Unprecedented photosensitivity of heterotrimetallic copper(ii)/sodium/mercury(ii) coordination polymer based thin film semiconductor device

Article abstract of DOI:10.1039/c8nj02261e

A hetero-polynuclear complex, [{CuLNa}₂(μ-_1,1,3-NCS)HgCl(μ-Cl)(μ-_1,3-NCS)]_n {H₂L = N,N′-bis(3-methoxysalicylidene)propane-1,3-diamine}, has been synthesized and characterized. The estimated optical ba

Full text of DOI:10.1039/c8nj02261e

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S. Roy, S. Halder, M. G. B. Drew and P. P. Ray, New J. Chem., 2018, DOI: 10.1039/C8NJ02261E.
Volume 40 Number
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January 2016 Pages 1–846
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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Unprecedented photosensitivity of heterotrimetallic
copper(II)/sodium/mercury(II) coordination polymer based
thin film semiconductor device
a
b
c
b,
Sourav Roy , Soumi Halder , Michael G. B. Drew , Partha Pratim Ray * and Shouvik
a,
Chattopadhyay *
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata - 700032, India.
Tel: +9133-2457-2941; E-mail: shouvik.chem@gmail.com
b
Department of Physics, Jadavpur University, Kolkata 700 032, India.
E-mail: partha@phys.jdvu.ac.in
c
School of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6 6AD,
United Kingdom, E-mail: m.g.b.drew@reading.ac.uk
Abstract: A new trimetallic hetero-polynuclear complex, [{CuLNa} (µ-1,1,3-NCS)HgCl(µ-Cl)(µ-1,3-
2
NCS)] {H L = N,N'-bis(3-methoxysalicylidene)propane-1,3-diamine}, has been synthesized and
n
2
characterized. Estimated optical band gap indicates that the complex belongs to a
semiconductor family. Photosensitivity of the complex is also very high (~57). The complex finds
application in preparing a Schottky barrier diode.
Keywords: Coordination Polymer; Photosensitivity; Schottky diode; SCLC mechanism.

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Introduction
Polymeric structures generated from repeating units of coordination compounds
(usually termed as node or connector) joined through bridging ligands (usually termed as linker
1
or spacer) in any dimensions are known as coordination polymers (CP). These CPs are
extremely important due to their multifunctional uses in non-linear optics, magnetism,
2
separations, extractions, catalysis and selective gas storage etc. Appropriate strategies and
methods are to be applied to construct CPs. The most familiar approach is the node-and-spacer
3
approach, formulated by Robson et al in 1990. Recently, novel hetero-metallic high-
4
dimensionality CPs are gaining tremendous attention for their geometrical flexibility. Use of
trinuclear complexes with compartmental Schiff base ligands as nodes to form CPs are also
5
found in literature.
1
0
d
metal ions are particularly useful for the construction of CPs as these metal ions are
6
flexible in nature and can produce different molecular geometries with severe distortions.
7
Such complexes show interesting photochemical and photophysical properties. These
8
complexes have potential applications in light-emitting diodes and photovoltaic devices.
Mercury(II) complexes, in particular, are used in energy efficient fluorescent light bulbs, paints,
9
paper industry, cosmetics, thermometers and mercury batteries etc. However, its application
9
is limited for its toxicity. As a consequence, CPs of mercury(II) is scarce in the literature
compared to that of zinc(II) and cadmium(II). However, electronic device fabrication using CPs is
the most tempting prospect of these materials which is still in very primary stage. The bridging
organic linkers play the most crucial role in determining their overall electronic and electrical
1
0
properties in CPs. Any coordination compound showing highly influenced rectifying nature

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under incident light radiation can behave as diodes. The non-linear rectifying behaviours of I-V
characteristics of these CP based devices measured under dark and illumination conditions
1
1
prove their Schottky diode characters. Several CPs are reported to harvest visible light and
1
2
trigger photocurrent generation with a quick response to irradiation with visible light.
In the present work, a N O donor Schiff base has been used to prepare a CP containing
2
4
a trimetallic copper(II)/sodium/mercury(II) building block (Scheme 1). The semiconducting
nature of the complex has been determined by estimating its optical band gap using Tauc’s
plot. The semiconducting CP has been found to be photosensitive and a significantly high on-off
ratio is observed when used as a photo-switch. The rectifying nature in I-V characteristics is in
agreement with Schottky diode characteristics of the CP.
Experimental Section
All materials were commercially available, reagent grade and used as purchased from
Sigma-Aldrich without further purification.
Synthesis
Synthesis
of
[{CuLNa} (µ- -NCS)HgCl(µ-Cl)(µ- -NCS)]
n
{H2L
[N,N'-bis(3-
2
1,1,3
1,3
methoxysalicylidene)propane-1,3-diamine]}
A methanol solution (10 mL) of 3-methoxysalicylaldehyde (332 mg, 2 mmol) and 1,3-
diaminopropane (0.13 mL, 1 mmol) was refluxed for ca. 1 h to prepare H L. The ligand was not
2
isolated but used directly for the synthesis of the complex. A methanol (10 mL) solution of
copper(II) chloride dihydrate (170 mg, 1 mmol) was added to the methanol solution (20 mL) of
H2L and the resulting solution was stirred for 15 min. A methanol (10 mL) solution of mercury(II)

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acetate (348 mg, 1 mmol) was then added to it, followed by the addition of a methanol solution
of sodium thiocyanate (81 mg, 1 mmol). The stirring was continued for about 2h. Single crystals,
suitable for X-ray diffraction, were obtained after 3-4 days on slow evaporation of the solution
in open atmosphere.
Yield: 310 mg (50%) [based on copper(II)]. Anal. Calc. for C H Cl Cu HgN Na O S (FW
4
0
40
2
2
6
2 8 2
-
1
=
1241.49): C, 38.70; H, 3.25; N, 6.77; Found: C, 38.4; H, 3.1; N, 6.8%. FT-IR (KBr, cm ): 1614
-
1
-1
5
(
C=N); 2114, 2076 (C≡N). UV-Vis [λmax(nm)] [εmax(Lmol cm )] (Acetonitrile): 233 (1.3×10 ); 279
4
4
2
(
6.6×10 ); 365 (1.7×10 ); 587 (3.1×10 ).
Results and Discussion
Synthesis
The N O donor Schiff base ligand, H L, was prepared by condensing 1,3-
2
4
2
diaminopropane and 3-methoxysalicylaldehyde in 1:2 ratio for 1 h following the literature
1
3
method. The Schiff base ligand (H L) was not isolated and copper(II) chloride dehydrate (1
2
mmol) was added to it with stirring. The solution was stirred for 15 min. Mercury(II) acetate (1
mmol) was then added with constant stirring, followed by the addition of sodium thiocyanate.
The mixture was then kept undisturbed to get crystals of the hetero-polynuclear complex
(Scheme 1).

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Scheme 1: Synthesis of the ligand and the complex.
Description of structure of [{CuLNa} (µ- -NCS)HgCl(µ-Cl)(µ- -NCS)]n
2
1,1,3
1,3
The X-ray crystal structure determination reveals that the complex crystallizes in the
orthorhombic space group Pca2 (bca). Details of the crystallographic data and refinement
1
details have been given in Table 1. Important bond lengths and bond angles have been
gathered in Tables S1 and S2 {Electronic Supplementary Information (ESI)}. The asymmetric unit
of the complex consists of hetero-metallic species [{CuLNa} (µ- -NCS)HgCl(µ-Cl)(µ- -NCS)]. A
2
1,1,3
1,3
perspective view of the asymmetric unit has been shown in Fig. 1.
Table 1: Crystal data and refinement details of the complex.
Formula
Formula Weight
Temperature(K)
Crystal system
Space group
a(Å)
C H Cl Cu HgN Na O S
40 40 2 2 6 2 8 2
1
241.49
50
1
orthorhombic
Pca2 (bca)
1
1
1
2.6601(15)
6.2779(14)
b(Å)
c(Å)
2
2.668(3)
4
Z

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-
3
dcalc(g cm )
1
4
.765
.459
-
1
μ(mm )
F(000)
2
448
Total Reflections
Unique Reflections
Observed data [I > 2 σ (I)]
3
1091
9
088
517
4
No. of parameters
R(int)
5
65
0
.124
R1, wR2 (all data)
R1, wR2 [I > 2 σ (I)]
0
0
.1790, 0.2343
.0843, 0.1930
Each copper(II) has distorted square planar geometry, being coordinated by two
nitrogen atoms [N(19) and N(23) for Cu(1); N(49) and N(53) for Cu(3)], and two phenoxo oxygen
atoms [O(11) and O(31) for Cu(1); O(41) and O(61) for Cu(3)], of the deprotonated Schiff base
2
-
(
L) . The deviations of the coordinating atoms N(19), N(23), O(11) and O(31) from the least-
square mean plane through them are 0.047(15) Å, -0.042(15) Å, -0.049(11) Å and 0.056(11) Å
respectively and that of Cu(1) from the same plane is -0.011(2) Å. Similarly, deviations of the
coordinating atoms [N(49), N(53), O(41) and O(61)] from the least-square mean plane through
them are 0.088(16) Å, -0.089(17) Å, -0.104(10) Å and 0.107(14) Å respectively and that of Cu(3)
from the same plane is -0.003(2) Å. The conformation of the saturated six-membered rings
[
Cu(1)-N(19)-C(20)-C(21)-C(22)-N(23)] and [Cu(3)-N(49)-C(50)-C(51)-C(52)-N(53)] are closer to
14
envelope conformations with the puckering parameters Q=0.49(3) Å, θ=68(2)°, φ=194(3)° and
Q=0.56(3) Å, θ=111(2)°, φ=342(2)° respectively. The N(19)-Cu(1)-N(23) and N(49)-Cu(3)-N(53)
1
5
angles are 95.6(7)° and 97.2(8)° as expected for a typical six-membered chelate. On the other

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hand, both sodium centres are hexacoordinated and have distorted octahedral geometry. Each
sodium ion is surrounded by two phenoxo oxygen atoms, {O(11), O(31) for Na(1) and O(41),
O(61) for Na(2)} and two methoxy oxygen atoms {O(131), O(291) for Na(1) and O(431), O(591)
for Na(2)} of the Schiff base. One nitrogen atom, N(1), of a thiocyanate actually bridges these
two sodium centres. The sixth coordination site of Na(1) is coordinated by a chlorine atom,
Cl(2), whereas the sixth coordination site of Na(2) is coordinated by a nitrogen atom, N(2), from
a symmetry related thiocyanate. The thiocyanate which bridges two sodium centres in end-on
mode also uses its sulphur centre to coordinate a mercury(II) centre, Hg(1). This Hg(1) is
tetrahedral being coordinated by two sulphur atoms, S(1) and S(2) from two thiocyanates and
two chlorine atoms Cl(1) and Cl(2). Cl(2) is unusual in the sense that it actually used as bridging
atom between Na(1) and Hg(1). A unique six-membered [Hg-S-C-N-Na-Cl] ring is produced
which has not been observed in any X-ray characterized structure before the present work. One
of the thiocyanate coordinates a symmetry related (x,-1/2+y,1.5-z) sodium centre to grow the
1
D structure of the complex (Fig. 2).
The distance of Na-O(methoxy) 2.31 Å is larger than that of Na-O(phenolate) 2.48 Å.
Intra-molecular Cu(1)⋯Na(1) and Cu(3)⋯Na(2) distances are 3.42(8) Å and 3.44(9) Å
respectively. The bridging angles Cu(1)-O(11)-Na(1), Cu(1)-O(31)-Na(1), Cu(3)-O(41)-Na(2) and
Cu(3)-O(61)-Na(2) are 107.1(6)°, 107.3(6)°, 106.6(5)° and 108.3(6)°, respectively. The Cu(1)-
O(11)-O(31)-Na(1) and Cu(3)-O(41)-O(61)-Na(2) cores are almost planar, dihedral angles
between the O(11)Cu(1)O(31) and O(11)Na(1)O(31) planes is 1.47° and that between
O(41)Cu(3)O(61) and O(41)Na(2)O(61) planes is 1.77°.

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Fig. 1: Perspective view of the asymmetric unit of the complex with selective atom numbering
scheme. Hydrogen atoms have been omitted for clarity.
Fig. 2: Perspective view of the polymeric structure of the complex. Hydrogen atoms have been
omitted for clarity.

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Supramolecular Interaction
The complex shows one C-H∙∙∙π interaction. The hydrogen atom, H(14), attached to
carbon atom, C(14), is involved in an inter-molecular C-H∙∙∙π interaction with a symmetry
related (x,-1/2+y,3/2-z) phenyl ring [C(55)-C(56)-C(57)-C(58)-C(59)-C(60)] as shown in Fig. 3. The
details of the geometric features of the C-H∙∙∙π interactions have been given in Table 2.
Table 2: Geometric features (distances in Å and angles in°) of the C-H∙∙∙π interactions obtained
for the complex.
C-H···Cg(Ring)
H···Cg
C–H···Cg (°)
C···Cg (Å)
a
C(14)-H(14)∙∙∙Cg(11)
2.83
138
3.570(18)
a
Symmetry transformations: = x,-1/2+y,3/2-z. Cg(11) = Centre of gravity of the ring [C(55)-
C(56)-C(57)-C(58)-C(59)-C(60)] for the complex.
Fig. 3: Perspective view of inter-molecular C-H∙∙∙π interaction formed in the complex with
selective atom numbering scheme. Only relevant atoms have been shown in the figure.

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Both copper(II) centres [Cu(1) and Cu(3)] in the complex are involved in cation∙∙∙π
interactions. The copper(II) centre, Cu(3), is involved in two cation∙∙∙π interaction, one with a
phenyl ring [C(12)-C(13)-C(14)-C(15)-C(16)-C(17)] and the other one with a symmetry (1-
x,y,1/2+z) related phenyl ring [C(25)-C(26)-C(27)-C(28)-C(29)-C(30)]. Similarly Cu(1), is involved
in two cation∙∙∙π interactions, one with a symmetry (1-x,y,-1/2+z) related phenyl ring [C(42)-
C(43)-C(44)-C(45)-C(46)-C(47)] and the other one with a phenyl ring, [C(55)-C(56)-C(57)-C(58)-
C(59)-C(60)]. As a result of these interactions, a 2D structure is formed, as shown in Fig. 4.
Details of the geometric features of cation∙∙∙π interactions have been given in Table 3.
Fig. 4: Perspective view of 2D structure formed by cation∙∙∙π interactions in the complex.
Hydrogen atoms have been omitted for clarity.

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Table 3: Geometric parameters (Å,°) for the cation∙∙∙π interactions for the complex.
Cg(Ring I)···M Cg(I)···M (Å)
β (°)
M···Prep (Å)
Cg(8)∙∙∙Cu(3)
3.612
3.929
3.548
16.38
3.466
a
Cg(9)∙∙∙Cu(3)
Cg(10)∙∙∙Cu(1)
27.05
22.89
14.35
-3.499
3.269
-3.307
b
Cg(11)∙∙∙Cu(1)
3.414
a
b
Symmetry transformations: = 1-x,y,1/2+z; = 1-x,y,-1/2+z.
β = Cg(I)∙∙∙M vector and normal plane of ring(I); M∙∙∙Prep = Perpendicular distance of M(metal)
on ring (I); Cg(8) = Centre of gravity of the ring [C(12)-C(13)-C(14)-C(15)-C(16)-C(17)], Cg(9) =
Centre of gravity of the ring [C(25)-C(26)-C(27)-C(28)-C(29)-C(30)], Cg(10) = Centre of gravity of
the ring [C(42)-C(43)-C(44)-C(45)-C(46)-C(47)], Cg(11) = Centre of gravity of the ring [C(55)-C(56)-
C(57)-C(58)-C(59)-C(60)], for the complex.
Morphological Analysis
Fig. 5: FESEM image of the complex.

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The morphological study of the complex shows that the material has feather like
morphology, as shown in Fig. 5.
Optical Analysis
In this study, the UV-Vis absorption spectrum of the complex (Fig. 6) has been recorded
for the deposited thin films of the complex preparing a well dispersion in acetonitrile, in the
range 200-1000 nm. The absorption spectrum of the complex depicts strong energy absorption
in the visible region at ~365 nm. Optical band gap has been calculated by using Tauc’s equation
1
6
(Eqn. 1).
…
…(1)
Where ꢀ is the absorption coefficient, γ is the frequency of light, h is the Plank’s
constant, A is a constant taken as 1, E is the band gap energy, n is the nature of transition
g
(taken as ½ for direct and 2 for indirect transition).
The direct energy band gap (E ) can be determined by extrapolating the linear region of
g
2
the plot (αhγ) versus hγ to α=0 absorption and the value has been estimated to be about 3.01
eV (Fig. 7).

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Fig. 6: UV-Vis absorption spectrum of the complex. (Inset shows absorption profile within 500-
00 nm).
9
Fig. 7: Tauc’s plot for the complex.

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Estimated optical band gap energy suggests that the complex belongs to semiconductor
family. With this result the electrical transport properties of the complex has been further
analyzed in detail and the possibility of technologically challenging application in thin film active
devices has been investigated. To try with, the complex has been applied in a Schottky device.
Electrical Characterisation
The current voltage (I-V) measurements have been done in dark and under AM1.5G light
illumination (Fig. 8). The graph shows a rectifying nature which depicts its Schottky behaviour
having a rectification ratio of 26.09 which is significant.
Fig. 8: Current-Voltage characteristics curve in dark and under light.
The graph also suggests that there is a large difference between dark and photo current.
So the dark and photoconductivity of the material have been estimated. The dark and

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-
6
-1
-5
-1
photoconductivity are estimated as 1.48x10 Sm and 8.40x10 Sm respectively.
Subsequently the photosensitivity (photoconductivity/ dark conductivity) of this material is
17
about 57. This has been unprecedented compared to the other materials of this type.
Examples of similar complexes and their corresponding photosensitivities are gathered in Table
1
8
4
. The large photosensivity with the successful application of the material in Schottky device
suggests that this material can be a potential candidate for the application in photovoltaic
devices.
Table 4: Previously reported X-ray characterized photosensitive complexes.
Complex
Conductivity Conductivity Photosensitivity
Ref
in dark
under light
1
-8
-8
[
CdL (µ- -SCN) ]
1.01x10
2.16x10
14.36
1.83
17
1
,3
2 n
-
-
-
-
4
4
4
4
-4
[
Cu (adc)(4-
8.21×10
11.84×10
18a
2
pic) (H O) ][ClO ]
4 2
6
2
4
-4
{
[Zn(adc)(4-
spy) (H O) ]}
2 n
5.12×10
6.54×10
6.60×10
16.48×10
1.96-2
3.5
18b
18b
18c
2
2
-4
{
[Cd(adc)(4-spy)2-
28.77×10
(
H O) ]}
2
2 n
-4
[
Cd(2,2’-dsb)(4-
10.71×10
0.54
nvp)(DMF)(H O)]
2

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1
-5
6
-5
[
Cu (L ) (μ- -SCN) ]
2 n
3.63 x 10
4.13 x 10
2.83
57
18d
2
2
1,3
-
-5
[
{CuLNa} (µ-1,1,3-
1.48x10
8.40x10
This work
2
NCS)HgCl (µ- -NCS)]
2
1,3
n
1
Where,
HL
=
2-(2-(ethylamino)ethyliminomethyl)-6-ethoxyphenol;
H2adc
=
acetylenedicarboxylic acid; 4-pic = 4-picolene; 4-spy = 4-styrylpyridine; H 2,2’-dsb = 2,2’-
2
disulfanediyldibenzoic acid (2,2’-dsba) and 4-nvp = 4-(1-naphthylvinyl)pyridine.
Further analysis of the charge transport mechanism has been done by thermionic
emission theory given by the following equations:
Here I is the forward current, I is the reverse saturation current, V is the applied bias
o
voltage, q is the electronic charge, k is the Boltzmann constant, and T is the absolute
temperature, n is the ideality factor. I is given by:
o
-2
2
*
A is the effective diode area taken as 7.065 x 10 cm , A is the Richardson constant given by 32
-
2
-1
AK cm , Ø is the Schottky barrier height.
B
19
The various Schottky parameters are estimated using Cheung’s equations :

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dV
η
kT
q
=
(
) + IRS
d ln I
η
kT
I
H (I) =V −
ln(
)
2
*
q
AA T
H(I) = IR +ηφB
S
Where R is the series resistance and other notations remain same.
s
The ideality factor has been estimated from the intercept of the dV/dlnI vs. I plot has
been given in Fig. 9. Further, the barrier potential height and the series resistance has been
evaluated from the intercept and slope of H(I) vs. I plot, as shown in Fig. 10. The various
parameters calculated have been enlisted in Table 5.
Fig. 9: dV/dLnI vs. Current plot in dark and light conditions.

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Fig. 10: H vs Current graph in dark and light conditions.
The deviation of the ideality factor from 1 may be attributed to the presence of
2
0
inhomogeneities of the Schottky barrier height and the existence of series resistance. To get a
better understanding of the carrier transport mechanism through the metal semiconductor
contact, the forward I-V curve has been analysed. Mobility, lifetime, carrier concentration and
diffusion length have been evaluated by SCLC theory. The log I vs. log V (Fig. 12) graph clearly
shows three distinct regions with different slopes. At lower bias, represented by region I, the
material follows ohmic nature with current directly proportional to voltage. Here the current is
contributed by bulk generated electrons of the film, rather than the injected free carriers. The I-
21
V curve indicates tunnelling as the main contributing factor. The characteristics curve in
region II is dominated by SCLC, where current is directly proportional to square of voltage (Fig.
2
1
1). Effective carrier mobility has been estimated from I vs. V graph (Fig. 11) using the Mott-
2
2
Gurney equation :
2
9
ꢀ ε ε AV
eff
0 r
I =
3
8
d

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Where I is the current, ℰ is the permittivity of free space, ℰ is the dielectric constant,
0
r
ꢀeff is the effective electron mobility calculated above and d is the thickness of the film (taken
as 1 ꢀm in this case).
Further the carrier concentration, lifetime and diffusion length is estimated using the
2
3
following set of equations :
σ
ꢀeff
N =
q
9
ε0εr
V
τ
=
( )
8
d
I
LD = 2D
τ
The ability of the synthesized material to be used for device application can be
determined from the value of diffusion length. The diffusion coefficient (D) (Table 5) has also
24
been calculated employing the Einstein Smoluchowski equation :
qD
ꢀeff
=
kT
2
Fig. 11: I vs V graph in dark and illumination conditions.

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Fig. 12: Log I vs Log V graph in dark and illumination conditions.
Dielectric Measurements
Impedance spectroscopy has been widely used to study the charge transport behaviour
of nanoparticles. The detailed analysis of the transport property of the prepared sample has
been done and the impedance parameters of the material have been measured. The complex
plane impedance plot i.e. Nyquist plot of the sample has been shown in Fig. 13. The plot shows
a semicircle where the bulk resistance of the synthesised material is evaluated to be 640.62 KΩ
from the diameter of the arc.
Fig. 13: Nyquist plot for the complex.

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The Bode plot of the material (Fig. 14) has been done and the electron lifetime of the
material has been calculated. The peak frequency is related to the inverse of the recombination
lifetime or electron lifetime. Electron lifetime has been determined from the following
2
5
equations:
Here f denotes the peak frequency. The electron lifetime has been calculated and found to be
m
-5
3
.76 x 10 sec.
5
-
-
-
-
-
-
-
3.5x10
5
3.0x10
5
2.5x10
5
2.0x10
5
1.5x10
5
1.0x10
4
5.0x10
.0
0
1
0
2
10
3
10
4
10
5
10
6
10
7
10
8
10
1
Log Frequency (Hz)
Fig. 14: Bode plot for the complex.
The relative dielectric constant has been measured on a pellet. The complex has been
pelletized into a disc having diameter of 7.32 mm and thickness of 1.8 mm. The variation of the
capacitance (C) as a function of the frequency (f) at constant bias potential has been shown in
Fig. 15. The room temperature capacitance of the complex is shown to be frequency dependent
at relatively lower frequencies. The capacitance decreases with increasing of frequency and

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-
10
becomes saturated at higher frequency (Fig. 15). The capacitance at saturation is 6.599 x 10
F. From the saturation level the relative permittivity of the complex has been calculated
2
6
employing following equation:
Where, is the permittivity of free space, is the relative permittivity of the complex,
is the capacitance (at saturation) and and is the thickness and effective area of the pellet.
Using the above formula the relative dielectric constant ( ) of the complex has been estimated
to be 10.53.
Fig. 15: Capacitance vs. Frequency plot

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Table 5: Charge conducting and Schottky device parameters of the complex based thin film
device.
Conditions On
Off
ratio
21.66 1.48x 0.35
σ
RS(KΩ)
ΦB
SCLC
μeff
N
τ
D
LD
(
sec)
-
1
1
1
2
/
Sm
I.F
dV/d H(I)
LnI
(eV)
σ
(mV sec )
(m / (m)
sec)
-
1
Sm
-
6
-7
DARK
3.24 2.67 0.71
1.78 1.64 0.62
3.75x10 4.57x10
4.11x 0.13 2.34 4.04x
-
6
-9
-5
1
0
5
x10
10
1
8
1
0
-
4
-6
LIGHT
30.75 8.40x 0.58
1.98x10 3.57x10
2.58x 0.07 7.83 1.08x
-
5
-8
-4
1
0
4
x10
10
1
8
1
0
IR, UV-Vis and photophysical study
Distinct band due to the azomethine (C=N) group at 1614 cm has been routinely
-
1
2
7
-1
noticed in the IR spectrum of the complex. There are two strong bands at 2076 and 2114 cm ,
indicating the presence of terminal (N-bonded) and end-to-end bridged thiocyanate
28
respectively, which are also evident from the crystal structure determination. Band at 2929
-
1
29
cm has been observed due to alkyl C-H bond stretching.
Electronic spectrum of the complex displays five bands around 233 nm, 279 nm, 365 nm
and 587 nm. The complex exhibits fluorescence. Mean lifetimes (гavg) of the exited states is 3.1
ns. Decay profile (Fig. S1) and the photo-physical data (Table S3) have been given in Electronic
Supplementary Information (ESI)}.

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PXRD
Experimental XRD pattern of the bulk product is in excellent harmony with the
simulated XRD pattern generated from single crystal X-ray diffraction data (CIF) using the CCDC
Mercury software. This indicates consistency of the bulk sample (Fig. 16).
Fig. 16: Experimental and simulated PXRD patterns of the complex confirming purity
of the bulk material.
Hirshfeld surfaces
Hirshfeld surfaces of the complex, mapped over dnorm, shape index and curvedness, have
been shown in Fig. 17. Red spots on the dnorm surface (Fig. 17) indicate the interaction between
chlorine and hydrogen atoms. S∙∙∙H, O∙∙∙H and N∙∙∙H contacts have also observed in the Hirshfeld
surfaces as smaller visible spots of light colour. The intermolecular interactions appearing as
distinct spikes in the 2D fingerprint plot have been shown in Fig. 18.

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Fig. 17: Hirshfeld surfaces mapped with dnorm (left), shape index (middle) and curvedness (right)
for the complex.
Fig. 18: Fingerprint plots: Broken down into contributions from specific pair of atom types.
Mass Spectra
Mass spectrum (Fig. 19) of the complex has been recorded in acetonitrile at room
temperature. In the mass spectrum of the complex, peaks at m/z: 403.97, 425.85, 828.95 have
+
been observed. Peaks at m/z values 403.97, 425.85 and 828.95 can be assigned as [CuLH] ,
+
+
[
CuLNa] and [CuLNaClHg(NCS)K(H O) (CH OH)H] respectively.
2 2 3

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Fig. 19: Mass spectrum of the complex.
Concluding Remarks
In summary, a trimetallic copper(II)/sodium/mercury(II) coordination polymer has been
synthesized. The estimated optical band gap energy is 3.01 eV, which suggests that the complex
belongs to semiconductor family. The high value (~57) of photosensitivity is rare for this kind of
complexes. The nature of the I-V curve indicates that the complex based device behaves as
Schottky barrier diode.

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Acknowledgements
S.R. thanks UGC for providing fellowship. S.C. wishes to thank the UGC-CAS II programme,
Department of Chemistry, Jadavpur University, for financial support under the head
[
Chemicals/Consumables/ Glassware].
Notes and references
Electronic supplementary information (ESI) available: Experimental details, Table S1-S3 and Fig.
S1. CCDC 1827627 contains the supplementary crystallographic data for the complex.
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