

Table 3: Selected bond angles (°) of complex.
O(5)–Cd(1)–N(1)
100.13(4)
72.90(4)
168.15(6)
77.38(4)
93.55(6)
92.99(5)
91.38(6)
81.45(5)
164.97(6)
103.89(7)
148.29(5)
97.00(7)
107.42(7)
75.36(7)
95.61(7)
68.79(4)
76.10(4)
178.56(4)
112.43(4)
103.05(4)
138.47(4)
112.43(4)
75.77(4)
98.72(4)
103.05(4)
98.72(4)
110.46(5)
68.79(4)
76.10(4)
138.47(4)
O(5)–Cd(1)–N(1Z)
O(5)–Cd(1)–N(4Z)
O(5)–Cd(1)–N(5)
O(5)–Cd(1)–N(4Z)c
N(1)–Cd(1)–N(1Z)
N(1)–Cd(1)–N(4Z)
N(1)–Cd(1)–N(5)
N(1)–Cd(1)–N(4Z)c
N(1Z)–Cd(1)–N(4Z)
N(1Z)–Cd(1)–N(5)
N(1Z)–Cd(1)–N(4Z)c
N(4Z)–Cd(1)–N(5)
N(4Z)–Cd(1)–N(4Z)c
N(4Z)c–Cd(1)–N(5)
O(5)–Cd(2)–O(6)
O(5)–Cd(2)–N(1Z)
O(5)–Cd(2)–O(5)a
O(5)–Cd(2)–O(6)a
O(5)–Cd(2)–N(1Z)a
O(6)–Cd(2)–N(1Z)
O(5)a–Cd(2)–O(6)
O(6)–Cd(2)–O(6)a
O(6)–Cd(2)–N(1Z)a
O(5)a–Cd(2)–N(1Z)
O(6)a–Cd(2)–N(1Z)
N(1Z)–Cd(2)–N(1Z)a
O(5)a–Cd(2)–O(6)a
O(5)a–Cd(2)–N(1Z)a
O(6)a–Cd(2)–N(1Z)a
Symmetry transformations a = 1-x,y,1/2-z; c = 1-x,1-y,1-z.
19

Table 4: The details data of the photoluminescence and time-resolved photoluminescence
decays of the complex.
λex(nm)
λem(nm)
A1(%)
90.14
τ1(ns)
A2(%)
9.86
τ2(ns)
τav(ns)
χ2
332
394
10.01
3.62
9.72
1.0188
Table 5: The details data of the rate constants for the degradation of organic dye.
Average rate constant
Amount of complex (mg) taken in 10
mg L-1 aqueous solution of MB
1
3
5
7
3.56 x 10-3
5.07 x 10-3
5.39 x 10-3
4.81 x 10-3
20

Figure 1: Trinuclear moiety of complex with selective atom-numbering scheme. Non-
coordinated methanol molecule and hydrogen atoms are omitted for clarity. Symmetry
transformations a = 1-x,y,1/2-z; b = x,1-y,-1/2+z; c = 1-x,1-y,1-z.
21

Figure 2: Polymeric chain of the complex with selective atom-numbering scheme showing only
the coordinated atoms and bridging azides. Symmetry transformations a = 1-x,y,1/2-z; b = x,1-y,-
1/2+z; c = 1-x,1-y,1-z.
22

Figure 3: Lifetime decay profile of the complex.
23

Figure 4: Changes in concentration of MB as a function of reaction time in the presence of
different amount of complex (curves III-VI), without complex (curve I), and with Cadmium-salt
(curve II), under visible light irradiation.
24

Figure 5: UV-VIS absorption spectra of MB solution with the complex (sample taken = 5 mg),
used as a catalyst.
25

Figure 6: IR spectra of the complex before (green) and after photodegradation (blue) process
26

Figure 7:Two-dimensional layers of the complex.
27

Figure 8: (a) Fragment of the X-ray structure of the complex; (b) Theoretical model of the
dimer; (c) Hydrogen bonding interactions of the MeOH with the dimer. Distances in Å.
28

Figure 9: NCI plot of the self-assembled dimer of the complex. NCI plot only shows the
intermolecular interactions.
29