Synthesis, spectral and structural studies on NiS2PN and NiS2P2 chromophores and use of Ni(II) dithiocarbamate to synthesize nickel sulfide and nickel oxide for photodegradation of dyes

Article abstract of DOI:10.1016/j.molstruc.2020.128704

The substitution of one of the dithiocarbamate ligands in homoleptic [Ni(dtc)₂] (1) complex (dtc = N,N-di(4-methoxybenzyl)dithiocarbamate) with the phosphine ligands gave heteroleptic [Ni(dtc)(PPh₃)(NCS)] (2), [Ni(dtc)(PPh₃

Full text of DOI:10.1016/j.molstruc.2020.128704

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Synthesis, spectral and structural studies on NiS PN and NiS P chromophores
2
2 2
and use of Ni(II) dithiocarbamate to synthesize nickel sulfide and nickel oxide for
photodegradation of dyes
P. Lakshmanan, S. Thirumaran, Samuele Ciattini
PII:
S0022-2860(20)31029-2
DOI:
https://doi.org/10.1016/j.molstruc.2020.128704
MOLSTR 128704
Reference:
To appear in: Journal of Molecular Structure
Received Date: 30 April 2020
Revised Date: 10 June 2020
Accepted Date: 12 June 2020
Please cite this article as: P. Lakshmanan, S. Thirumaran, S. Ciattini, Synthesis, spectral and structural
studies on NiS PN and NiS P chromophores and use of Ni(II) dithiocarbamate to synthesize nickel
2
2 2
sulfide and nickel oxide for photodegradation of dyes, Journal of Molecular Structure (2020), doi: https://
doi.org/10.1016/j.molstruc.2020.128704.
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CrediT authorship contribution statement
P. Lakshmanan: Synthesis and spectral measurements of complexes and nanoparticles,
theoretical calculations and writing initial manuscript. S. Thirumaran: Conceptualization,
supervision, review and editing. Samuele Ciattini: Single crystal X-ray diffraction data
collection and determination of complex structures using software.

Synthesis, spectral and structural studies on NiS2PN and NiS2P2
chromophores and use of Ni(II) dithiocarbamate to synthesize nickel sulfide
and nickel oxide for photodegradation of dyes
P. Lakshmanana, S. Thirumarana* and Samuele Ciattinib
a Department of Chemistry, Annamalai University, Annamalinagar- 608 002, Tamil Nadu, India.
b Centro di Cristallografia Strutturale, Polo Scientifio di Sesto Fiorentino, Via della Lastruccia No. 3, 50019 Sesto
Fiorentino, Firenze, Italy.
*Corresponding author
Dr. S. Thirumaran
Department of Chemistry
Annamalai University
Annamalainagar 608 002
Tamil Nadu, INDIA
Tel: +91 9842897597
E-mail: sthirumaran@yahoo.com

Synthesis, spectral and structural studies on NiS2PN and NiS2P2
chromophores and use of Ni(II) dithiocarbamate to synthesize nickel sulfide
and nickel oxide for photodegradation of dyes
P. Lakshmanana, S. Thirumarana* and Samuele Ciattinib
a Department of Chemistry, Annamalai University, Annamalinagar- 608 002, Tamil Nadu, India.
b Centro di Cristallografia Strutturale, Polo Scientifio di Sesto Fiorentino, Via della Lastruccia No. 3, 50019 Sesto
Fiorentino, Firenze, Italy.
Abstract
The substitution of one of the dithiocarbamate ligands in homoleptic [Ni(dtc)2] (1)
complex (dtc = N,N-di(4-methoxybenzyl)dithiocarbamate) with the phosphine ligands gave
heteroleptic [Ni(dtc)(PPh3)(NCS)] (2), [Ni(dtc)(PPh3)2] ClO4 (3) and [(dtc)(dppe)] ClO4 (4)
complexes. The complexes 2-4 were characterized by elemental analysis, spectroscopy and
single crystal X-ray diffraction analysis. Single crystal X-ray diffraction studies revealed that 2-4
adopt distorted square planar geometry. Non-covalent interactions in 2-4 were quantified using
Hirshfeld surface analysis. The study of single crystal X-ray diffraction of 2-4 shows that various
interactions such as C-H...π (chelate), C-H...π, C-H...O and C-H...S among molecules of complexes
2-4, participate in cooperative way to stabilize the supramolecular interactions. DFT calculations
were used to determine the electronic structure and properties of 2. The HOMO-LUMO energy
difference (2.7445 eV) is observed to be small which shows the low kinetic stability of 2.
Nanoparticles of nickel sulfide and nickel oxide were successfully synthesized by solvothermal
and thermal decomposition of 1, respectively and characterized by powder X-ray diffraction
(PXRD), High Resolution Scanning Electron Microscopy (HRSEM), Energy Dispersive
Spectroscopy (EDS) and UV Diffuse Reflectance Spectroscopy (UV-DRS). The photocatalytic
activity of both nanoparticles was investigated for degradation of methylene blue and rhodamine

6G under UV irradiation. The results revealed that the nickel oxide has higher photocatalytic
activity than nickel sulfide.
Keywords: Ni(II) complex; Hirshfeld surface analysis; DFT studies; nickel sulfide; nickel
oxide; photodegradation of dyes.
1. Introduction
Metal dithiocarbamate complexes have myriad applications that range over a variety of
fields such as medicine [1-3], vulcanization accelerators [4,5] and catalysis [6-8]. In addition,
they are suitable single source precursors for the preparation of corresponding metal sulfides, [9-
11] which form semiconductor nanocrystals [12], nanotubes, [13] nanofibers [14] and thinfilms
[15,16]. Nickel(II) complexes, both heteroleptic and homoleptic comprising dithiocarbamate
ligands are of interest because of their importance in determination of pollutants [17], sensing
humidity, biological [18-20] and catalytic activities [6]. Since intermolecular interactions
modify the physical properties of the complexes, for many of the presently known and
structurally characterized homoleptic and heteroleptic nickel(II) complexes containing
dithiocarbamates [21,22], the important role of secondary bonds in their supramolecular self
organization has been established. The interactions like C-H...π (chelate ), C-H...π, C-H...S, C-
H...O etc. lead to the formation of supramolecular architecture in such dithiocarbamate
complexes. [Ni(S2CNR2)(Phosphine)n] (n=1(dppe) or 2 (pph3)) complexes exhibit interesting
structural aspects related to intramolecular anagostic interactions of the type Ni...H-C where C is
the ortho carbon atom of the phenyl group of the phosphine [23-26]. Single source precursors
have been utilized to prepare nickel sulfide and nickel oxide nanoparticles and this has resulted
in particles with varying crystalline phases and sizes [11,27,28]. The properties of nanomaterials
depend on size and shape of the particles that give rise to the application in various fields such as
electronic [29], dye-synsitized solar cells [30], catalysis [31,32], nuclear medicine [33] and

energy storage devices[34,35]. Nanoparticles of nickel oxide and nickel sulfide find wide range
of applications including solar cells [36], agricultural [37] and super capacitors [38]. Nickel
oxide and nickel sulfide are versatile wide band gap semiconductor material with band gap
ranging 3.0 -4.0 eV [39-42]. Recently, various size and shape of nickel oxide and nickel sulfide
nanoparticles were prepared using nickel complexes containing dithiocarbamates [11] and
xanthates [43,44]. Photocatalytic degradation of dyes is an effective and distinguishable process
for the removal of dyes from industrial waste water. The photocatalytic process using
semiconductors has attracted much greater attention since it offers effective degradation and
selectivity towards the pollutants in the mixed aqueous solution at low cost with effective
stability and reusability [45-48]. NiS and NiO are efficient catalysts for waste water pollution
abatement [49,50]. Synthesis, spectral and structural studies on bis(N,N-di(4-
methoxybenzyl)dithiocarbamato-S,S’)nickel(II) (1) were reported [51]. Complex 1 exhibits
intermolecular anagostic interactions. Our aim is to substitute one of the dithiocarbamate ligand
in homoleptic complex 1 with phosphine ligand to produce heteroleptic complexes containing
dithiocarbamate and phosphine ligands and to study the effect of phosphine on spectral and
structural properties of heteroleptic complexes. and the intermolecular anagostic interaction in 1
exists in the heteroleptic complexes. In addition, we attempt to prepare nickel sulfide and nickel
oxide nanoparticles from 1 using solvothermal and thermal decomposition methods. In this
study, we report the preparation, spectral and structural studies on [Ni(dtc)(NCS)(PPh3)] (2),
[Ni(dtc)(PPh3)2]ClO4
(3)
and
[Ni(dtc)(dppe)]ClO4
(4)
(dtc
=
N,N-di(4-
methoxybenzyl)dithiocarbamate). In addition, preparation of nickel sulfide nanoparticles from
bis(N,N-di(4-methoxybenzyl)dithiocarbamate-S,S’)nickel(II) (1) by solvothermal method and

nickel oxide nanoparticles by thermal decomposition of 1 and their characterization are
presented. The photocatalytic activity of both nanoparticles is also reported.
2. Experimental
2.1. Materials and methods
All reagents and solvents were purchased from Alfa Aesar and SD fine chemicals and
were used without purification. Microanalyses for C, H and N were obtained from Perkin Elmer
2400 series(II) CHN analyzer. The IR spectra were recorded on Agilent-Cary 650 spectrometer
using the KBr pellets scanning from 4000-600 cm-1. UV-1650 PC Shimadzu UV-Visible
spectrophotometer utilized to record the UV-Vis spectra of the complexes in chloroform
solutions and UV-DRS of nanoparticles. Solution-state 1H and 13C (1H decoupled) NMR spectra
of complexes in CDCl3 were recorded using Bruker 400 MHz operating at 400.13 and 100.62
MHZ, respectively. Structural characterization of nickel sulfide and nickel oxide nanoparticles
was performed using PXRD measurement on X’pert powder X-ray diffractometer. FEI Quanta
FEG 200 High Resolution Scanning Electron Microscope (HRSEM) was used to record HRSEM
images and Energy Dispersive X-ray spectra (EDS) of nickel sulfide and nickel oxide
nanoparticles.
2.2. X-ray crystallography
Single crystal X-ray diffraction data were collected on a Bruker Apex-II CCD
diffractometer using graphite-monochromated Mo-Kα radiation (λ =0.71073 Å) at 100(2) K. The
structures were solved using SHELXT-2014 [52] and refined by full-matrix least squares
methods using SHELXL – 2018 [53]. Molecular graphics were drawn using mercury software
[54]. All non-hydrogen atoms were refined anisotropically and all hydrogen atoms were fixed
geometrically and were allowed refined using a riding model. Lattice parameters and refinement

data for 2-4 are given in Table 1. Crystallographic data for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data Centre (CCDC No.1999683,
1999688 and 1999689 for 2, 3 and 4,respectively). Copies of the data can be obtained free of
charge from the CCDC, Union Road, Cambridge CB1 1EZ, UK (Tel: (+44) 1223-336-408; Fax:
(+44) 1223- 336-003; E-mail: deposit@ccdc.cam.ac.uk).
2. 3. Theoretical studies
Hirshfeld surfaces and finger print plots were calculated by Crystal Explorer 3.1 software
[55,56]. DFT studies were performed with GAUSSIAN-03 programme with the aid of Gauss
view visualization program [57-59]. Optimized structure of 2 was obtained from DFT using the
B3LYP exchange-correlation functional. The 6–311G+(d,p) basis set was used for all main
group elements and the LANL2DZ basis set was used for nickel atom.
2.4. Preparation of bis(N,N-di(4-methoxybenzyl)dithiocarbamato-S,S’)nickel(II) (1)
The bis(N,N-di(4-methoxybenzyl)dithiocarbamato-S,S’)nickel(II) was synthesized by the
method that has been reported earlier by Ravi et. al [51].
2.4.1. Synthesis of complex 2
Complex 2 was prepared by mixing 1 (0.7236 g, 1 mmol), PPh3 (0.5244 g, 2 mmol),
NiCl2.6H2O (0.2376 g, 1 mmol) and NH4SCN (0.1522 g, 2 mmol) in chloroform-methanol
mixture (3:1; 40 mL) and the reaction mixture was refluxed for 3 h. The green colour suspension
changed to purple colour solution. The solution obtained was allowed to cool to room
temperature, filtered and left for 6 days at room temperature which yielded purple red colour
solid. The solid obtained was filtered and dried (Scheme 1).
Colour: purple red; Yield: 72%, mp 211-213 °C. IR (KBr, cm-1): 1509 (vC-N) thioureide;
1024 (vC-S) dithiocarbamate; 2089 (vC-N) thiocyanate. UV-Vis (CHCl3, nm):
λ = 478, 332, 270,

1
248. H NMR (400 MHz, CDCl3, ppm): ꢀ = 3.74 (s, 6H, 4CH3O-C6H4-CH2-N); 4.30, 4.48 (4H,
4CH3O-C6H4-CH2-N); 6.79-7.69 (aromatic protons). 13C NMR (400 MHz, CDCl3, ppm): ꢀ =
49.2 (4CH3O-C6H4-CH2-N); 54.4 (4CH3O-C6H4-CH2-N); ipso carbon 158.8 (Ar-4CH3O); 113.4-
133.2 (other aromatic carbons); 142.9 (NCS); 203.6 (NCS2). C36H33N2NiO2PS3 (%): Elemental
Analysis: Calcd.: C, 60.77; H, 4.67; N, 3.94. Found; C, 60.56; H, 4.63; N, 3.90.
2.4.2. Synthesis of complex 3
Complex 1 (0.7236 g, 1 mmol), PPh3 (0.5244 g, 2 mmol), NiCl2.6H2O (0.2376 g, 1
mmol) and NaClO4 (0.281 g, 2 mmol) were taken in a round bottom flask and refluxed in
chloroform-methanol mixture (3:1, 40 mL) for 3h. The purple red colour solution obtained was
cooled, filtered and left for evaporation at room temperature which gave purple red solid after 5
days. The solid obtained was filtered and dried (Scheme 1).
Colour: purple red. Yield: 68%, mp 136-138 °C. IR (KBr, cm-1): 1508 (vC-N) thioureide;
1
1022 (vC-S) dithiocarbamate; 1083 (vClO4). UV-Vis (CHCl3, nm):
λ
= 448, 402, 324, 260. H
NMR (400 MHz, CDCl3, ppm): ꢀ = 3.76, 3.84 (6H, 4CH3O-C6H4-CH2-N); 4.30-4.63 (three
signals, 4H, 4CH3O-C6H4-CH2-N); 6.91-7.46 (aromatic protons). 13C NMR (400 MHz, CDCl3,
ppm): ꢀ = 49.8, 50.6, 51.3 ( 4CH3O-C6H4-CH2-N); 53.2, 55.4, 55.5 (4CH3O-C6H4-CH2-N); ipso
carbon 160.0 (Ar-4CH3O); 114.3-134.0 (other aromatic carbons). C53H48ClNNiO6P2S2 (%):
Elemental Analysis: Calcd.: C, 62.71; H, 4.77; N, 1.38. Found; C, 62.53; H, 4.78; N, 1.35.
2.4.3. Synthesis of complex 4
A method similar to that described for the synthesis of 3 was adopted; however
diphenylphosphinoethane (0.7968 g, 2 mmol) was used instead of PPh3 (Scheme 1).

Colour: Red. Yield: 70%, mp 228-230 °C. IR (KBr, cm-1): 1506 (vC-N) thioureide;
1
1027 (vC-S) dithiocarbamate;. 1075 (vClO4). UV-Vis (CHCl3, nm):
λ
= 496, 309, 272, 247. H
NMR (400 MHz, CDCl3, ppm): ꢀ =2.62 (d, 4H, P-CH2-CH2-P); 3.74 (s, 6H, 4CH3O-C6H4-CH2-
N); 4.57 (s, 4H, 4CH3O-C6H4-CH2-N), 6.81-7.70 (aromatic protons). 13C NMR (400 MHz,
CDCl3, ppm): ꢀ = 26.3 (P-CH2-CH2-P); 50.4 (4CH3O-C6H4-CH2-N); 55.5 (4CH3O-C6H4-CH2-
N); ipso carbon 160.0 (Ar-4CH3O); 114.6-132.9 (other aromatic carbons); 142.9 (NCS); 203.0
(NCS2). Anal. Calcd. for Chemical Formula: C43H42ClNNiO6P2S2 (%): Elemental Analysis:
Calcd.: C, 58.09; H, 4.76; N, 1.58. Found; C, 57.99; H, 4.72; N, 1.56.
2.4.4. Preparation of nickel sulfide
Complex 1 (0.5 g) was taken in a round bottom flask and dissolved in ethylenediamine
(30 mL). The contents of the flask were refluxed for 15 min. The solution was filtered using
sintered glass crucible and dried. The precipitate was transferred to silica crucible and placed in
an electrical furnace at 400 °C for 30 min. The precipitate analyzed to nickel sulfide (NiS).
2.4.5. Preparation of nickel oxide
Complex 1 (1 g) was taken in a silica crucible and then placed in an electrical furnace and
heated at a rate of 5 °C min-1 in presence of air upto 650 °C. After 30 min, the resulting residue
was collected and analyzed to nickel oxide (NiO).
2.5. Photocatalytic activity measurements
In this process, 100 mg of the photocatalyst (nickel sulfide and nickel oxide) was
suspended in an aqueous solution of 40 ml of 1x10-5 M methylene blue or rhodamine-6G dyes
and left for 30 min in the dark prior to irradiation to create an adsorption – desorbption
equilibrium between dye and photocatalyst. The reaction mixture was irradiated by UV light
from mercury vapour lamp in a photocatalytic instrument with water cooling device. The

concentration of the dye solution was measured UV-Vis spectrophotometerically (UV-1650 PC
Shimadzu UV-Visible spectrophotometer) at a time interval of 30, 60, 90, 120, 150 and 180 min
by withdrawing aliquots of the dye solution. In addition, the dye degradation efficiency at the
beginning of the experiment (t=0), in dark (absence of light and catalyst), in dark with catalyst
and in presence of light but not catalyst is also determined.
3. Results and discussion
3.1. Synthesis
The synthesis of complexes 2-4 were performed as shown in scheme 1. Synthesis of
complex
2
was achieved by refluxing bis(N,N-di(4-methoxybenzyl)dithiocarbamate-
S,S’)nickel(II) (1) (1 mmol), triphenylphosphine (2 mmol), ammonium thiocyanate (2 mmol)
and nickel chloride hexahydrate (1 mmol) in chloroform – methanol (3:1) mixture. Similarly 3
and 4 were synthesized by refluxing complex 1, sodium perchlorate, nickel chloride and
triphenylphosphine or 1,2-bis(diphenylphospheno)ethane in chloroform : methanol (3:1).
Complexes 2-4 are stable under ambient conditions and freely soluble in halogenated solvents.
Suitable single crystals of 2-4 for X-ray diffraction studies were obtained from slow evaporation
of the chloroform: acetonitrile (1:1) solutions for 2 and 3 and dichloromethane: methanol (1:1)
for 4.
3.2. Spectroscopy
IR, and NMR (1H and 13C) spectra of 2-4 are displayed in Figs. S1-S9. The infrared
spectral bands of metal dithiocarbamate complexes in the region of 1450–1550 and 950-1050
cm-1 are of interest because C-N (thioureide) and C-S stretching vibration appear in these
regions, respectively [3]. The later value indicates the coordination mode

(bidentate/monodentate) of dithiocarbamate ligands. The vC-S band appeared as the single band in
the region of 1022–1027 cm-1 in complexes 2-4 alluding bidentate coordination mode of
dithiocarbamate ligand to metal center in the complexes. The vC-N band of complexes 2-4
appeared around 1505 cm-1 which reflects the partial double band character of the N-CS2 bond.
The bands observed between 2920 and 2835 cm-1 correspond to methylene and methyl groups
(aliphatic C-H stretching vibrations) for all complexes.
Electronic absorption spectra of complexes 2-4 were recorded in chloroform. All the
complexes exhibited absorption bands between 247 and 402 nm are due to intraligand π-π*
transitions associated to N-C=S and S-C=S groups [60]. An absorption band observed for 2-4 at
478, 448 and 496 nm respectively is owing to the d-d transitions corresponding to square planar
geometry around the metal center [61].
The methylprotons of the methoxybenzyl group appeared around 3.74 ppm. The
methylene protons of dithiocarbamate ligands in 2 and 3 observed as two (4.30 and 4.48 ppm)
and three signals (4.30-4.63 ppm) may be attributed to the existence of dynamic process in the
solution [62]. 1H NMR spectrum of 4 shows a singlet for the methylene groups of
dithiocarbamate ligands. The protons of two methylene (-CH2-CH2-) groups bridging the two
phosphorus atoms in complex 4 were observed at 2.65 ppm.
In the 13C NMR spectra, the aliphatic carbons of 2 and 3 and methylene carbons of dppe
appeared as doublets or triplets due to the existence of dynamic process [62]. A weak signal
observed at 142.9 ppm for 2 is attributed to the carbon of thiocynate ion. The presence of a peak
13
around 203 ppm in C NMR spectra of 2 and 4 is assigned for the N13CS2 carbon atoms in the
complexes [63]. The NCS2 carbon chemical shift moved upfield from 208.4 ppm for parent
homoleptic complex 1 [51] to around 203 ppm for heteroleptic complexes 2 and 4. This upfield

shift is due to the presence of phosphine (π-acceptor) ligands in 2 and 4 which increase the
mobilization of electron density from the dithiocarbamate moiety toward the metal atom.
3.3. Crystal Structure of 2
ORTEP of 2-4 are displayed in Fig. 1. Crystal structure of complex 2 shows square
planar geometry with two S atoms of dithiocarbamate ligand occupying two adjacent
coordination sites of Ni(II) while nitrogen of SCN- and phosphorus of PPh3 occupy the
remaining sites. The largest distortion from the normal square planar geometry arises from
bidentate dithiocarbamate ligand (S3-Ni-S2 of 78.69(2)°). The τ4 = 0.13 indicates that the
coordination geometry is seesaw structure (τ4 is defined as 360 – (α+β)/141 where α and β are
the two trans angles, with τ4 = 1.00, 0.85, 0.64-0.07, and 0.00 for perfect tetrahedral, trigonal
pyramid, seesaw and perfect square planar, respectively) [64]. The S-Ni-S bite angle in 2
(78.69(2)°) is less than that of S-Ni-S bite angle in 1 (79.68(3)°) [51]. This may be due to steric
effect of bulky PPh3 present in 2. In 1, the Ni-S bonds [Ni-S11=2.1920(8) Å] and [Ni-
S13=2.2097(9) Å] are symmetric. But in this complex 2, Ni-S bond distance are asymmetric.
The asymmetry observed in the Ni-S distance is typical for square planar S2PN chromophore
systems [11, 24] and reflects the trans effect of the ligand. Ni-S2 (2.2312(6) Å) bond length is
longer than Ni-S3 (2.1648(6) Å) bond length with ∆(Ni-S) of 0.0664 Å. The Ni-N distance
(1.8534(18) Å) and Ni-P distance (2.1933(6) Å) are comparable to those of nickel complexes
containing dithiocarbamate, NCS- and PPh3 ligands [24, 25]. Other selected bond lengths and
angles are given in Table 2 along with calculated values.
The crystal packing of the complexes are stabilized by C-H...π (chelate), C-H...π, C-H...O
and C-H...S intermolecular interactions (Table S1). In the crystal structure of 2, C5-H5...π,

(phenyl ring of methoxy phenyl group) interaction between two molecules related by an
inversion form dimers and generates a macrocyclic ring (Fig. S10). The H9 hydrogen atom of
parent molecule of 2 is in contact with the centroid of the chelate ring of the partner molecule
and the H4 atom of the partner molecule is in contact with centroid of the chelate ring of parent
molecule (Fig. 2). Two C-H...O intermolecular interactions (C16-H16...O2 = 2.498 Å) and
(C28A-H28A...O2 = 2.433 Å) leads to the formation of layer (Fig. S11). Further, the stabilizing
of complex 2 involves a trifurcated H bond, in the sense that the S4 atom of thiocyanate engages
in H- bond simultaneously with three H atoms from three different moieties (Fig. 3 and Table
S1). All these interaction are responsible for the supramolecular architecture in the crystal
packing.
3.4. Crystal Structure of 3
ORTEP of 3 is shown in Fig. 1. Selected bond lengths and angles are given in Table 2.
Single crystal X-ray structural studies on complex 3 shows that it crystallizes in triclinic crystal
lattice with space group Pī having distorted square planar geometry, to which one
dithiocarbamate anion is coordinated through two sulfur (S1 and S2) atoms and two triphenyl
phosphine coordinated through two phosphorus (P1 and P2) atoms to complete the coordination
sphere (Fig. 1). The coordination geometry around nickel(II) is seesaw as seen in the τ4 value of
0.15 [64]. The cis angles, S-Ni-P angles (P2-Ni-S2=92.668(12)° and P1-Ni-S13=89.478(12)°)
are near 90°, while the bite angle S-Ni-S (78.726(12)°) deviates ca. 11.3°, the P-Ni-P
(99.25(1)°) exhibiting opposite deviation to 9.3° due to the steric effect of the PPh3. The slight
asymmetry in Ni-S (Ni-S1=2.2234(3) Å and Ni-S2=2.2041(3) Å) and Ni-P (Ni-P1=2.2192(3) Å
and Ni-P2=2.1910(3) Å) distance is also due to the bulkiness of the two PPh3 ligands.

The O3-O5 oxygen atoms of perchlorate ion exhibits thermal disorder. The major
component has a site occupancy factor of 0.807(4) and the atoms of the minor component were
refined isotropically. The perchlorate ion plays a crucial role in the supramolecular aggregation.
There is an extensive hydrogen bonding interactions between the oxygen atoms of perchlorate
anion and hydrogen atoms of nickel(II) complex cation which leads to the formation of three
dimensional array (Fig. S12, Table S2). A dimer is formed by C-H...π (chelate) interaction (Fig.
4). The solid state structure is further stabilized by C-H...O and C-H...S interactions (C41-
H41...O1=2.770 Å and C17-H17B...S2=2.907 Å) (Figs. S13 and S14).
3.5. Crystal Structure of 4
The asymmetric unit of 4 contains two crystallographically independent molecules (Fig.
1). The difference in geometrical parameters between the two molecules (a molecule containing
Ni1 and another molecule containing Ni2) are insignificant (Table 3). So the structural properties
of only molecule containing Ni1 are discussed in detail. In complex 4, Ni(II) is four coordinate
distorted square planar geometry in which nickel binds with two S atoms of the bidentate
dithiocarbamate ligand and two P atoms of dppe ligand. The τ4 –value (0.12) for 4 confirms the
seesaw structure around the metal center. The Ni-S (2.2045(4) and 2.2086(4) Å) and Ni-P
(2.1495(4) and 2.1622(4) Å) bond distances are symmetric which are within the range reported
for similar metal dithiocarbamate complexes containing dppe. The bond angles S1-Ni1-P2
(168.309(17)°) and S2-Ni1-P1(174.589(16)°) are trans angles and the other two cis angles S1-
Ni1-P1 and S2-Ni1-P2 are recorded to be 98.064(15)° and 95.652(15)° respectively. This
variations of angle from that expected for a perfect square planar geometry is due to the presence
of different ligands around the metal center and decrease in the bite angles of dithiocarbamate
-
(S1-Ni1-S2=80.029(15)°) and dppe (P1-Ni1-P2=87.165(15)°). The ClO4 group lies out of the

coordination sphere. One of the perchlorate ions (occupancy factor: 0.5926(16):0.4074(16)) and
a methoxy group (occupancy factor; 0.567(10) : 0.433(10)) were disordered.
The Ni-P distances in 4 (mean: 2.1599Å) are shorter than those in 2 and 3 (2.1933 and
mean: 2.2051Å for 2 and 3 respectively). This indicates that the chelating dppe strongly bound to
the central metal ion compared to those of PPh3.The τ4 value and X-Ni-P angles follow the order:
4 (τ4 = 0.12 and P-Ni-P = 86.827(16)°) < 2 (τ4 = 0.13 and N-Ni-P = 92.13(6)°) < 3 (τ4 = 0.15 and
P-Ni-P = 99.25(1)°). These are all due to the presence of bulky two monodentate
triphenylphosphine ligands in complex 3.
The molecules in 4 are held together via non-bonded C-H...̟ interactions with C5-H5...Cg
(C24-C29) distances of 2.607Å (Fig. S15), resulting in a dimeric structure. Intermolecular
C-H...O interaction (C42-H42A…O2=2.307 Å) leads to the formation of linear chain (Fig. 5).
Along with other interactions, numerous C-H...O interactions between the hydrogen atoms of
Ni(II) complex cation and oxygen atoms of the tetrahedral perchlorate anions, including
bifurcated and trifurcated hydrogen bonding interactions are observed. These extended hydrogen
bond network are linked to give supramolecular architecture (Fig. S16 and S17, Table S3).
3.6. Anagostic interactions in 3 and 4
The main feature of structures 3 and 4 is based on the short intramolecular distance
between the nickel atom and the ortho hydrogen atom of phenyl group in phosphine ligands. For
heteroleptic nickel(II) complexes, this kind of interaction was reported by several authors
[24,65]. The C17-H23...Ni in 3 and C19-H19...Ni1 and C83-H83...Ni2 in 4 are characterized as
anagostic interactions and the bond parameters H...Ni (2.809Å for 3 and 2.755 Å and 2.745 Å for
4) and C-H...Ni angle (120.84° for 3 and 117.01°and 118.46° for 4) are within the ranges of the
corresponding geometric parameters of C-H...Ni anagostic interactions: 2.3-2.9 Å and 110-170°,

respectively (Fig. 6). The discussed intramolecular interactions result from packing effects, steric
restrictions of bulky ligands and the d8 electronic configuration of nickel [24,65].
3.7. Hirshfeld surface analysis
The molecular packing in complexes 2-4 was also studied by calculating the relative
composition of each intermolecular contact present in the structure through Hirshfeld surface
analysis. The Hirshfeld surface analysis was performed with Crystal Explorer 3.1. Selected two
dimensional finger print plots are shown in Fig. 7. In general, the intermolecular H...H and
C...H/H...C close contacts dominates in 2-4. The percentage of H...H close contacts increases in
the following order 4(45.7%) < 2 (46.7%) < 3 (50.6%) (Fig. 8). The higher value for 3 may be
due to the presence of two molecules of hydrogen rich triphenylphosphine. Further, the results
show that O...H/H...O interactions in 3 (21.6%) and 4 (22.7%) are relatively high due to the
presence of oxygen rich perchlorate ions in the molecules. In complex 2, the contact between
hydrogen and sulphur (H...S/S...H) is another major interaction comprising 14.7% of all other
interactions. The Hirshfeld surfaces are colour mapped with the normalized contact distance,
dnorm, from red (distances shorter than the sum of the van der Waals radii) through white to blue
(distances longer than the sum of the van der Waals radii). The positions of the strong O...H
hydrogen bonds are indicated by the red regions on the Hirshfeld surface (Fig. 9). Figs. S18-S20
shows the important intermolecular O...H, S...H and Cl-O...H interactions in complexes 2-4.
3.8. DFT studies on 2
3.8.1. Optimized structure parameters
The optimized structure with atomic numbering scheme for 2 is given in Fig. S21. The
optimized geometrical parameters namely bond lengths and bond angles are collected in Table 2.

The optimized geometrical parameters are compared with the experimental data of 2. For the
comparison of geometrical parameters correlation graphs between the calculated and
experimental parameters of bond lengths and angles for 2 are shown in Fig. S22. The correlation
values (R2) for bond lengths and bond angles are 99%. These results indicate the good agreement
between the calculated and experimental bond parameters.
3.8.2. Molecular electrostatic potential (MEP)
Molecular electrostatic potential surface map is displayed in Fig. 10. MEP surface
analysis is performed to study the reactivity of the complex in both electrophilic and nucleophilic
reactions and determine the sites of electrophile (positively charged species) and nucleophile
(negatively charged species). The surfaces containing different electrostatic potential values are
indicated by different colours. The increasing order of electrostatic potentials are shown in
red<orange<yellow<green<blue colours [66]. In general, red colour map indicates the maximum
negative region promoting the site for electrophilic while the positive region (blue colour region)
promoting the site for nuceophilic. The MEP map (Fig. 10) shows that the sites for electrophilic
attack localized on S atom of thiocyanate. The region very close to S atoms (S2 and S3) of
dithiocarbamate and oxygen atoms (O1 and O2) of methoxy group appear yellow colour (less
electropositive). It is also seen in Fig. 9 that, electropositive region (blue colour) covers the
hydrogen atoms of NCH2 and OCH3 groups and H15-H17 of PPh3.
3.8.3. Frontier molecular orbitals (FMOs)
Frontier molecular orbitals are called as highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO). These orbitals play an important role in
describing the chemical reactivity descriptors and chemical behavior of the complexes [67]. In
complex 2, the HOMO is mainly localized on N and S atoms of thiocyanate ion, while the

LUMO is mainly located on two S atoms of dithiocarbamate ligand, central metal ion , N of
thiocyanate and P atoms of triphenylphosphine. The band gap energy between the HOMO
(-5.11eV) and LUMO (-2.37 eV) is 2.74 eV (Fig. 11). The small band gap energy of 2 indicates
that this complex is more polarisable, highly reactive, low kinetic stability and is also termed as
soft molecule [67]. The softness (σ), chemical hardness (η), absolute electro negativity (χ) and
chemical potential (µ) can be calculated using energy of HOMO and LUMO [68]. The values of
global reactivity indicators are calculated by using the following equations and are given in
Table 4. The low chemical hardness (η) value (1.387 eV) reveals the high reactivity of 2.
Complex 2 possesses high electronegativity (3.74 eV), so it is an electron acceptor.
χ = (IP + EA)/2, η = -(IP-EA)/2, σ = 1/η and µ = -(IP+EA)/2
where IP (ionization potential) = -EHOMO and EA(electron affinity) = -ELUMO
3.9. Characterization of nickel sulfide and nickel oxide nanopartilces
3.9.1. PXRD pattern:
The PXRD patterns are shown in Fig. 12. The peaks observed in the XRD pattern of nickel
sulfide correspond to the hexagonal Ni7±xS6 (JCPDS card No: 51-0717) and monoclinic Ni0.96
S
(JCPDS card No: 50-1791) phases. Nickel sulfide with mixture of various compositions were
obtained from nickel(II) dithiocarbamate complexes such as a mixture of Ni3S4 and NiS from
[bis(N,N-dibutyldithiocarbamato-S,S’)nickel(II) [69] and Ni3S4 and NiS2 mixture from bis(N-
pyrrole-2ylmethyl)-N-furfuryldithiocarbamato-S,S’)nickel(II) [11]. The X-ray diffraction pattern
of nickel oxide reveals three peaks at 2θ angles 37.29°, 43.33° and 62.95° which correspond to
(111), (200) and (220) crystal planes of cubic structure. This XRD pattern is in good agreement
with the reported XRD pattern (JCPDS card No: 47-1049). The remaining four low intensity
peaks observed between 2θ = 25 and 36° show the presence of trace amount of nickel sulfate

with nickel oxide. The X-ray diffraction pattern with sharp peaks indicates that the as-prepared
nickel oxide is in crystalline nature.
The crystallite size (D) is calculated using the Debye-Scherrer formula,
The calculated crystallite size for NiS and NiO is 62 and 37 nm, respectively.
3.9.2. HRSEM studies
The morphological features of the as-prepared nickel sulfide and nickel oxide
nonoparticles are studied by high resolution scanning electron microscopic technique. Fig. 13
depicts HRSEM images of nickel sulfide and nickel oxide nanoparticles. The HRSEM images of
nickel sulfide and nickel oxide reveal that both particles are agglomerated small bead like
structures. These agglomerates are mainly assembled by spherical nanoparticles.
3.9.3. EDS analysis
EDS analysis are used to find elemental composition in the products. Energy dispersive
X-ray spectra of as-prepared nickel sulfide and nickel oxide are displayed in Fig. S23. Energy
dispersive X-ray spectrum of product obtained by the solvothermal decomposition of complex 1
confirms the presence of Ni and S and the atomic ratio of Ni/S = (1.0 : 0.97) reveals the
formation of nickel sulfide. Energy dispersive spectrum of product obtained from thermal
decomposition of 1 shows peaks for Ni, O and S which confirms the presence of Ni, O and S.
The atomic ratio of Ni and O formed by EDS analysis (1.0:1.06). The oxygen excess (higher
ratio) and the presence of trace amount of sulfur confirm that a very small amount of nickel
sulfate present with nickel oxide. The formation of NiO and NiSO4 is supported by the
thermogravimetric analysis. The thermogravimetric analysis of Ni(II) dithiocarbamate
complexes in presence of air show that a mixture of NiO and NiSO4 was obtained as a final
residue above 600°C [70].

3.9.4. UV-DRS analysis
Since the optical property of nanoparticles plays an important role in the photocatalytic
activity, the optical property of as prepared nickel sulfide and nickel oxide nanoparticles were
investigated using UV diffused reflectance spectroscopy. From DRS spectrum, the band gap
energy is estimated using Kubelka-Munk equation [71]:
where F(R) is Kubelka-Munk function and R is diffused reflectance. The equation relating F(R)
and absorption coefficient (α) is
The band gap (Eg) can be correlated to the by the relation as follows:
α
(αhv) = A (hv
- Eg)n
This equation can be rewritten as
(αhv) = F (R) hv = A(hv
– Eg)2
The band gap energy value of the NiS and NiO nanoparticles can be found by extrapolating the
2
linear part of plot to (F(R)* h
v
)2 = 0. Plots of (F(R) h
v)
versus photon energy (h
v
) are depicted
in Fig. S24. The band gap energy value of as-prepared nickel sulphide (3.8 eV) is higher than the
bulk nickel sulfide (2.1 eV) [72]. This supports the quantum confinement effects in the
nanoparticles. The band gap of the NiO particles is 3.3 eV, which is similar to the value reported
for nickel oxide nanoparticles [73,74].

3.10. Photodegradation of dyes
The catalytic photodegradation activities of as-prepared NiS and NiO are evaluated by
measuring the degradation of methyleneblue and rhodamine-6G in aqueous solution under UV
light irradiation. The UV-Visible spectra obtained during photodegradation experiment of dyes
in presence of NiS and NiO are shown in Figs. 14 and 15. Almost no degradation of dye was
observed in dark (absence of light and catalyst), in dark with catalyst and in presence of light but
not catalyst. This indicates that the catalyst along with UV light irradiation is important for the
efficient degradation of the dye solutions. It can be seen that the characteristic absorption peak at
661 and 528 nm for methylene blue and rhodamine-6G dyes, respectively decreased gradually
with increasing time in the presence of photocatalyst under UV irradiation indicating the
degradation of dye molecules. The percentage of dye degraded at any time t was calculated using
the following equation.
Percentage of degradation
where A0 is the initial absorbance of dye and At is the absorbance at time t. 59% and
71% of methylene blue were degraded in the presence of NiS and NiO, respectively under UV
irradiation after 180 min, whereas in the case of rhodamine-6G was degraded 71% and 94%,
respectively . Thus NiO is the most efficient photocatalyst for the degradation of methylene blue
and rhodamine-6G. The enhanced photocatalytic activity of nickel oxide compared to nickel
sulfide toward degradation of methylene blue and rhodamine-6G is due to the low band gap
energy of nickel oxide. Low band gap of nickel oxide nanoparticles is helpful for the easy
generation of electron hole pair [75].
The mechanism of photocatalytic degradation of water can be explained by the following
equations :
NiS / NiO + h
v
e– + h+

Oxidation of water with h+ (hole):
H2O + h+
•OH + H+
Reaction of e- with O2 from air (O2) present in solution:
O2 + e–
•O2
–
•
+
•
–
O2 + H
HO2
•
2HO2
O2 + H2O2
•OH + OH–
H2O2 + e–
Oxidation of hydroxide with h+:
OH– + h+
OH•
•
-
Reaction of O2 and •OH with dye leads to the formation of CO2 and H2O :
Dye (methylene blue / rhodamine -6G) + •OH + •O2
CO2 + H2O
–
4. Conclusions
In this study, complexes 2-4 were synthesized and characterized using various spectral
and single crystal X-ray studies. Structures of 2-4 additionally stabilized by various weak
interactions like C-H... (chelate), C-H... , C-H...O and C-H...S involving adjacent moieties in the
π π
crystal. Hirshfeld surface analysis indicated that intermolecular hydrogen bonding interactions
play an important role in the crystal packing of 2-4. Quantum chemical calculations of complex 2
were made at DFT/B3LYP theory level. The theoretical optimization of 2 yielded good
agreements between calculated and experimental geometrical parameters. Nickel sulfide and
nickel oxide nanoparticles were obtained from complex 1 using solvothermal and thermal
decomposition methods and fully characterized. Nickel sulfide and nickel oxide nanoparticles
degraded methylene blue upto 59% and 71%, respectively whereas rhodamine-6G was degraded
upto 71% and 94%. The higher photocatalytic activity of nickel oxide nanoparticles should be
related to its smaller band gap (3.3 eV) compared to those of nickel sulfide (3.8 eV).

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