Synthesis, X-ray crystal structure, photo luminescent property, antimicrobial activities and DFT computational study of Zn(II) coordination polymer derived from multisite N,O donor Schiff base ligand (H2L1)

Article abstract of DOI:10.1016/j.molstruc.2017.03.017

A unique thiocyanato linked 1D chain of Zn(II) coordination polymer [Zn₂L¹(μ_1,3-SCN)(η¹SCN)]_n (1) has been synthesized using potential multisite compartmental N,O donor Schiff base blocker ligand (L

Full text of DOI:10.1016/j.molstruc.2017.03.017

Accepted Manuscript
Synthesis, X-ray crystal structure, photo luminescent property, antimicrobial activities
and DFT computational study of Zn(II) coordination polymer derived from multisite
1
N,O donor Schiff base ligand (H L )
2
Dhrubajyoti Majumdar, M.S. Surendra Babu, Sourav Das, Jayanta Kumar Biswas,
Monojit Mondal, Suman Hazra
PII:
S0022-2860(17)30278-8
10.1016/j.molstruc.2017.03.017
MOLSTR 23513
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 17 December 2016
Revised Date: 3 March 2017
Accepted Date: 4 March 2017
Please cite this article as: D. Majumdar, M.S. Surendra Babu, S. Das, J.K. Biswas, M. Mondal, S.
Hazra, Synthesis, X-ray crystal structure, photo luminescent property, antimicrobial activities and DFT
computational study of Zn(II) coordination polymer derived from multisite N,O donor Schiff base ligand
1
(H L ), Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.03.017.
2
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GRAPHICAL ABSTRACT

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Synthesis, X-ray crystal structure, photo luminescent property, antimicrobial activities and
DFT computational study of Zn(II) coordination polymer derived from multisite N,O
donor Schiff base ligand (H2L1)
Dhrubajyoti Majumdara*, M.S. Surendra Babub, Sourav Dasc*, Jayanta Kumar Biswasd Monojit
Mondald, Suman Hazrae,
aDepartment of Chemistry; Tamralipta Mahavidyalaya, Tamluk-721636, West Bengal, India
bDepartment of Chemistry, GITAM University, Hyderabad Campus, Hyderabab-502329, India
cDepartment of Chemistry; Institute of Infrastructure Technology Research and Management;
Near Khokhara Circle, Maninagar East, Ahmedabad-380026, Gujarat, India
dDepartment of Ecological Studies, University of Kalyani, Kalyani-741235 , West Bengal, India
eKarak S.S. High School, Tamluk, West Bengal-721632, India
E-MAIL: dmajumdar30@gmail.com

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Abstract
A unique thiocyanato linked 1D chain of Zn(II) coordination polymer [Zn2L1(µ1,3-
SCN)(η1SCN)]n (1) has been synthesized using potential multisite compartmental N,O donor
Schiff base blocker ligand (L1H2) in presence of Zn(OAc)2 and KSCN. The Schiff base ligand
[N, N’-bis(3-methoxysalicylidenimino)-1,3-daminopropane]
(L1H2) is 2:1 molar ratio
condensation product of O-vaniline and 1,3-diaminopropane in methanol medium. The
characterization of Complex 1 was accomplished by means of different micro analytical
techniques like elemental analyses, IR, UV-Vis, 1H NMR, emission spectroscopy and Single X-
ray crystallographic study. Complex 1 crystallizes in Orthorhombic system, space group Pbca,
with values a = 11.579(2), b = 18.538(3), and c = 22.160(4) Å; α = β = γ = 90.000; V =
4756.6(14) and Z = 8. The single crystal X- ray revealed that the one dimensional chain system
with the repeating unit [Zn2(ꢀ1,3-SCN)(η1SCN)(L1)]n bridge by a end to end ꢀ1,3
thiocyanate anion. Within each repeating unit two different types of Zn(II) ions are present. One
of these is five-coordinate in a square pyramidal geometry while the other is six-coordinate in an
octahedral geometry. A brief but lucid comparative approach has been demonstrated in between
Schiff base (L1H2) and complex 1 with respect to their photoluminescence activities. Active
luminescence behavior of complex 1 in presence of ligand (L1H2) is due to quenching of PET
process which is mediated by ‘chelating effect’. Complex 1 exhibits strong antimicrobial
efficacy against some important Gram +ve and Gram -ve bacteria. Apart from antimicrobial
potential, a combined experimental and theoretical investigation has been performed via DFT on
molecular structure of complex 1 with respect to Hirshfeld surface analysis.
Key words: Zn(II) coordination polymer, X-ray crystal structure, Photoluminescence behavior,
antimicrobial activity, DFT study.

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1. Introduction
The design and novel synthesis of coordination polymer (CP) and molecular framework of
Group 12 metal ions (Zn, Cd and Hg) in presence of polydentate Schiff base ligand [1-6] and
inclusion of a suitable linker like [SCN]-, [N3]-, [OCN]- & [N(CN)2]- have achieved an immense
progress of research in the field of synthetic inorganic chemistry. Thus metal-organic
coordination polymers (MOCPS) having 1-, 2- or 3-D structures are properly assembled with
particular specific metal ions like Zn(II) or Cd(II). Hence current research has expanded in the
fields of supramolecular chemistry and crystal engineering [7,8] because of their intriguing
structural motifs and functional behaviors [9-13]. Among Group 12 metal ions, only Zn is a
unique transition metal, playing important roles in different fields of Chemistry viz. enzyme
catalysis [14], apoptosis [15], neurotransmission [16], luminescence, nonlinear optics, molecular
sensing [17-21], biological modeling of metalloenzymes [22,23]. Since Zn(II) has no
spectroscopic signature as well as d10 filled shell configuration, ligand field stabilization energy
(LFSE) is always zero, hence the present situation permits Zn(II) with a wide range of
symmetries and various coordination number fulfillment. The aforesaid conditions are
considered as requisite "key criteria" for designing metal-organic coordination polymers
(MOCPS). Novel pioneer Prof. Sir Hugo Schiff opened up a beautiful research gate after his
novel discovery of Schiff base [24]. In the current research scenario, organic or inorganic
luminescent compounds like Schiff base ligands offer a wide array of applications including
emitting materials for organic light emitting diodes, photo catalysis agents and fluorescent
sensors for inorganic analyses. The group 12 metal ions exhibit enhanced luminescence property
owing to ligand chelation or coordination with proper donor centers [25, 26]. Thus most of the
researchers find a strong intriguing relationship between Group 12 metal ions and their

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synthesized Schiff base in presence of suitable linker pseudo halide ions [SCN]- that it develops
a totally new coordination polymer which can function as fluorescent sensors. For Zn(II)
coordination polymer, the complex molecules are clipped into a very special restricted MOF
work, and due to this reason we expected to gain extra conformational rigidity that helpful for
strong fluorescence intensity behavior of the complex. In the present study, we have used pseudo
halide [SCN]- as co-ligand which can bind with the Zn(II) ions as terminal ligand and as well
as end to end bridge fashion. The studies have shown that the thiocyanate anion ligand has
several different coordination modes as depicted in Scheme 1[A-E]. For bi and polynuclear
complexes,,most important binding modes are identified as µ1,1-NCS, µ1,1-SCN, µ1,3-NCS, µ1,1,3
-
SCN and µ1,1,1,3-SCN [27-33]. Additionally µ1,3-SCN exhibits strong interaction with proper
metal ions to form extended 2D, 3D , 1D network polymers in presence of suitable Schiff base
ligand [34,35].
In this study, pendant [
SCN]- ligand links two dinuclear units to each other through an end to end
bridging fashion to accomplish the formation of 1D chain coordination polymer. This work
lucidly communicated the successful synthetic details of complex 1, spectral characterizations
1
like IR, UV-vis, H NMR, emission spectra and Single X-ray crystal structure analysis. The
photoluminescence study reveals that complex 1 is strongly luminescence active with respect to
free Schiff base ligand (H2L1). Accordingly, we report the first comprehensive studies involving
synthesis, structure, photophysical property, antimicrobial activity, Hirshfeld surface analysis
and DFT on a family of 1D chain of Zn(II) coordination polymer.

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N
S
C
N
C
S
N
C
S
M
M
M
M
M
M
ꢀ1,3ꢁNCS
C
ꢀ1,1ꢁSCN
B
ꢀ1,1ꢁNCS
A
M
N
C
S
M
M
N
C
S
M
M
M
M
ꢀ1,1,3ꢁSCN
D
ꢀ1,1,1,1,3ꢁSCN
E
Scheme 1. Different Bridging Modes of the Thiocyanate anion.
2. Experimental
2.1 Materials
All chemicals which are used in the current research work must be reagent grade and used as
received without further purification. All solvents like methanol, ethanol and other reagents used
in this work were obtained from commercial sources. O-vaniline and 1,3-diaminopropane were
purchased from Sigma Aldrich Company, USA. Zinc acetate dehydrate was purchased from
Merck chemical Company. KSCN was purchased from SDFCL, India. All synthetic research
reactions and work-up were done in open atmospheric condition.

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2.2 Physical measurement
Elemental analyses (carbon, hydrogen and nitrogen) of both Schiff base ligand and complex 1
were determined with a Perkin–Elmer CHN analyzer 2400. FT IR spectra were recorded as KBr
pellet in the range 4000–400 cm-1 with 16 scans at a wave number resolution of 4 cm-1 on a
Perkin–Elmer spectrum RX 1 and FT IR detector used as DTGS (Deuterated triglycine sulphate).
The UV-Vis spectra of complex 1 and ligand were recorded using DMSO solvent on a Hitachi
1
model U-3501 Spectrophotometer. The H NMR spectra of novel Schiff base were recorded on
Bruker 300MHz FT-NMR spectrophotometer using trimethylsilane as internal standard in CDCl3
solvent. All spectra were corrected for the instrumental functions. Perkin-Elmer LS50B
Spectrofluorimeter model was used for the fluorescence measurements of Zn(II) coordination
polymer and Schiff base ligand (H2L1) at room temperature (298K). The solutions of Schiff base
ligand (H2L1) and complex 1 were prepared in DMSO solvent. The fluorescence quantum yield
(Φ) has been determined using quinine sulfate as the secondary standard (Φ = 0.57 in water) [36]
by employing the following equation:
ΦS AS (Abs)R nS2
=
×
×
----------------------------(1)
ΦR AR (Abs)S nR2
Here, A terms denote the fluorescence area under the curve; Abs denotes absorbance; n is the
refractive index of the medium; is the fluorescence quantum yield; and subscripts S and R
Φ
denote parameters for the studied sample and reference, respectively.
2.3 Antimicrobial assay
Four Gram negative bacterial strains (Escherichia coli K12, Salmonella enterica ser. typhi SRC,
Proteus vulgaris OX19 and Enterobacter aerogenes 10102) and one Gram positive bacterial

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strain (Bacillus subtilis 6633) were selected for in vitro assessment of antibacterial properties of
complex
Gene Bank (MTCC), Institute of Microbial Technology, Chandigarh, India and Department of
Microbiology, University of Kalyani, West Bengal, India. Primarily complex was dissolved in
dimethyl sulfoxide (DMSO) for antimicrobial assay while using amoxicillin, a clinically
recommended antimicrobial agent as a reference [37]. Different concentrations of complex
1. The bacterial strains were procured from Microbial Type Culture Collection and
1
1
were prepared in sterilized Luria-Bertani medium (Modified) and 1% over night bacterial culture
was inoculated to the respective medium maintaining the final concentration of DMSO always
within 1%. The media were incubated at 37°C for 24 hours. Individual bacterial growth was
measured by UV-VIS spectrophotometer at 600nm and minimum inhibitory concentrations
(MIC) of the complexes against the tested strains were determined as per NCCLS protocol [38].
Susceptibility of those bacterial strains to complex
1 was analyzed by agar well diffusion method
and antibacterial potential was assessed on the basis of the growth inhibition zone diameter
measurement (mm) [39]. Bacterial growth kinetics analyses were studied for four bacterial
strains (Bacillus subtilis 6633, Enterobacter aerogenes 10102, Proteus vulgaris OX19 and
Salmonella enterica ser. typhi SRC) subjected to complex 1.
3. Synthesis
3.1 Synthesis of Schiff base (H2L1)
Compartmental Schiff base ligand (L1H2) is actually the condensation product of O-vaniline and
1,3-diaminopropane in a 2:1 molar ratio (Scheme 2). It was synthesized and characterized using
standard method [40]. Yield: (90%), Anal. Calc. for C19H22N2O4: C, 66.65; H, 6.48; N, 8.18
Found: C, 66.71; H, 6.42; N, 8.08%. IR (KBr, νmax/cm-1):
ν
(C=N) 1641, ν(C-Ophenolic) 1254, ν(O-

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1
H) 3449, UV-vis (λmax/ nm): 258, 398 nm. H NMR for (H2L1
)
(δ
, 300MHz): 2.11(t, J=6.45,
2H8), 3.74 (t, J=8.1, 2H7), 3.91 (s, 3H1), 6.79-6.95(m, 1H2, 1H3, 1H4), 8.37 (s, 1H5), 10.26 (s,
1H6), ppm.
Scheme 2: Synthesis of Schiff base ligand (H2L1).
3.2 Synthesis of complex 1
Light yellow colored crystals of complex
1 was synthesized by one pot reaction after reacting
Zn(II) acetatate dihydrate (0.21949g, 1mmol) and Schiff base (L1H2
)
(0.342g, 1mmol) in
presence of KSCN in methanol solvent medium after constant stirring for 2.5 hrs. The light
yellow colored solution was additionally refluxed for 15 min at 700C and the resulting filtrate
was kept in a refrigerator for crystallization by slow evaporation. After 5 days light yellow
colored plate-shaped single crystal suitable for X-ray crystallography was obtained. Yellow
crystal was isolated by filtration and air dried (Yield: 0.325 g: 60%). Anal. Calcd. for
C21H20Zn2N4O4S2: C, 42.91; H, 3.40; N, 9.52. Found: C, 42.92; H, 3.40; N, 9.50 %. IR (KBr
pellet, cm-1):
ν(C≡N) 1627, ν(C-Ophenolic) 1251-1249, ν(Zn-N) 454 , νSCN 2146-2086, ν(O-
H)3467-2936 , λmax(CH3OH) 230.5, 269.2 & 354 nm.

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3.3. X-ray crystallographic study
Diffraction quality single crystal data of Zn(II) coordination polymer was collected at 293(2) K.
Data collections were made using a AXS SMART APEX-II CCD area detector equipped with a
graphite monochromatic MO-Kα radiation (K = 0.71073Å) source in the
ω scan mode at 293(2)
K. The molecular structure of complex
1 has been solved by direct methods and refinement by
full-matrix least squares on F2 using the SHELXS-2014 package [41, 42]. Non-hydrogens atoms
in complex
fixed at calculated positions, and their positions were refined by a riding model. Absorption
correction were applied to the collected data of reference complex using the program SADABS
1 crystal were refined with anisotropic thermal parameters. Hydrogen atoms were
1
[43,44]. For Crystal structure refinement purpose we have used different programs like
SHELXS-2014, ORTEP-3, DIAMOND-3.1v [45] and MERCURY-3.8. Different
crystallographic figures were generated using Diamond-4.2 software. A summary of the
crystallographic data and structure refinement parameters of complex
1 is given in Table 1.
Crystallographic data (excluding structure factors) for the structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos.
CCDC 1501365. Copies of the data can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, U.K.: http://www.ccdc.cam.ac.uk/cgi-bin/catreq.cgi, e-mail:
data request@ccdc.cam.ac.uk or fax: +44 1223 336033.

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Table1 Crystal Data and Structure Refinement Parameters of Complex
1
Formula
M/g
C21H20N4O4S2Zn2
587.27
Crystal system
Space group
a/Å
orthorhombic
P b c a
11.579(2)
18.538(3)
22.160(4)
90.00
b/Å
c/Å
β
(°)
V/Å3
Z
4756.6(14)
8
ρc/g cm-3
1.640
ꢀ
/mm-1
2.228
F(000)
2384
Cryst size (mm3)
0.042 × 0.028 × 0.014
θ
range (deg)
25.242 to 26.594
Limiting indices
-14
-23
-22≤ l
≤
≤
h
k
≤ 14
≤ 23
≤ 27
Reflns collected
Ind reflns
57230
4918 [Rint = 0.0445, Rsigma
=
0.0230]
Completeness to θ (%)
99
Refinement method
Full-matrix-block least-squares on
F2
Data/restraints/
parameters
4918/0/300
Goodness-of-fit on F2
Final R indices
1.128
R1 = 0.0368
[I > 2
θ
(I)]
wR2 = 0.0872
R indices (all data)
R1 = 0.0606
wR2 = 0.1058
0.661 and -0.339
Largest diff. peak and
hole(e ·Å-3)

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3.4 X-ray crystal structure of complex 1
Single crystal x-ray diffraction was used unambiguously to establish the identifiable structure of
complex 1. The perspective view of complex with numbering scheme is depicted in Figure 1a.
The single X-ray crystallographic analysis of complex reveals that it crystallizes in
orthorhombic system with space group Pbca. Selected bond parameters of are summarized in
the Table S1 (See Supplementary material)
1
1
1
.
The asymmetric unit of
by the coordination action of one fully deprotonated equatorial [L1]2- and two axial [SCN]-
, H2L1 acts as a hexadentate (N2O4) dianionic ligand [L1]2- . Two unidentate
1 (Fig. 1b) consists of dinuclear moieties which are assembled together
ligands. In complex
1
imine N atoms bind Zn1 centre, two unidentate oxygen atoms of methoxy groups coordinate
with Zn2 centre, two bridging deprotonated phenoxide O atoms bride between two Zn(II) ions
(Zn1 and Zn2) into a dinuclear unit . In each dinuclear unit, Zn2 atom unites to its neighboring
unit by means of one end-to-end (EE ꢀ
-1,3) [SCN]- coligands to Zn1 centers forming a one
dimensional zigzag chain polymeric chain running along the b-axis (Fig 2).
The stereochemistry at Zn1 centers can be described as a distorted square pyramidal with two
phenoxido O, two imine N atoms in equatorial plane and one thiocyanato S atom in the the axial
plane. In addition, geometry distortion information can be obtained from structural index or
Addison parameter tau (
structures (for square pyramid,
the two largest angles around the central metal) [46].The Addison parameter
ґ
) which represents the relative amount of distortion in the crystal
= 0; trigonal bipyramid, =1; = ( )/60º, where and are
=0.133 of Zn1
ґ
ґ
ґ
α
-
β
α
β
ґ
center is also supportive for distorted square pyramidal geometry (Fig 3a). Here it is important to
mention that in order to satisfy the charge and coordination requirements, apart from the bridging

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thiocyanate anion another thiocyanate anion coordinate the Zn2 through its N-coordinating site
in a momodentate fashion generating ZnO4N2 coordinating environment in a distorted octahedral
geometry where two oxygen atoms are coming from phenolate oxygen and other two are from
oxygen atoms are from methoxy groups (Fig 3b).
Here, we would like to add further details on the molecular structure of complex
1 as follows:
[SCN]- is an active potential ambidentate ligand which prefers to bind with Zn2 centre through
electronegative hard centre (N-donation). On the other hand, Zn1 center has shown affinity for
relatively softer S-coordination of [SCN]- ions. The coordination preference of different binding
atoms towards metal can be explained in terms of symbiosis concept. The Zn2 center are
relatively harder compared to Zn1 as former is attached to four oxygen atoms. So, hard centre
dontion i.e. N-donation of [SCN]- ion is preferable towards Zn2. Complex
1 displays strong
intramolecular C-H…….S [3.848 (Å)] interactions which also propagates along b-axis where
two neighboring dinuclear subunits are interacting with each other (Fig 2).
An examination of the metric parameters reveals that Zn-Ophenolato bond lengths are in the range
of 2.02-2014
different type nitrogens are coordinated to each Zn(II) ions. Bond lengths of coordinated imino
nitrogens are in the range of 2.03 2.04 Å, which are slightly longer than those of coordinated
nitrogen of thiocyanate anion nitrogen [Zn NThiocyanate = 1.94-1.97 Å]. The bond distance of Zn-
S is 2.468 (1) Å. These data are similar to those found in the literature [47-49].
Å which is relatively shorter than Zn-OOMe bond lengths (2.48-2.60 Å). Two
−
−

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a)
b)
Figure 1. (a) Molecular structure of
numbering is also shown in the picture for the dinuclear unit in the 1D single chain of 1. (b)
Asymmetric unit of complex (hydrogen atoms have been omitted for clarity).
1(hydrogen atoms have been omitted for clarity).The
1

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Figure 2. Perspective view of the crystal packing of
1 with extended H-bonding feature along
the b axis.
a)
b)
Figure 3. (a) Distorted square pyramidal and (b) distorted octahedral geometry around Zn(II)
ion.

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4. Results and discussion
4.1 Synthesis and characterization of Complex 1
We have unambiguously used one-pot synthetic methodology to obtain complex
1 where 1:1:1
molar ratio of the respective Zinc(II) acetate dehydrate, di-compartmental Schiff base (H2L1) and
KSCN has been used in methanol solvent medium at room temperature to yield light yellow
colored plate shaped Zn(II) coordination polymer. The synthesized complex
1 has been
characterized by different micro analytical techniques 1H NMR, FT IR and UV-Vis spectroscopic
study. Our synthesized light yellow complex
1 is stable over long period of time in powdered
form as well as crystalline states and readily soluble in organic solvent like DMSO, DMF,
CH3CN, but insoluble in water. Several weak bands in the range 2960-2870 cm-1 are clearly
observed in complex 1, which is attributed to the aliphatic C-H stretching vibration [50]
intense strong band at 1627 cm-1 for complex
compared to that of the free Schiff base ligand (H2L1) indicating coordination of the imino
exhibits sharp νSCN 2146-2086 cm-1
. An
1
is shifted considerably towards lower frequencies
nitrogen atom with the Zn(II) metal centers [51]. Complex
1
bands suggesting [SCN]-1 coordinating mode towards Zn(II) metal ions [Figure S1-S2]. Further
νSCN 2146-2086 bands have become bifurcated indicating two different coordinating mode
during Zn(II) coordination polymer formation
broad transition at 354 nm presumably due to n
room temperature [52, 53] Figure S3].
4.2 Active Photoluminescence behavior of complex 1
We have studied photoluminescence properties individually for Schiff base ligand (H2L1) and
complex to find out the silent or active nature of fluorescence since fluorescence active
(
Figure S1). Complex
1 exhibits ligand–based
→
π
or π→π*
transitions in DMSO solution at
[
1

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property of complex
1
opens up the new possibility for photochemical applications [54-60]. On
this ground fluorescence properties of Schiff base ligand and its respective 1D chain CP of
complex were studied at room temperature (298 K) in DMSO solvent. Generally a metal ion
1
enhances or quenches fluorescence emission in presence of Schiff base ligand containing
aromatic ring structure. Since Zn(II) ion has no optical spectroscopic signature due to its closed–
shell 3d10 configuration, Zn(II) ion is very difficult to oxidize or reduce. Therefore, it is
expected that complex
1 shows no emission emanating mainly from metal-centered
MLCT/LMCT excited states. Here the emission may be assigned to the intraligand (π→π*
)
fluorescence. The above fluorescence can be elucidated on the basis of
fluorescence intensity’. Normally Zn(II) metal ion enhances or quenches fluorescence emission
in presence Schiff base ligand that contains aromatic cloud ring system and ligand potential
‘chelation mediated
π
donor centers (nitrogen and oxygen) are selectively bonded with respective metal ion .
Quenching of metal ions in presence of Schiff base ligand during complex formation via
different donor center (N, O) is a rather common fact which is explained by a process like
magnetic perturbation, redox activity and electronic energy transfer. In the absence of suitable
metal ions fluorescence property of the ligand is probably quenched by the occurrence of
photoinduced electron transfer (PET) process due to presence of ligand donor atoms like N, O
nonbonding electrons pairs. Such PET process is prevented by the Schiff base ligands when its
nonbonding electron pairs gets stable being complexed with Zn(II) metal center. Fluorescence
graphical plot reveals that Schiff base ligand exhibits emission at 390 nm (Fig 4a) while complex
1
shows emission at 454 nm upon excitation at 354 nm (Fig. 4b). The red shift as well as greater
intensity of complex is presumably due to the conformational rigidity of the ligand upon
complexation or strong ligand donor centers (N,O) binding with Zn(II) metal. The overall
1

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process is referred as ‘chelation enhancement fluorescence’ [CHEF] [61-65]. From emission
spectral curve Figure 4(a) of Schiff base ligand (H2L1), we observed that an emission maximum
is bathochromically shifted as compared to Schiff base ligand (H2L1). This is mainly due to the
methoxy group incorporation on the salen structural skeleton of the ligand. A similar absorption
and emission maxima have been observed for tridentate Schiff base ligand with a methoxy group
in ortho position of the phenol moiety [66]. Reported Schiff base ligand quantum yield is very
low and this is identical with Schiff base (H2L0) N,N’-bis(salicylidene)-1,3-diaminopentane [67].
However, the introduction of methoxy substituent in the ortho position of the phenol ring is also
responsible for red shift emission maxima of Schiff base. Beside for bromine or chlorine
substituted salicylidene structural skeleton Schiff base ligands induce a noticeable decrease of
the quantum yields in comparison with ligand (H2L1) [67]. The luminescence spectral nature
depicted in [Figure 4b] are typically common for Salen-type Schiff-base Zn(II) complexes where
only intraligand π→π* transition can be positively assigned [ 68,69]. We have calculated
Fluorescence quantum yield for complex
the secondary standard ( = 0.57 in water) and thus quantum yield value for complex 1was
found to be 0.01635. Again with reference to highly luminescent Zn(salen) complexes [67], the
reason for weak luminescent of complex is due to the additional non-radiative deactivation
1 by employing equation (1) using quinine sulfate as
Φ
1
pathways. Apart from, one additional possibility in this respect through electron transfer takes
place in presence isothiocyanate anions [70, 71].

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Table 2. Photo-physical parameters of Schiff base ligand (H2L1
) and complex 1 in DMSO
solvent at room temperature 298 K.
Compound
Abssorption (λmax), nm
Excitation (λmax), nm Emission (λmax), nm
Schiff base(H2L1)
258 & 398 nm
332 nm
354 nm
390 nm
454 nm
Complex
1
230, 265 & 345 nm
a)
b)
Figure 4. (a) Emission spectra of Schiff base ligand (H2L1
) in DMSO solution at 298 K. (b)
Absorption and emission spectra of complex in DMSO solution.
1

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5. Antimicrobial screening of complex 1
Complex exhibited antibacterial potency against all five bacterial strains. The MIC values and
growth inhibition zone diameter for the complexes against the tested bacterial strains are shown
in Figure 5 and 6 respectively. Complex had encouraging potentiality to inhibit the growth of
1
1
B. subtilis 6633 and P. vulgaris OX19 in contrast to E. aerogenes 10102 and S. Typhi SRC that
showed less susceptibility to them. In vitro growth curve of four bacterial strains (Bacillus
subtilis 6633, Enterobacter aerogenes 10102, Proteus vulgaris OX19 and Salmonella enterica
ser. typhi SRC) in presence of complex
differences (LSD test; p < 0.05) in the inhibition pattern of bacterial growth subject to selected
complex excepting S. typhi. Complex 1 showed reasonable efficacy as potential antimicrobial
agent in rendering bacterial growth inhibition. The results showed that complex had a wide
spectrum of antibacterial activity. Moreover both Gram positive and Gram negative bacteria
were similarly susceptible to this complex . The growth kinetics study subjected to
antimicrobial candidates proved that the tested complex 1 had encouraging efficiency to hinder
1 are shown in Figure 7. It reflected distinct treatment
1
1
1
the bacterial growth as a bacteriostatic agent. Hence, it can be concluded that complex
promoted as potential broad spectrum antimicrobial agents.
1 can be

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Figure 5. MIC values (µg/mL) and bacterial growth inhibition zone diameter (mm) of the
complex
1 and amoxicillin (the reference antimicrobial agent) to the tested bacterial strains. All
data were taken in triplicate.

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Figure 6. Bacterial growth inhibition zone diameter (mm) of the complex1and amoxicillin (the
reference antimicrobial agent) to the tested bacterial strains. All data were taken in triplicate and
error bars shows standard deviation.

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Figure 7. In vitro growth curves of (a) Bacillus subtilis 6633, (b) Enterobacter aerogenes 10102,
(c) Proteus vulgaris OX19 and (d) Salmonella enterica ser. typhi SRC against complex 1, all data
were taken in triplicate and error bars show standard deviation.

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6. DFT analysis
Geometry optimization of complex
level[72] in ground state using density functional theory (DFT) calculations[73]. The frontier
orbital’s of HOMO and LUMO of Zn(II) coordination polymer complex is shown in Figure 8.
1
was carried out on basis set 6-31G(d) at the B3LYP
1
Figure 8.The optimized structure, HOMO and LUMO orbital of complex
From optimized structure of complex the bond lengths of Zn–S1 and Zn-S2 atoms are 1.97Å
and 1.94Å and bond angle S-Zn2-S of 124, while N-Zn-N is 101. The bond lengths of Zn1-N and
Zn1-O atoms are 2.04Å and 2.03Å respectively. From Figure 8 it is apparent that electron
1.
1
̊
̊

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densities in HOMO plot of complex
1
has largely localized on o-vaniline aromatic ring section
and in LUMO plot electrons density are localized on di-amine propane chain and partly on o-
vaniline ring moiety. The HOMO-LUMO energy gap in the ground state of complex
1 has been
predicted to be 0.35257 eV. The electronic cloud distribution of HOMO and LUMO in singlet
excited state localizes largely on Schiff base ligand. Suggesting the absorption transition is
mainly due to the intraligand charge transfer (ILCT or π → π*) and partly by ligand-to-metal
charger transfer (LMCT), metal-to-ligand charger transfer (MLCT) and metal centered (MC)
transitions which is also supported by UV-Vis absorption spectra.
7. Hirshfeld Surface analysis
Hirshfeld surface and 2D fingerprint plot generated from crystal data of complex
explorer v. 3.1[74] are shown in Figure.9a and 9b. The colour mapping and the shape of the three
dimensional Hirshfeld surfaces of complex show the different intermolecular interactions
1 using crystal
1
present in the crystal packing. The red spots on the surfaces indicate the close-contact
interactions, which are mainly responsible for the molecular packing in the crystals. Apart by
hydrogen bonding, the crystal packing of complex
1 is controlled by dominant interactions
involving S···H, N···H and O···H contacts, which are observed as red spots on the Hirshfeld
surfaces shown in Figure 10 (a-d). The % of H-bonding interaction data with S, N and O atoms
are given in Table 3. From table 3, it is clear that S....H interaction dominates with 15.9%
contributing highest % for the molecular packing stability.

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Table 3. Percentage interactions of H-bonding with S, N and O atoms in complex 1.
S.No
1.
Interaction
S....H
%
15.9
5.9
2.
N....H
3.
O....H
3.9
Figure 9. Hirshfeld surfaces of complex 1 mapped with (a) dnorm property, the molecules in
tube/licorice representation within the transparent surface maps and (b) Shape Index

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Figure 10. (a-d) Hirshfeld 2D fingerprint plots of intermolecular contacts with di and de-
ranging from 0.3 to 2.8 Å (a) all interactions (b) S....H with 15.9% (c) N....H with 5.9% (d) O....H
with 3.9% interaction
8. Conclusion
In this work, we have reported the synthesis of a a one-dimensional polynuclear zinc(II) complex
using a one-step self-assembly process from zinc acetate, ptassium thiocyanate, Schiff base
(L1H2
yielded the polymer of [Zn2L1(µ1,3-SCN)(
)
in methanol medium. The investigation shows that in situ formation of building blocks
1SCN)]n (
1) where two different environment of
η
Zn(II) ions are present. Apart from that [SCN]- ion acts as end to end bridging fashion to
accomplish the formation of 1D chain as well as terminal ligand to satisfy the charge and
coordination. Photoluminescent study revealed that enhanced red shift fluorescence intensities of
complex
1
compared to that of Schiff base ligand (H2L1) in presence of [SCN]-1 pseudohalide ion
exhibited a
confirmed its credential as a potential photoactive candidate. Besides, complex
1
strong antimicrobial activity towards some important Gram +ve and Gram–ve bacteria. As a
complementary revelation Hirshfeld surface analysis via DFT has been investigated for our
synthesized complex 1.

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8. Supplementary data
Certain selected crystal metrical parameters related to Complex
1
are shown in Table S1 and
Figure S1-S2 as supplementary materials. Figure S2 shows ligand IR spectra as supplementary
material. CCDC 1501365 contains the supplementary crystallographic data (excluding structure
factors) in CIF format for the structure reported of complex 1. The 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.
Acknowledgements
This research work did not receive any specific grant from funding agencies in the public,
commercial or not-profit sectors. Prof. Dhrubajyoti Majumdar thanks to Department of
Chemistry, Tamralipta Mahavidyalaya, Tamluk, Purba Medinipur, Institute of Infrastructure
Technology Research and Management (IITRAM) Ahmedabad 380026; Gujarat, Department of
Ecological Studies, University of Kalyani, Kalyani-741235 , West Bengal, and finally GITAM
University, Hyderabad Campus, Hyderabab-502329, India for giving the necessary laboratory,
library and research facilities. Authors are highly grateful to Vidyasagar University,
Paschimmedinipur, India,West Bengal for providing assistance of different spectroscopic
instrumental facilities specially for IR & UV-vis study. Authors also deeply acknowledge the
access of Perkin-Elmer Spectrofluorimeter facility at the Department of Chemistry, Calcutta
University, Kolkata, India for the Fluorescence study. We thank to Mr. Sudipta Panja, IIT,
Kharagpur-721302, West Bengal, for access of Fluorescence quantum yield to his experimental
facility.