Schiff base and azido coordinated di-/poly-nuclear cadmium(II) complexes: Crystal structure, photocatalytic degradation of methylene blue and thermal analysis

Article abstract of DOI:10.1016/j.poly.2019.114296

Two Schiff base coordinated cadmium(II) complexes, namely [Cd(H₄L¹)(N₃)₂]_n (1) and [Cd₂(L²)(N₃)₂]·(H₂O) (2) (where H₄L¹ = 2

Full text of DOI:10.1016/j.poly.2019.114296

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Schiff base and azido coordinated di-/poly-nuclear cadmium(II) complexes:
Crystal structure, photocatalytic degradation of methylene blue and thermal
analysis
Soumen Manna, Ennio Zangrando, Subal Chandra Manna
PII:
S0277-5387(19)30741-7
DOI:
https://doi.org/10.1016/j.poly.2019.114296
POLY 114296
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16 November 2019
Please cite this article as: S. Manna, E. Zangrando, S.C. Manna, Schiff base and azido coordinated di-/poly-nuclear
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Schiff base and azido coordinated di-/poly-nuclear cadmium(II) complexes:
Crystal structure, photocatalytic degradation of methylene blue and thermal
analysis
Soumen Manna,a Ennio Zangrando,b Subal Chandra Mannaa,*
aDepartment of Chemistry, Vidyasagar University, Midnapore 721102, West Bengal, India, E-
mail: scmanna@mail.vidyasagar.ac.in, Fax: (91) (03222) 275329.
bDepartment of Chemical andPharmaceutical Sciences, University of Trieste, 34127 Trieste,
Italy.
Abstract
Two Schiff base coordinated cadmium(II) complexes, namely [Cd(H4L1)(N3)2]n(1)and
[Cd2(L2)(N3)2]·(H2O) (2) (where H4L1=2-((2-hydroxy-3-methoxybenzylidene)amino)-2-
(hydroxymethyl)-propane-1,3-diol; andH2L2 = bis((3-methoxysalicylidene)ethyl)ethylamine),
were synthesized and characterized by X-ray single crystal diffraction. Both the complexes 1 and
2 crystallize in monoclinic system with space group P 21/n. Complex 1 is a 1D coordination
polymer where Cd(H4L1)species are doubly connected by bridging μ-1,1 azide anions. Complex
2 is a discrete dinuclear compound where the double deprotonatedSchiff base (L2)2- acts as a two
compartmental ligandcoordinating two cadmium atoms. Photocatalytic activity of the complexes
has been studied using UV-vis absorption spectroscopic technique and the results show that both
the complexes are active for photocatalytic degradation of methylene blue (MB) in presence of
UV light, and within180 min MB decomposed by 37.64% and 32.60% in presence of complexes
1 and 2, respectively.
Keywords: Cadmium(II); Schiff base; Coordination polymer; Crystal structure; Photocatalyst

1. Introduction
The design and synthesis of coordination compounds of group 12 metal complexes are of great
interest because of their functional behavior, due to their wide varieties of structures [1-2]and
potential application in the area of material science [3-4]. In addition, these coordination
compounds are well known in the literature for their interesting photophysical and
photochemical properties which allow their potential use as luminescent probes, light emitting
diodes and photovoltaic devices [5].For these purposes Schiff bases with different polydentate
coreare potential ligands for the synthesis of cadmium(II) coordination compounds, andthe
combined use of chelating Schiff base and linear bridging ligands is an efficient strategy for the
design of polynuclear cadmium(II) species [6].
Removal of highly toxic organic pollutants from the wastewater is an important area of
current research [7]. Organic dyes in the industrial waste water are very toxic since these
pollutants remain in water for long time. Photocatalytic degradation of organic dye is a useful
technique for the treatment of industrial wastewater. TiO2 is well known photocatalyst for the
degradation of organic dye in presence of UV-visible light. However, post separation of
TiO2catalyst is very difficult after treatment of wastewater, causing limitation of theuse of TiO2
as catalyst [8]. Recently coordination compounds have attracted great interestfor the study of
photocatalytic degradation of organic dyes in water and still represents a big challenge [9-10].
Literature survey reveals that Schiff base coordinated cadmium(II) species show photocatalytic
activity for the degradation of organic dyes [6].
In the present contribution we have used two Schiff bases, namely2-((2-hydroxy-3-
methoxybenzylidene)amino)-2-(hydroxymethyl)-propane-1,3-diol
(H4L1)
and
bis((3-
methoxysalicylidene)ethyl)ethylamine) (H2L2), in combination with azide ligands to synthesize

two cadmium complexes, [Cd(H4L1)(N3)2]n (1) and [Cd2(L2)(N3)2]·(H2O) (2). Both the
compounds 1 and 2 are active for photocatalytic degradation of methylene blue in presence of
visible light.
2. Experimental
2.1. Materials and physical measurements
Tris(2-aminoethyl)aminewas purchased from the Sigma-Aldrich and used as received. All other
chemicals were of AR grade, and the reactions were performed under aerobic conditions. The
solvents used for spectroscopic studies were purified and dried by standard procedures before
use [11].
Elemental analyses (carbon, hydrogen, and nitrogen) were performed with a Perkin–Elmer 240C
elemental analyzer. The IR spectra were recorded with samples as KBr pellets with a Bruker
Vector 22 FTIR spectrophotometer operating in the wavenumber range from400 to 4000 cm–1.
The electronic absorption spectra were obtained at room temperaturewith aShimadzu UV-
1601spectrophotometer. Quartz cuvette of 1 cm path length and 3 cm3volume was used for all
measurements. Emission spectra were recorded on a Hitachi F-7000 spectrofluorimeter. The X-
ray powder diffraction (PXRD) data were collected from Bruker D2 phaser X-ray diffractometer
(30 kV, 10 mA), employing Mo-Kα (λ=0.71073Å) radiation at room temperature.
Thermogravimetric analyses (TGA) were carried out with a TGA Q50 V20.13 Build 39
instrument under N2 atmosphere. Mass spectra of complexes 1 and 2 were performed using
ultraflexTOF/TOF instrument in water.

2.2. Crystallographic Data Collection and Refinement
Intensity data collection for complexes 1-2 was carried out at room temperature with a Smart
Apex-II, Bruker AXS diffractometer equipped with CCD and Mo-Kα radiation (λ = 0.71073 Å).
Cell refinement, indexing and scaling of the data sets were done by using the Apex-II package
[12]. The structures were solved by direct methods and subsequent Fourier analyses [13] and
refined by the full-matrix least-squares method based on F2 with all observed reflections [13].
The CH2-OH groups of complex 1 have been refined with a constrained C-O distance of 1.43(1)
Å due to the disorder detected in the oxygen atoms. In compound2a lattice water molecule was
located in the Fourier map.Hydrogen atoms were placed at calculated positions. Publication
material and calculations were performed by using WingX program Version 2013.3,[14] and
Diamond [15].Crystal data and details of refinements for the two compounds are given in Table
1.
2.3. Synthesis
Complexes 1 and 2 have been synthesized adopting procedures which are schematically
displayed in Scheme 1.

Scheme 1. Synthesis of complexes 1 and 2.
2.3.1. Synthesis of [Cd(H4L1)(N3)2]n (1)
The polydentate ligand H4L1was prepared by refluxing 2-hydroxy-3-methoxy benzaldehyde (1
mmol, 0.152 g) and tris(hydroxymethyl)amino methane (1 mmol, 0.121 g) in methanol (10 mL)
following the reported method [15]. A methanolic solution (10 mL) containing H4L1 (0.09 gm,
0.5 mmol) and Et3N (0.05 gm, 0.5 mmol) was added to 10 mL of methanol containing
Cd(NO3)2.4H2O (0.154 g, 0.5 mmol) under stirring condition. To this reaction mixture, 2 ml of
aqueous solution of sodium azide (0.032 gm, 0.5 mmol) were added and stirred for additional 2
h. The yellow colored solution was filtered and left at room temperature. Yellow colored crystals
suitable for X-ray diffraction were obtained after a few days. Yield: 66%. Anal. Calcd for
C12H17CdN7O5 (451.74 g mol–1): C, 31.90; H, 3.79; N, 21.70 %. Found: C, 31.92; H, 3.76; N,
21.73 %. Selected FTIR bands (KBr, cm-1; vs = very strong, s = strong, m = medium, w = weak,

br = broad): 3373 (br), 2946 (w), 2894 (w), 2038 (vs), 1632 (vs), 1545 (s), 1498 (vs), 1338 (s),
1288 (s), 1220 (vs), 1165 (s), 1039 (vs), 959 (w), 891 (s), 774 (vs), 733 (vs), 657 (s), 606 (s).
UV-vis spectra [λmax, nm (ε, L mol-1cm-1)] (CH3OH solution) 227 (5.689×104), 236 (5.719×104),
266 (2.829×104), 292 (3.642×104), 416 (1.535×104).
2.3.2. Synthesis of [Cd2(L2)(N3)2]·(H2O) (2)
The Schiff base ligand H4L2was prepared by stirring a methanolic solution(20 mL) of 2-hydroxy-
3-methoxybenzaldehyde (0.152 g, 1 mmol) and tris(2-aminoethyl)amine (0.073 g, 0.5 mmol) for
1 h at room temperature. Then Cd(OAc)2·2H2O (0.133 g, 0.5 mmol) dissolved in methanol was
added to a methanolic solution of H4L2 (0.207 g, 0.5 mmol) and Et3N (0.1 g, 1 mmol) and stirred
for 2 hrs. To this resultant solution, 2 mlof aqueous solution of sodium azide (0.032 gm, 0.5
mmol) were added and the stirred for additional 1 h. The yellow colored solution was filtered
and left at room temperature. Colorless crystals suitable for X-ray diffraction were obtained after
a few days. Yield: 72%. Anal. Calcd for C22H30Cd2N10O5 (739.37 g mol–1): C, 35.73; H, 4.08; N,
18.94%. Found: C, 35.75; H, 4.10; N, 18.91%. Selected FTIR bands (KBr, cm-1; vs = very
strong, s = strong, m = medium, w = weak, br = broad): 3333 (s), 2896 (w), 2856 (w), 2039 (vs),
1631 (vs), 1598 (vs), 1549 (s), 1448 (vs), 1405 (s), 1333 (w), 1301 (vs), 1238 (vs), 1211 (vs),
1155 (w), 1074 (vs), 1030 (s), 959 (vs), 905 (s), 846 (vs), 782 (s), 739 (vs), 625 (vs), 509 (w).
UV-vis spectra [λmax, nm (ε, L mol-1cm-1)] (CH3OH solution) 232 (1.818×105), 271 (8.338×104),
357 (3.552×104).
2.4. Photocatalytic Measurement

The photocatalytic activity of complexes 1 and 2 were studied out using 10 μM aqueous solution
of methylene blue (MB). A 125 W mercury vapour lamp was used as the source of UV light and
photocatalytic degradation experiment was carried out with a solution of MB where catalyst
concentration is 1 gm L-1. The mixture of solution containing MB and catalyst was stirred
continuously under UV light and a 4 ml of the irradiated solution was taken after 20 mins
interval, and recorded the absorption spectra. The characteristic electronic absorption band at 660
nm of MB was used to examine the photocatalytic degradation process.
3. Result and Discussion
3.1. Crystal structure description
3.1.1. [Cd(H4L1)(N3)2]n(1)
The structural analysis of compound 1 shows a coordination polymeric complex where Cd(H4L1)
units are doubly connected by bridging μ-1,1 azide anions. The metal exhibits a highly distorted
octahedral coordination sphere where the Schiff base chelates the Cd atom through the methoxy
and phenolato oxygen donor, so that all the hydroxyl groups result uncoordinated (Fig.1). The
ligand appears neutral in its zwitter ionic form, being the imino nitrogen protonated and not
involved in coordination. An intramolecular hydrogen bond interaction (N7…O1 = 2.597 Å, N-
H…O1 = 136.74°) can be seenfor1. Cd complexes with a 2-methoxy Schiff base that acts as
chelating agent through methoxo and phenoxo oxygens and uncoordinated imino nitrogen have
been reported [16].
The Cd-O bond lengths are significantly different, being the Cd-O1 (phenoxo) of 2.216(5) Å and
that involving the methoxy oxygen of 2.487(5) Å. The Cd-N bond distances fall in the range
2.292(6) - 2.366(6) Å, in agreement with similar structures reported [16]. In the polymeric chain

the Cd atoms are alternatively separated by 3.716Å and 3.734 Å with an intermetallic angle of
−
129.22°. The zig-zag arrangement of the chain and the bridging N3 anions lead to coordination
bond angles far from ideal octahedral values (Table 2) and the smaller N(1)-Cd-N(1') and larger
N(4)-Cd-O(2) values are 73.5(2)° and 149.7(2)°, respectively. A similar coordination polymer
[Cd(-1,1-N3)2]n [17] has been reported with metals coordinated by N,N-dimethyl-1,3-
diaminopropane ligand having a Cd-Cd distance of 3.839 Å.
The crystal packing of present complex shows interdigitated polymers connected by short -
interactions involving phenyl rings (alternated distance of 3.347(4)Å and 3.407(4) Å between
centroids), and weak hydrogen bonds among the alcoholic groups O17-H and O15(at x-1, y, z)
[O…O = 2.811 Å, O-H…O= 147.1°] although the high degree of thermal motion indicates a
positional disorder of hydroxyl oxygen atoms(Fig. 2).
3.1.2. [Cd2(L2)(N3)2]·(H2O) (2)
Tripodal Schiff base ligands having three equal groups attached to the tertiary amine nitrogen
have been alreadyreported [18], but most of these have been employed to study properties of
lanthanide complexes. Here an asymmetric tripodal molecule H2L2 (H2L2 = bis((3-
methoxysalicylidene)ethyl)ethylamine) as target ligand was synthesized with the aim to react
with Cd2+ ions.
Compound 2 crystallizes in monoclinic system, space group P21/n, as discrete dinuclear
complexalong with a lattice water molecule. The anionic organic species (L2)2- acts as a two
compartmental ligand coordinating two cadmium atoms where phenoxo oxygen atoms act as
bridging donors towards the metals that are separated by 3.638 Å (Fig.3). Both metals exhibit a
six-coordination geometry.Cd1 is coordinated by the imino and amino nitrogen donors and by

the phenoxy oxygens in highly distorted pentagonal pyramid coordination geometry where the
amino nitrogen N4 is located at the apex. Cd2, beside the bridging phenoxo oxygens, is
coordinated by the methoxy groups, and completes the distorted trigonal prismatic environment
with azide anions.
The Cd1–N bond distances are in the range of 2.2701(18)-2.5707(18) Å and Cd1–Ophen are
of2.2975(15)Å and 2.3187(15) Å. On the other hand, the Cd2-O bond lengths fall in between
2.2325(15)-2.5167(15) Å, and Cd2-N are of 2.210(2)Å and 2.199(2) Å, the latter is the shortest
among those reported. The deviations from an octahedral geometry are clearly shown by the
values of bond angles reported in Table 3. The Cd-O-Cd bridging angles average to 105.77°,
while the terminal coordinated azides form a N-N-Cd2 angle of 125.79° (mean value). In order
to accomplish coordination with all donor atoms, the ligand assumes a conformation where
phenol moiety ringsareslightly bent to form a dihedral angle of 20.12° (Fig.4).These geometrical
parameters are in agreement to those reported in the dinuclear complex [Cd(L´)2Cd(N3)2] (HL´ =
2-((3-(dimethylamino)propylimino)methyl)-6-methoxyphenol) formed by two Schiff bases, but
having a similar core and coordination set for the metals [17].
The crystal packing shows the metal complexes connected by H-bonds (Fig.5) involving
nitrogens of symmetry related azide anions and the water molecule (O5…N5 = 2.947(3), O5-
H…N5 = 166°, O5…N10 = 2.945(3) Å, O5-H…N5 = 167°). In addition,terminalazideatom N10
weakly interacts with amine group N4 of a symmetry related complex (N10…N4 = 3.072(4) Å).
3.2. FTIR spectra of complexes 1 and 2
The IR spectral band for 1 and 2(Table 1S, Fig.1S)at 1632 cm-1 and 1631 cm-1, respectively, is
due to the azomethine (C=N) group. The band at 2946 cm-1 (for 1) and 2896 cm-1 (for 2)is due to

aromatic C-H stretching vibration; while aliphatic ν(C-H) stretching vibration for 1 and 2
appears at 2894 and 2856 cm-1, respectively. Bands at 1165 cm-1 (for 1) and 1155 cm-1(for 2) are
assigned to ν(O–CH3) stretching vibration. Asymmetric structure vibration for azido group
(νas(N3)) appears at 2038 and 2039 cm-1 for complexes 1 and 2, respectively. IR spectroscopic
technique is an important tool to identify the types of bonding, end-on/end-to-end, present in a
compound. It is to note that azido bridged cadmium compounds show major tendency to form
end-on bridging mode in comparison to the end-to-end bridging mode. Like 1 and 2, the reported
complexes [Cd2(MeDPA)2(μ1,1-N3)2(N3)2], [Cd(3-ampy)(μ1,1-N3)2]n, [Cd(8-aminoql)(μ1,1-N3)2]n
and [Cd(3,5-daba)(μ1,1-N3)2]n [19]also exhibit end-on bonding modes and their νas(N3) stretching
vibrations are very close to the reported ionic azide in KN3 (2039 cm−1).
3.3. Electronic and emission spectra of complexes 1 and 2
The electronic absorption spectra of complexes 1 and 2 have been recorded in methanol (Table
2S, Fig.2S). Compound 1 shows significant transitions at 227 (5.689×104 L mol−1 cm−1), 236
(5.719×104 L mol−1 cm−1), 266 (2.829×104 L mol−1 cm−1), 292 (3.642×104 L mol−1 cm−1) and 416
(1.535×104 L mol−1 cm−1) and compound 2 shows transitions at 232 (1.818×105 L mol−1 cm−1),
271 (8.338×104 L mol−1 cm−1) and 357 (3.552×104 L mol−1 cm−1).
On excitation at 236 nm, compound 1 exhibits a luminescence band at 307 nm in methanol at
room temperature and compound 2, on excitation at 232 nm shows an emission band at 305 nm
(Fig. 3S).
3.4. PXRD and Thermogravimetric Analysis

The powder X-ray diffraction (PXRD) patterns of complexes 1 and 2 are coincident with the
simulated diffraction pattern obtained from the single crystal XRD data, suggesting that the bulk
samples are same as the single crystals used for structural analysis. (Fig.4S-5S). The differences
in intensity between synthesized compound and simulated pattern from single crystal of
complexes may be due to favored orientation of the crystalline powder samples [20].
The thermogravimetric analysis (TGA) of 1-2was investigated under a nitrogen atmosphere and
shown in Fig.6.For complex 1, initial weight loss begins at 202°C and continues in one step up to
246°C. The total weight loss over this range is 20.47%, which corresponds to the loss of organic
component. TGA curve for complex 2 exhibits weight loss in two steps. In the first step the
weight loss of 2.29% below 100°C is assigned to the loss of lattice water (calcd 2.43%). The
second step of 13.56% weight loss in the range 265-296°C is attributed to loss of organic
component present in the crystalline compound.
3.5. Photocatalytic activity
Photocatalytic activities of complexes 1 and 2 have been studied by photodegradation of
methylene blue (MB). Methylene blue is an organic dye and it is widely used in industry for the
synthesis of various textile and painting materials. The photo-catalytic degradation of methylene
blue was studied using UV light and progress of the reaction studied using UV-vis absorption
spectroscopic technique. Before irradiation, 10 μM, 50 μL aqueous solution of methylene blue
(MB) was added to the aqueous solution of complexes 1 and 2to maintain a catalyst
concentration of 1g L-1.Aqueous solution of methylene blue shows characteristic absorption band
at 660 nm (Fig.6S). In presence of complexes 1 and 2, the absorbance of 660 nm band of

methylene blue gradually decreased with time. The change in the electronic absorption spectra of
MB in presence of complexes under study after 180 min is shown in Figs.7-8.
To determine the kinetics of photocatalytic degradation of MB by complexes 1 and 2, the UV-vis
titration spectral data have been analyzed by using Langmuir-Hinshewood model as described by
ln(Ct/C0) = −Kappt
or, ln(At/A0) =−Kappt
Where Ct and C0= concentration of dye at time t and at t=0, respectively, At and A0 = absorbance
of dye at time t, and at t=0, respectively, Kapp = apparent rate constant.
The ln(C0/Ct) vs t plot gives a straight line passing through origin, and the slope of the lines
furnishes the value of apparent rate constant (Fig.9). Calculated values of rate constant for 1 and
2 are 2.63×10-3 and 2.45×10-3 min-1, respectively.
Percentage of decomposition of dye was calculated using the equation
Dye removal (%) = C −Ct × 100
0
C
0
A −A
0
=
t × 100
A
0
Calculated results show that after 180 min, the dye decomposed by 37.64% and 32.60% in
presence of complex 1 and 2, respectively. It is worth of note that there is no noticeable change
of intensity of MB band at 660 nm in absence of complexes 1 and 2even after 180 min (Fig.9).
This indicates that complexes 1 and 2 play a fundamental role for decomposition of the dye. A
comparison (Table 4) of results of Cd(II) coordination compound catalyzed photocatalytic
degradation of MB indicates that 1 and 2 are less efficient photo-catalyst in contrast to the
previously reported compounds.

4. Conclusion
In summary, we have presented here the synthesis, crystal structure, thermal analysis and
photocatalytic activities of two azido coordinated cadmium(II) complexes using 2-((2-hydroxy-
3-methoxybenzylidene)amino)-2-(hydroxymethyl)-propane-1,3-diol
(H4L1)
and
bis((3-
methoxysalicylidene)ethyl)ethylamine) (H2L2). Cadmium(II)-azido in combination with H4L1
and H2L2results 1D coordination polymer (1) and discrete dinuclear compound (2). 2D
supramolecular structure of complex 1 is formed with H-bonding and π-π interactions. On the
other hand complex 2 forms1D supramolecular chain like structure with H-bonding interactions.
Both the complexes are active for UV-light-driven photocatalytic degradation of methylene blue
(MB).
Acknowledgements
The authors gratefully acknowledge the financial assistance given by the CSIR, Government of
India, to Dr. Subal Chandra Manna (Project No. 01 (2743)/13/EMR-II). Dr. S. C. Manna thanks
UGC-SAP and DST-FIST New Delhi and Vidyasagar University for infrastructural facilities.
Supplementary information
CCDC 1947104 and 1947105 contain the supplementary crystallographic data for complexes 1
and 2, respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/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. IR, photophysical parameters, UV-vis absorption spectra, PXRD
patterns.
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Table 1. Crystal data and details of structure refinement of complexes 1 and 2.
Complex
1
2
Empirical formula
C12H17CdN7O5
C22H30Cd2N10O5
Formula mass, g mol–1 451.72
739.36
Crystal system
Space group
a, Å
Monoclinic
Monoclinic
P 21/n
P 21/n
6.7305(6)
10.1895(9)
23.972(3)
96.428(9)
1633.7(3)
4
15.3991(14)
9.0213(12)
19.9725(15)
107.702(11)
2643.2(5)
4
b, Å
c, Å
β, deg
V, Å3
Z
D(calcd), g cm–3
(Mo-Kα), mm–1
F(000)
1.837
1.858
1.378
1.663
904
1472
Theta range, deg
No. of collected data
No. of unique data
Rint
3.07 - 28.87
7427
1.99 - 26.41
20361
3805
5364
0.0358
0.0208
Obs reflects [I> 2σ(I)] 2364
4935
Goodness of fit (F2)
1.111
228
1.028
Parameters refined
354
R1, wR2 (I >2σ(I)) [a]
R1, wR2 (all data)
Residuals, e Å–3
0.0617, 0.1280
0.1050, 0.1543
0.995, –0.759
0.0205, 0.0472
0.0232, 0.0484
0.693, –0.481

Table 2. Coordination bond lengths (Å) and angles (°) for complex 1 (the Cd atom is located on a
two-fold axis).
Cd-O(1)
Cd-O(2)
Cd-N(1)
2.216(5)
2.487(5)
2.367(6)
Cd-N(1')
Cd-N(4)
Cd-N(4'')
2.292(6)
2.307(6)
2.366(6)
N(1)-Cd-N(1')
N(4)-Cd-N(4'')
O(1)-Cd-O(2)
O(1)-Cd-N(1')
O(1)-Cd-N(4)
N(1')-Cd-N(4)
O(1)-Cd-N(1)
73.5(2)
74.7(2)
N(4)-Cd-N(1)
O(1)-Cd-N(4'')
N(1')-Cd-N(4'')
N(1)-Cd-N(4'')
N(1')-Cd-O(2)
N(4)-Cd-O(2)
N(1)-Cd-O(2)
N(4'')-Cd-O(2)
96.5(2)
110.8(2)
94.4(2)
159.9(2)
85.0(2)
149.7(2)
109.6(2)
84.72(19)
68.33(16)
140.6(2)
98.2(2)
118.0(2)
88.16(19)
Symmetry codes: (') -x, -y, -z+1; ('') -x+1, -y, -z+1.
Table 3. Coordination bond lengths (Å) and angles (°) for complex 2
Cd(1)-O(2)
Cd(1)-O(3)
Cd(1)-N(1)
Cd(1)-N(2)
Cd(1)-N(3)
Cd(1)-N(4)
2.2975(15) Cd(2)-O(1)
2.3187(15) Cd(2)-O(2)
2.2701(18) Cd(2)-O(3)
2.5707(18) Cd(2)-O(4)
2.2948(18) Cd(2)-N(5)
2.4534(15)
2.2325(15)
2.2779(15)
2.5167(15)
2.210(2)
2.306(2)
Cd(2)-N(8)
2.199(2)
N(1)-Cd(1)-N(3) 110.95(7) N(8)-Cd(2)-N(5) 115.07(8)
N(1)-Cd(1)-O(2) 79.63(6) N(8)-Cd(2)-O(2) 111.12(7)
N(3)-Cd(1)-O(2) 143.62(6) N(5)-Cd(2)-O(2) 119.11(7)
N(1)-Cd(1)-N(4) 105.02(7) N(8)-Cd(2)-O(3) 114.87(7)
N(3)-Cd(1)-N(4) 119.00(7) N(5)-Cd(2)-O(3) 116.20(6)
O(2)-Cd(1)-N(4) 89.31(6)
O(2)-Cd(2)-O(3) 74.27(5)
N(1)-Cd(1)-O(3) 140.17(6) N(8)-Cd(2)-O(1) 84.35(7)
N(3)-Cd(1)-O(3) 79.17(6)
O(2)-Cd(1)-O(3) 72.30(5)
N(5)-Cd(2)-O(1) 79.99(6)
O(2)-Cd(2)-O(1) 67.29(5)
N(4)-Cd(1)-O(3) 102.35(6) O(3)-Cd(2)-O(1) 141.25(5)
N(1)-Cd(1)-N(2) 72.74(6)
N(3)-Cd(1)-N(2) 72.09(6)
N(8)-Cd(2)-O(4) 83.78(7)
N(5)-Cd(2)-O(4) 81.92(6)
O(2)-Cd(1)-N(2) 142.19(6) O(2)-Cd(2)-O(4) 141.04(5)
N(4)-Cd(1)-N(2) 73.91(7) O(3)-Cd(2)-O(4) 66.86(5)
O(3)-Cd(1)-N(2) 143.62(5) O(1)-Cd(2)-O(4) 151.66(5)

Table 4. Photocatalytic activities of cadmium(II) coordination compounds for the degradation of
methylene blue (MB).
Complex
Rate constant Efficiency
Ref.
(min-1)
(%)
37.64
32.60
68.0
[Cd(H4L1)(N3)2]n (1)
[Cd2(L2)(N3)2]·(H2O) (2)
2.63×10-3
2.45×10-3
3.56×10-3
This work
This work
[6a]
[{CdL3(μ-1,1-N3)}2Cd(μ-1,1-N3)2·1.76 CH3OH]n
[Cd2(L4)2(μ-1,3-SCN)2(CH3OH)2]
{[Cd3(pbmb)3(1,3,5-btc)2(H2O)]·3H2O}n
[Cd(pbmb)(1,2,4,5-btec)0.5]n
[Cd2(3-pna)(mip)2(H2O)]·2H2O
[Cd(3-pna)(mip)]2·3H2O
7.01×10-4
64.0
37.0
46.0
48.0
42.0
74.3
86.0
96.5
93.9
78.3
[6b]
-
[21]
-
[21]
-
[22]
-
[22]
[Cd(L5)(dctp)]n
1.10×10-3
1.80×10-3
2.35×10-2
1.69×10-2
9.60×10-3
[23]
{[Cd(L6)(Hbtc)(H2O)]·H2O}n
{[Cd(L7)(1,4-ndc)]n
{[Cd(L8)1.5(bdc-Cl4)]·H2O}n
{[Cd3(μ4-dbba)2(phen)3]·H2O}n
[23]
[24]
[24]
[25]
H4L1=[2-((2-hydroxy-3-methoxybenzylidene)amino)-2-(hydroxymethyl)-propane-1,3-diol];
H2L2 HL3=2-(3-(dimethylamino)
=
bis((3-methoxysalicylidene)ethyl)
ethylamine);
propyliminomethyl) -6- ethoxyphenol; HL4=2-(3-(methylamino) propyliminomethyl)-4,6-
dichlorophenol; L5=1,3-bis(2-methylbenzimidazol-1-ylmethyl)benzene; L6=1,2-bis(imidazol-1-
ylmethyl)benzene; L7=1,4-bis(benzimidazol-1-yl)butane; L8=1,6-bis(benzimidazol-1-yl)hexane;
3-pna=3-pyridylnicotinamide; H2mip=5-methylisophthalic acid; H2dctp=2,5-dichloroterephthalic
acid; H3btc= 1,3,5-benzenetricarboxylic acid; 1,4-H2ndc = 1,4-naphthalenedicarboxylic acid;
H2bdc-Cl4 = 2,3,5,6-tetrachloroterephthalic acid; phen=1,10-phenanthroline; H3dbba=2-(3,5-
dicarboxylatobenzyloxy)benzoic acid; pbmb=1,1′-(1,3-propane)bis-(2-methylbenzimidazole);
1,2,4,5-H4btec=1,2,4,5-benzenetetracarboxylic acid.

Fig. 1. ORTEP drawing (ellipsoid probability at 25%) of complex 1with label scheme of the
crystallographic independent unit. For clarity the -CH2OH groups aredepicted as spheres due to
the positional disorder of these groups.

A
B
Fig. 2. (A) Packing diagram showing interdigitated polymers with indication - interactions in
compound 1 and (B) intra-chain H bonds among the OH groups.

Fig. 3. Molecular structure of complex 2 (ORTEP drawing, ellipsoid probability at 50%) with
atom labelling scheme.

Fig. 4. Perspective view of the complex showing the conformation of the ligand with mean
planes through phenol moieties forming a dihedral angle of 20.12°.
Fig. 5. Crystal packing of 2 showing Cd complexes connected by H-bonds though lattice water
molecules (only hydrogen atoms involved in H-bonds are shown for sake of clarity).

Fig. 6. TGA curve of complex 1 (left) and 2 (right).
Fig.7. Absorption spectra of MB aqueous solution in presence of 1 during irradiation (thespectra
were recorded atintervals of20 minutes).

Fig.8. Absorption spectra of MB aqueous solution in presence of 2 during irradiation (the spectra
were recorded at intervals of 20 minutes).

Fig.9. Plot of photocatalytic degradation kinetics of MB at different concentrations of complexes
1 and 2.

Two cadmium(II)-azido complexes, [Cd(H4L1)(N3)2]n (1) and [Cd2(L2)(N3)2]·(H2O) (2) (H4L1 =
2-((2-hydroxy-3-methoxybenzylidene)amino)-2-(hydroxymethyl)-propane-1,3-diol; and H2L2 =
bis((3-methoxysalicylidene)ethyl)ethylamine) were synthesized and structurally characterized.
Both the complexes are active for photocatalytic degradation of methylene blue (MB) in
presence of UV light.