The first nickel(II) complexes of disubstituted diphenyldithiophosphates: Synthesis, spectroscopic, electrochemical, antifungal and single crystal X-ray analysis

Article abstract of DOI:10.1016/j.poly.2014.01.036

Five novel nickel(II) complexes of disubstituted diphenyldithiophosphates, [{(ArO)₂PS₂}₂Ni] [Ar = 2,4-(CH ₃)₂C₆H₃ (1), 2,5-(CH ₃)₂C₆H₃ (2), 3,4-(CH ₃)₂C₆H₃ (3), 3,5-(CH ₃)₂C₆H₃ (4) and 4-Cl-3-CH ₃C₆H₃ (5)], have been synthesized in aqueous medium and structurally characterized by IR, heteronuclear NMR (¹H, ¹³C and ³¹P) spectroscopic and single crystal X-ray analyses. Complexes 1 and 5 crystallize in the triclinic space group P1?, whereas complex 4 crystallizes in the monoclinic space group P2₁/n. In these complexes, the ligands are coordinated to the nickel ion as a bidentate chelating agent via the two thiolate sulfur atoms, leading to a spirocyclic system. Crystal structure determination of complexes 1, 4 and 5 reveals that the complexes consist of mononuclear units with the nickel(II) ion coordinated in a bis-bidentate fashion with a distorted square planar coordination environment. A cyclic voltammetry experiment was used to probe the redox capabilities of complex 4. The investigated complexes, along with the ligands, have been screened for in vitro antifungal activities against the fungus Penicillium chrysogenum.

Full text of DOI:10.1016/j.poly.2014.01.036

Polyhedron 72 (2014) 140–146
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
The first nickel(II) complexes of disubstituted
diphenyldithiophosphates: Synthesis, spectroscopic, electrochemical,
antifungal and single crystal X-ray analysis
Sandeep Kumar a, Ruchi Khajuria a, Vivek K. Gupta b, Rajni Kant b, Sushil K. Pandey a,
⇑
a Department of Chemistry, University of Jammu, Jammu 180006, J & K, India
b X-ray Crystallographic Laboratory, Department of Physics and Electronics, University of Jammu, Jammu 180006, J & K, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Five novel nickel(II) complexes of disubstituted diphenyldithiophosphates, [{(ArO)2PS2}2Ni] [Ar = 2,4-
(CH3)2C6H3 (1), 2,5-(CH3)2C6H3 (2), 3,4-(CH3)2C6H3 (3), 3,5-(CH3)2C6H3 (4) and 4-Cl-3-CH3C6H3 (5)], have
been synthesized in aqueous medium and structurally characterized by IR, heteronuclear NMR (1H, 13C
and 31P) spectroscopic and single crystal X-ray analyses. Complexes 1 and 5 crystallize in the triclinic
Received 14 November 2013
Accepted 27 January 2014
Available online 12 February 2014
ꢀ
space group P1, whereas complex 4 crystallizes in the monoclinic space group P21/n. In these complexes,
Keywords:
the ligands are coordinated to the nickel ion as a bidentate chelating agent via the two thiolate sulfur
atoms, leading to a spirocyclic system. Crystal structure determination of complexes 1, 4 and 5 reveals
that the complexes consist of mononuclear units with the nickel(II) ion coordinated in a bis-bidentate
fashion with a distorted square planar coordination environment. A cyclic voltammetry experiment
was used to probe the redox capabilities of complex 4. The investigated complexes, along with the
ligands, have been screened for in vitro antifungal activities against the fungus Penicillium chrysogenum.
Ó 2014 Elsevier Ltd. All rights reserved.
Diphenyldithiophosphate
Cyclic voltammetry
Single crystal X-ray
Antifungal
1. Introduction
These ligands exhibit versatile modesof coordinationand are known
to exist in bidentate and monodentate forms. However, nickel com-
Nickel sulfur chemistry has received considerable attention as
nickel compounds have proved to be potentially important in a
diverse number of technical applications, such as paramagnetic
antiferromagnetic phase-changing materials [1] and hydrodesulfu-
rization catalysts [2]. Their electrochemical applications have been
well established, which include electrochemical activation of freons
[3]. The unique morphologies of nickel sulfides have encouraged the
preparation of nanomaterials and their data storage ability has been
employed in the production of various nanowires [4]. Nickel
sorbents have been investigated for their capability to remove sulfur
compounds in soil and coal gas [5]. On a biological front, they are key
components of natural hydrogenase and are active promoters in
current hydrotreating catalysts [6]. Nickel thiolate complexes have
received special attention in recent years because sulfur-ligated
nickel complexes mimic the [Fe–Ni]-hydrogenase active site and
dimeric metal complexes based on nickel thiolate hydrides have
been shown to be catalytically active for proton reduction [7]. Nickel
complexes with O,O0-dialkyl/alkylene dithiophosphates have
consistently retained interest over the last few decades [8–11].
plexes with the analogous aromatic ligands have been less studied
[12,13]. A survey of the literature confirms the importance of nickel
complexes with thio ligands, where the main thrust of research has
been on the preparation of complexes having varied applications in
agriculture as pesticides [14], in lubrication engineering as antiwear
and extreme pressure additives [15,16], in industry as antioxidants
of polyolefines [17] and as catalyst stabilizers [18]. In continuation
of our work on dithiophosphates [19–21], we report herein for the
first time the synthesis, spectroscopic, electrochemical, antifungal
and single crystal X-ray analysis of nickel(II) diphenyldithiophos-
phate complexes having disubstituted phenyl rings.
2. Experimental
2.1. Materials and instrumentation
All chemicals and solvents used in this study were of high purity.
Solvents were distilled and dried using standard methods before
use. Chloroform (Thomas Baker, b.p. 61 °C) was dried over P2O5.
All the disubstituted phenols were procured from Sigma Aldrich
and used without purification. The sodium salts of disubstituted
⇑
Corresponding author. Tel.: +91 9419147679.
E-mail address: kpsushil@rediffmail.com (S.K. Pandey).
O,O0-diphenyldithiophosphates,
i.e.
{(2,4-CH3)2C6H3O}2PS2Na,
http://dx.doi.org/10.1016/j.poly.2014.01.036
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

S. Kumar et al. / Polyhedron 72 (2014) 140–146
141
{(2,5-CH3)2C6H3O}2PS2Na, {(3,4-CH3)2C6H3O}2PS2Na, {(3,5-CH3)2
C6H3O}2PS2Na and (4-Cl-3-CH3C6H3O)2PS2Na, were synthesized
according to a literature procedure for tolyldithiophosphates [21].
Moisture was carefully excluded for the synthesis of the ligands
throughout the experimental manipulations using standard
Schlenk techniques. Nickel was estimated gravimetrically as
nickel(II)dimethylglyoximate. Chlorine was estimated by Volhard’s
method [22]. Elemental analyses (C, H, N and S) were conducted
using an Elemental Analyser Vario EL-III (Indian Institute of Integra-
tive Medicine, Jammu). Infrared spectra were recorded in the range
4000–200 cmꢀ1 on a Perkin Elmer-spectrum RX1 FT-IR spectropho-
tometer (SAIF, Panjab University, Chandigarh). The 1H and 13C NMR
spectra were recorded in CDCl3 using TMS as an internal reference.
The 31P NMR spectra were recorded in CDCl3 using H3PO4 (85%) as
an external reference on a Bruker Avance III 400 MHz (Department
of Chemistry, University of Jammu, Jammu). All chemical shifts are
reported in d units downfield from TMS = d 0 ppm. The cyclic vol-
tammogram was recorded on an Autolabs (Department of Chemis-
try, University of Jammu, Jammu). The potential was applied
between the reference electrode (Ag/AgCl) and the working elec-
trode (gold electrode) and the current was measured between the
working electrode and the counter electrode (platinum wire).
0.1 M phosphate buffer solution (pH 7.0) was used. For antifungal
studies, the fungus Penicillium chrysogenum was procured from
the Department of Botany, University of Jammu, Jammu. All the
glasswares and materials used for the antifungal activity measure-
ments were sterilized in an autoclave.
{(3,4-CH3)2C6H3O}2PS2Na (1.00 g, 2.77 mmol). The resulting solid
was recrystallized from a chloroform/n-hexane mixture (3:1) at
room temperature. Yield: 0.90 g (90%); M.p. 169–171 °C (dec);
Anal. Calc. for C32H36O4P2S4Ni: C, 52.40; H, 4.95; S, 17.49; Ni,
8.00; Found: C, 52.33; H, 4.89; S, 17.46; Ni, 7.86%; IR (KBr,
cmꢀ1): 1088 s [
573 m [
PꢀS]sym, 368 w [
m
(P)ꢀOꢀC], 861 s [
m
PꢀOꢀ(C)], 653 s [
m
PꢀS]asym
,
m
m
NiꢀS]; 1H NMR (CDCl3, ppm): 2.29
(s, 12H, 4–CH3), 2.31 (s, 12H, 3–CH3), 7.16 (d, J = 7.6 Hz, 4H, H6),
7.28 (s, 4H, H2), 7.40 (d, J = 8 Hz, 4H, H5); 13C NMR (CDCl3, ppm):
19.2 (4–CH3), 19.9 (3–CH3), 118.3 (C6), 122.2 (C2), 130.4 (C4–
CH3), 134.4 (C5), 138.2 (C3–CH3), 147.8 (C1–O); 31P NMR (CDCl3,
ppm): 86.0 (s).
2.2.4. Synthesis of [{3,5-(CH3)2C6H3O}2PS2]2Ni (4)
Complex 4 was prepared by a similar procedure as described for
complex 1, using Ni(NO3)2ꢁ6H2O (0.40 g, 1.37 mmol) and {(3,5-
CH3)2C6H3O}2PS2Na (1.00 g, 2.77 mmol). The resulting solid was
recrystallized from a chloroform/n-hexane mixture (3:1) at room
temperature. Yield: 0.92 g (92%); M.p. 187–189 °C (dec); Anal. Calc.
for C32H36O4P2S4Ni: C, 52.40; H, 4.95; S, 17.49; Ni, 8.00; Found: C,
52.32; H, 4.81; S, 17.43; Ni, 7.92%; IR (KBr, cmꢀ1): 1101 s
[
m
(P)ꢀOꢀC], 858 s [
m
PꢀOꢀ(C)], 654 s [
m
PꢀS]asym, 557 m [
m
PꢀS]sym
,
371 w [
m
NiꢀS]; 1H NMR (CDCl3, ppm): 2.35 (s, 24H, 3,5–(CH3)2),
6.80 (s, 8H, H2,6), 7.08 (s, 4H, H4); 13C NMR (CDCl3, ppm): 21.3
(3,5–(CH3)2), 118.9 (C2,6), 127.7 (C4), 139.5 (C3,5–CH3), 149.6 (C1–
O); 31P NMR (CDCl3, ppm): 84.9 (s).
2.2.5. Synthesis of [(4-Cl-3-CH3C6H3O)2PS2]2Ni (5)
2.2. Synthesis of complexes 1–5
Complex 5 was prepared by a similar procedure as described for
complex 1, using Ni(NO3)2ꢁ6H2O (0.36 g, 1.24 mmol) and (4-Cl-3-
CH3C6H3O)2PS2Na (1.00 g, 2.49 mmol). The resulting solid was
recrystallized from a chloroform/n-hexane mixture (3:1) at room
temperature. Yield: 0.90 g (90%); M.p. 144–146 °C (dec); Anal. Calc.
for C28H24O4P2S4Cl4Ni: C, 41.25; H, 2.97; S, 15.73; Cl, 17.40; Ni,
7.20; Found: C, 41.16; H, 2.75; S, 15.54; Cl, 17.36; Ni, 7.09%; IR
2.2.1. Synthesis of [{2,4-(CH3)2C6H3O}2PS2]2Ni (1)
To
a
stirred aqueous solution of Ni(NO3)2ꢁ6H2O (0.40 g,
1.37 mmol), an aqueous solution of {(2,4-CH3)2C6H3O}2PS2Na
(1.00 g, 2.77 mmol) was added in a 1:2 M ratio with constant stir-
ring. A solid precipitated immediately. After 30 min of stirring, the
reaction contents were filtered to obtain the complex [{(2,4-CH3)2
C6H3O}2PS2]2Ni (1) as a purple powdery solid. The complex was
recrystallized from chloroform/n-hexane mixture (3:1) at room
temperature. Yield: 0.91 g (91%); M.p. 172–174 °C (dec); Anal. Calc.
for C32H36O4P2S4Ni: C, 52.40; H, 4.95; S, 17.49; Ni, 8.00; Found: C,
52.35; H, 4.71; S, 17.47; Ni, 7.91%; IR (KBr, cmꢀ1): 1105 s
(KBr, cmꢀ1): 1157
PꢀS]asym, 635 m [
s
[
m
(P)ꢀOꢀC], 971
s
[
m
PꢀOꢀ(C)], 704
s
[m
m
PꢀS]sym, 381 w [
m
NiꢀS]; 1H NMR (CDCl3,
ppm): 2.27 (s, 24H, 3–CH3), 7.13 (d, J = 8 Hz, 4H, H6), 7.18 (s, 4H,
H2), 7.31 (d, J = 8.8 Hz, 4H, H3); 13C NMR (CDCl3, ppm): 19.7 (3–
CH3), 120.6 (C6), 123.9 (C2), 127.1 (C4–Cl), 128.7 (C5–CH3), 135.4
(C3), 151.3 (C1–O); 31P NMR (CDCl3, ppm): 86.1 (s).
[
m
(P)ꢀOꢀC], 869 s [
m
PꢀOꢀ(C)], 650 s [
m
PꢀS]asym, 572 m [
m
PꢀS]sym
,
370 w [
m
NiꢀS]; 1H NMR (CDCl3, ppm): 2.30 (s, 12H, 2–CH3), 2.36 (s,
All the complexes 1–5 were obtained as purple solids.
12H, 4–CH3), 6.87 (d, J = 8 Hz, 4H, H6), 7.07 (d, J = 8 Hz, 4H, H5), 7.37
(s, 4H, H3); 13C NMR (CDCl3, ppm): 17.3 (2–CH3), 20.8 (4–CH3),
120.8 (C6), 127.4 (C2–CH3), 129.9 (C5), 132.1 (C4–CH3), 135.4 (C3),
146.8 (C1–O); 31P NMR (CDCl3, ppm): 85.8 (s).
R4
R5
C5 C6
C4 C1
C3 C2
R3
O
2.2.2. Synthesis of [{2,5-(CH3)2C6H3O}2PS2]2Ni (2)
Complex 2 was prepared by a similar procedure as described for
complex 1, using Ni(NO3)2ꢁ6H2O (0.40 g, 1.37 mmol) and {(2,5-
CH3)2C6H3O}2PS2Na (1.00 g, 2.77 mmol). The resulting solid was
recrystallized from a chloroform/n-hexane mixture (3:1) at room
temperature. Yield: 0.89 g (89%); M.p. 180–182 °C (dec); Anal. Calc.
for C32H36O4P2S4Ni: C, 52.40; H, 4.95; S, 17.49; Ni, 8.00; Found: C,
52.36; H, 4.91; S, 17.42; Ni, 7.78%; IR (KBr, cmꢀ1): 1099 s
R1
R2
1. R1 = CH3, R2 = H3, R3 = CH3, R4 = H5, R5 = H6
2. R1 = CH3, R2 = H3, R3 = H4, R4 = CH3, R5 = H6
3. R1 = H2, R2 = CH3, R3 = CH3, R4 = H5, R5 = H6
4. R1 = H2, R2 = CH3, R3 = H4, R4 = CH3, R5 = H6
5. R1 = H2, R2 = CH3, R3 = Cl, R4 = H5, R5 = H6
[
m
(P)ꢀOꢀC], 876 s [
m
PꢀOꢀ(C)], 653 s [
m
PꢀS]asym, 578 m [
m
PꢀS]sym
,
372 w [
m
NiꢀS]; 1H NMR (CDCl3, ppm): 2.25 (s, 12H, 2–CH3), 2.34 (s,
Scheme 1. Ring labelling for NMR spectroscopic assignments of complexes 1–5.
12H, 5–CH3), 6.98 (d, J = 7.6 Hz, 4H, H3), 7.12 (d, J = 7.6 Hz, 4H, H4),
7.25 (s, 4H, H6); 13C NMR (CDCl3, ppm): 16.6 (2–CH3), 21.0 (5–CH3),
121.6 (C6), 126.1 (C4), 127.0 (C2–CH3), 131.1 (C3), 136.9 (C5–CH3),
149.4 (C1–O); 31P NMR (CDCl3, ppm): 84.8 (s).
2.3. Crystallography data collection and refinement
2.2.3. Synthesis of [{3,4-(CH3)2C6H3O}2PS2]2Ni (3)
Complex 3 was prepared by a similar procedure as described for
complex 1, using Ni(NO3)2ꢁ6H2O (0.40 g, 1.37 mmol) and
Crystallization of complexes 1, 4 and 5 was executed by very
slow evaporation of their saturated solutions in a chloroform/n-
hexane mixture (3:1) at room temperature, yielding suitable single

142
S. Kumar et al. / Polyhedron 72 (2014) 140–146
Table 1
Summary of the crystal structure, data collection and structure refinement parameters for complexes 1, 4 and 5.
Complex
1
4
5
Crystal system
Space group
Temperature, K
Empirical formula
Z
triclinic
P1
293(2)
monoclinic
P21/n
293(2)
C32H36NiO4P2S4
2
triclinic
P1
293(2)
C28H24Cl4NiO4P2S4
1
ꢀ
ꢀ
C32H36NiO4P2S4
1
Formula weight
a (Å)
b (Å)
733.50
733.50
815.16
8.213(5)
9.317(5)
11.803(5)
89.779(5)
76.444(5)
80.267(5)
864.8(8)
1.408
13.4218(3)
9.3238(2)
13.8970(3)
90.00
94.352(2)
90.00
7.1994(3)
9.6421(3)
13.0181(4)
87.660(3)
76.108(3)
74.335(3)
844.39(5)
1.603
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
1734.09(7)
1.405
Dcalc (g/cm3)
F(000)
382
764
414
h range for data collection (°)
No. of collected reflections
No. of independent reflections
Rint
3.47–26.00
3400
2429
3.66–25.99
3408
2864
3.75–26.00
3303
2904
0.0308
0.0490
0.0305
No. of data/restraints/parameters
R1, wR2 [I > 2r(I)]
3400/0/200
0.0385, 0.0810
0.0624, 0.0913
0.986
3408/0/200
0.0336, 0.0832
0.0435, 0.0907
1.063
3303/0/198
0.0270, 0.0649
0.0328, 0.0684
1.031
R1, wR2 (all data)
Goodness-of-fit on F2
Largest difference in peak/hole, (e Åꢀ3
)
0.309/ꢀ0.355
0.293/ꢀ0.358
0.324/ꢀ0.283
crystals for X-ray analysis. The structures of complexes 1, 4 and 5
were determined by single crystal X-ray diffraction analysis. X-ray
data of the complexes were collected on an X’calibur-Oxford Dif-
fraction single crystal diffractometer with a CCD area-detector
complexes were found to be soluble in all common organic
solvents.
3.1. IR spectra
(graphite-monochromator, Mo K
a radiation, k = 0.71073 Å). Data
were corrected for Lorentz, polarization and absorption factors.
The structures were solved by direct methods using SHELXS97 [23].
All non-H atoms of the molecules were located in the best E-
map. Full-matrix least-squares refinement was carried out using
SHELXL97 [23]. The geometry of the molecules were calculated using
WinGX [24], PARST [25] and PLATON [26]. Atomic scattering factors
were taken from the International Tables for X-ray Crystallography
(1992, Vol. C, Tables 4.2.6.8 and 6.1.1.4). Molecular drawings were
obtained using DIAMOND version 2.1 [27]. Crystallographic data and
details of the data collection and structure solution and refine-
ments are listed in Table 1.
The IR spectra of complexes 1–5 were recorded in the range
4000–200 cmꢀ1 as KBr pellets and tentative assignments were
made on the basis of relevant literature reports [11–13,21]. A com-
parison of the IR spectra of the complexes with the starting mate-
rials has also shown significant characteristic changes and shifting
of the bands. Two strong intensity bands were observed in the re-
gions 1157–1086 and 971–858 cmꢀ1, which may be ascribed to the
[
m
(P)ꢀOꢀC] and [
m
PꢀOꢀ(C)] vibrations of the diphenyldithiophos-
phate moiety, respectively. The bands for [
m
PꢀS]asym and [ PꢀS]sym
m
of the diphenyldithiophosphate moiety were observed in the re-
gions 704–653 and 635–557 cmꢀ1, respectively. The appearance
of a new band for [
m
NiꢀS] in the region 381–368 cmꢀ1 [13] in
2.4. Antifungal studies
the spectra of these complexes is also indicative of the formation
of a nickel–sulfur bond.
An antifungal activity assay was carried out by the agar well dif-
fusion method [28]. With a sterile cork borer of size 6 mm, 48 h old
cultures grown on potato dextrose agar (PDA) were used for pre-
paring the spore suspension for inoculation. 0.1 mL of the test fun-
gal spore suspension was spread on sterile agar plates. Appropriate
3.2. 1H NMR
The 1H NMR spectral data of complexes 1–5 show the charac-
teristic proton resonances of the corresponding substituted phenyl
protons. The splitting patterns of the peaks in the spectra of all the
complexes were found to be consistent with the structures. The
chemical shifts of the methyl (ꢀCH3) protons of the phenyl rings
were observed as a singlet in the region 2.25–2.36 ppm. The aro-
matic protons of the phenyl groups were observed in the region
6.80–7.40 ppm with their characteristic splitting patterns. Three
resonances were observed for the phenyl protons in complexes
1–3 and 5, whereas complex 4 exhibited two resonances for the
phenyl protons (Scheme 1).
wells were made on the agar plate using the cork borer and 50 lL
of test oil and fungicide of different concentrations were loaded.
Plates were kept for pre-incubation for 30 min in a refrigerator
and then were incubated for 48 h at 27 °C. The antifungal activity
was evaluated by measuring the zone of inhibition of fungal
growth surrounding the well with the sample solution in DMSO.
The experiment was carried out in triplicate.
3. Results and discussion
The reactions of nickel(II) nitrate hexahydrate with sodium
O,O0-bis(disubstitutedphenyl)phosphorodithioate in a 1:2 stoichi-
ometric ratio were quite facile at room temperature and yielded
the nickel(II) diphenydithiophosphates, formulated as [{(ArO)2
PS2}2Ni] [Ar = 2,4-(CH3)2C6H3 (1), 2,5-(CH3)2C6H3 (2), 3,4-(CH3)2
C6H3 (3), 3,5-(CH3)2C6H3 (4) and 4-Cl-3-CH3C6H3 (5)] according
to Scheme 2. The precipitated purple solid complexes were
separated by filtration and repeatedly washed with water. These
3.3. 13C NMR
The 13C NMR spectra (CDCl3) of complexes 1–5 showed that the
chemical shifts due to the carbon atoms of the phenyl rings were
retained with a marginal shift in their values compared to the
parent ligands. The chemical shifts for the methyl (–CH3) carbons
attached to the phenyl rings were found in the region

S. Kumar et al. / Polyhedron 72 (2014) 140–146
143
H2O
[{(ArO)2PS2}2Ni]
2(ArO)2PS2Na
+
Ni(NO3)2.6H2O
Stirring~30min
-2NaNO3
(1-5)
Ar = 2,4-(CH3)2C6H3 (1), 2,5-(CH3)2C6H3 (2), 3,4-(CH3)2C6H3 (3), 3,5-(CH3)2C6H3 (4) and 4-Cl-3-CH3C6H3 (5)
Scheme 2. Preparation of complexes 1–5.
16.6–21.3 ppm. The carbon nuclei of the aryl groups displayed
their resonances in the region 118.3–135.4 ppm. The chemical
shifts for CꢀO carbon nuclei were found in the region 146.8–
151.3 ppm. The chemical shifts for the Cꢀ(CH3) carbon nuclei were
observed in the region 127.0–139.5 ppm.
3.4. 31P NMR
31P NMR spectra of complexes 1–5 (proton-decoupled) showed
the chemical shifts as a singlet in each case in the upfield region
compared to the parent ligands (106.5–107.4 ppm), with a differ-
ence of 21–23 ppm. The phosphorus atom of the diphenyldithio-
phosphate moiety in the complexes shows one signal in the
region 84.8–86.1 ppm, which is consistent with the bidentate
behavior of the dithiophosphate moiety [29].
3.5. Crystal and molecular structures of complexes 1, 4 and 5
The X-ray diffraction analysis of complexes 1, 4 and 5 reveals a
monomeric distorted square planar geometry around the nickel
centres (Figs. 1–3). Complexes 1 and 5 crystallize in the triclinic
Fig. 2. Molecular structure of [{3,5-(CH3)2C6H3O}2PS2]2Ni (4) with displacement
ellipsoids drawn at the 50% probability level.
ꢀ
space group P1, whereas complex 4 crystallizes in the monoclinic
space group P21/n. The nickel atom is four coordinated by four sul-
fur atoms from two acyclic dithiophosphato ligands bonded in
bidentate chelating fashion to form a spirocyclic ring. A selection
of the bonds lengths and angles for complexes 1, 4 and 5 are given
in Table 2. The Ni–S1 and Ni–S2 bond distances are 2.229(11) and
2.229(11) Å for complex 1, 2.2305(6) and 2.2370(6) Å for complex
4
and 2.2396(5) and 2.2438(5) Å for complex 5, which are
comparable to the values observed in the square-planar complex
Fig. 3. Molecular structure of [(4-Cl-3-CH3C6H3O)2PS2]2Ni (5) with displacement
ellipsoids drawn at the 50% probability level.
Ni[S2P(OC6H4CH3-o)2]2 (2.2415(6) and 2.2241(6) Å) [12]. These
bond lengths are also comparable to bond lengths of dialkyl dithio-
phosphate analogues reported in the literature, such as Ni
[S2P(OBui)2]2 (2.2244(5) and 2.2278(5) Å) [11], Ni[S2P(OEt)2]2
(2.230 and 2.236 Å) [30] and Ni[S2P(OPri)2]2 (2.227(1) and
2.216(1) Å) [31]. The P1–S1 bond distances are 1.984(13),
1.9778(8) and 1.9723(7) Å in complexes 1, 4 and 5, while the P1–
S2 bond distances are 1.984(12), 1.9770(8) and 1.9776(7) Å,
respectively. These bond distances are analogous to the values ob-
served in Ni[S2P(OC6H4CH3-o)2]2 (1.9839(7) and 1.9850(7) Å) and
Ni[S2P(OC6H4CH3-m)2]2 (1.9884(8) and 1.9778(8) Å) [12]. In the
ditolyldithiophosphate derivative Ni[S2P(OC6H4Me-o)2]2 C14H12N2
C6H6 [13], the chelation of one of the dithiophosphato ligands is
defined as (aniso)bidentate, in which the P1–S1 and P1–S2 bond
Fig. 1. Molecular structure of [{2,4-(CH3)2C6H3O}2PS2]2Ni (1) with displacement
ellipsoids drawn at the 50% probability level.

144
S. Kumar et al. / Polyhedron 72 (2014) 140–146
Table 2
involves a one step process with a reduction cathodic peak for
Selected bonds lengths (Å) and angles (°) for complexes 1, 4 and 5.a
the Ni(II)/Ni(I) couple at Epc = ꢀ0.27176 V and with a peak current
I
pc = 1.45 ꢂ 10ꢀ7 A. On the anodic side, the direct oxidation of Ni(I)/
1
Ni1–S1
Ni1–S2
S1–P1
S2–P1
P1–O1
2.229(11)
2.229(11)
1.984(13)
1.984(12)
1.583(18)
1.580(2)
S1–Ni1–S2i
S1–Ni1–S2
S1–P1–S2
S1–P1–O1
S1–P1–O2
S2–P1–O1
S2–P1–O2
O1–P1–O2
91.96(4)
88.04(4)
Ni(II) is observed at Epa = 0.62912 V and the peak current is
I
pa = 1.60 ꢂ 10ꢀ7 A. The difference between the cathodic and ano-
102.65(5)
115.52(9)
115.74(9)
115.21(8)
115.73(9)
92.85(10)
dic potentials (
D
Ep) is ꢀ90 V. This couple is found to be quasi-
reversible and the ratio of cathodic to anodic peak currents (Ipc
/
P1–O2
Ipa = 0.90) corresponds to a simple one-electron process. The E1/2
S1–Ni1–S1i
S2–Ni1–S2i
180.00(4)
180.00(4)
value of the complex is +0.17 V.
4
Ni1–S1
Ni1–S2
P1–S1
2.2305(6)
S1ii–Ni1–S2
S1–Ni1–S2
O1–P1–S1
O2–P1–S1
O1–P1–S2ii
O2–P1–S2ii
S2ii–P1–S1
O2–P1–O1
88.79(2)
91.21(2)
3.7. Antifungal studies
2.2370(6)
1.9778(8)
1.9770(8)
1.5880(18)
1.5813(17)
114.20(8)
114.19(7)
115.02(7)
109.98(7)
104.43(4)
99.34(9)
Sulfur containing compounds are well known to exhibit anti-
fungal activity [36]. Keeping this in view, the antifungal activities
of the ligands and the representative metal complexes 1, 4 and 5
have been measured against P. chrysogenum. The antifungal
screening data (Table 3) establishes a linear relationship between
concentration and zone of inhibition (in cm). On enhancing the
concentration of the complex, the inhibition zone increases, i.e.
all the complexes inhibited the growth of the fungus significantly.
The ligands {(2,4-CH3)2C6H3O}2PS2Na (L1) and {(3,5-CH3)2C6H3O}2
PS2Na (L2) showed a negligible inhibitory effect compared to the
ligand (4-Cl-3-CH3C6H3O)2PS2Na (L3) and complexes 1, 4 and 5.
This increase in activity of ligand L3 may be due to the presence
of a chloro group on the phenyl ring. Generally, the nature (elec-
tron withdrawing or electron releasing substituents) and position
of the substituents present on the phenyl ring decide the antimi-
crobial activities. It is obvious that the inhibitory action becomes
enhanced with the introduction of the electron-withdrawing
chloro group on the phenyl ring [37]. Complexes 1, 4 and 5 exhibit
higher antifungal activities than the corresponding free ligands L1,
L2 and L3 due to the chelation of the ligands with the nickel metal
ion. It also reveals that an enhanced inhibitory effect of complex 5
is not only pertaining to the ligand L3, but chelation of the ligand
with the nickel metal ion is also a liable factor. The increase in anti-
fungal activity might be due to faster diffusion of the complexes as
a whole through the cell membrane, or due to a combined activity
effect of the metal and the ligand. The polarity of the metal ion will
be reduced to a greater extent due to the overlap of the ligand
orbitals and partial sharing of the positive charge of the metal
ion with the donor group [38]. Further, it increases the delocaliza-
P1–S2
P1–O1
P1–O2
S1–Ni1–S1ii
S2–Ni1–S2ii
180.00(3)
180.00(18)
5
Ni2–S1
Ni2–S2
S1–P1
2.2396(5)
2.2438(5)
1.9723(7)
1.9776(7)
1.5855(14)
1.5917(14)
180.00(2)
180.00(2)
S1–Ni2–S2
S1–Ni2–S2ii
O1–P1–O2
S2–P1–O2
S2–P1–O1
S1–P1–O2
S1–P1–O1
S1–P1–S2
89.142(18)
90.86(18)
98.78(8)
113.95(6)
115.38(6)
114.37(6)
108.91(6)
105.61(3)
S2–P1
P1–O1
P1–O2
S1–Ni2–S1ii
S2–Ni2–S2ii
a
Symmetry transformations used to generate equivalent atoms: (i) ꢀx, ꢀy, ꢀz,
(ii) 1 ꢀ x, ꢀy, ꢀz.
lengths are 1.997(2) and 1.969(2) Å, whereas the other dith-
iophosphato ligand is bonded in a monodentate fashion, for which
the P2–S3 and P2–S4 bond distances are 1.995(2) and 1.941(2) Å.
The phosphorus-sulfur bond lengths in complexes 1, 4 and 5 fall
between the bond lengths of P–S and P@S bonds, since the
phosphorus-sulfur bond distances of complexes 1, 4 and 5 are mar-
ginally shorter than the single P–S bonds found in [Ni(S2P{O}OCH2
CH2Ph)(dppe)] (2.042(2) and 2.038(2) Å) [32] and larger than the
P@S bond observed in HS2POCMe2CMe2O (1.923(2) Å) [33].
The S1–Ni–S2 bond angles of complexes 1, 4 and 5 are found to
be 88.04(4)°, 88.79(2)° and 89.142(18)°, respectively, which are
typical of square planar complexes, such as Ni[S2P(OBui)2]2
(88.389(16)°) [11], Ni[S2P(OC6H4CH3-o)2]2 (88.39(2)°) [12],
Ni[S2P(OC6H4Me-p)2]2 (89.12(2)°) [34], Ni[S2P(OEt)2]2 (88.5°) and
Ni[S2P(OPri)2]2 (88.10(4)°). However, these bite angles are reduced
to 82.05(4)° and 81.33(2)° in the adducts Ni[S2P(OC6H4Me-o)2]2
C14H12N2 C6H6 [13] and Ni[S2P(OC6H4Me-p)2]2 C10H8N [13],
respectively. The distortion in the bond angles is obviously caused
by the presence of the donor atom. The S1–P1–S2 bond angle for
complex 1 is 102.65(5)°, which is akin to the values observed in
Ni[S2P(OCH2Ph)2]2 (102.81(4)°) [12] and [Ni(S2P{OC2H5}2)2]
(102.58(3)°) [35]. In complexes 4 and 5, the S1–P1–S2 bond angles
[104.43(4)° and 105.61(3)°] are quite analogous to the value found
for Ni[S2P(OC6H4CH3-m)2]2 (104.18(4)°) [12]. So, a comparison of
the data reveals that there are no significant changes in the bond
distances and bond angles in alkyl-, tolyl- and diphenyl-dithio-
phosphate derivatives. The marginal difference in the values of
the bond distances and angles may be attributed to the presence
of a phenyl ring and any substitution on it.
tion of
p-electrons over the whole chelate ring and enhances the
3.6. Electrochemical behavior
The redox behavior of complex 4 in MeOH solution has been
studied by cyclic voltammetry (Fig. 4). It clearly reveals that the
redox process of the nickel(II) complex at the scan rate 100 mV/s
Fig. 4. Cyclic voltammetric curve of the complex [{3,5-(CH3)2C6H3O}2PS2]2Ni (4).

S. Kumar et al. / Polyhedron 72 (2014) 140–146
145
Table 3
Antifungal activity of the ligands and complexes against the fungus Penicillium chrysogenum.
Ligand/complex
Concentration (ppm)
Zone of Inhibition (in cm)
{(2,4-CH3)2C6H3O}2PS2Na (L1)
100
500
1000
100
500
1000
100
500
1000
100
500
1000
100
0.0
0.0
0.0
0.0
0.0
0.0
0.5
0.7
1.0
0.4
0.6
0.8
0.4
0.5
0.7
0.8
0.9
1.2
{(3,5-CH3)2C6H3O}2PS2Na (L2)
(4-Cl-3-CH3C6H3O)2PS2Na (L3)
[{(2,4-CH3)2C6H3O}2PS2]2Ni (1)
[{(3,5-CH3)2C6H3O}2PS2]2Ni (4)
[{4-Cl-3-CH3C6H3O}2PS2]2Ni (5)
500
1000
100
500
1000
Fig. 5. Comparative results of antifungal screening data.
lipophilicity of the complexes, which enhances the penetration of
the complexes into the lipid membranes and blocking of the metal
binding sites in the enzymes of microorganisms, that restricts fur-
ther growth of the organism. The fungal growth inhibition capacity
of the complexes followed the order: 5 > 1 > 4. The illustrated com-
parative results of antifungal analysis are given in Fig. 5.
Acknowledgments
The authors are grateful to the NMR laboratory Department of
Chemistry, University of Jammu, Jammu for providing NMR spec-
tral facilities (PURSE program). One of the authors (Rajni Kant)
acknowledges the DST for the single crystal X-ray diffractometer
as a National Facility under Project No. SR/S2/CMP-47/2003.
4. Conclusion
Appendix A. Supplementary material
We have reported the synthesis and characterization of some
novel nickel(II) diphenyldithiophosphate complexes for the first
time using a disubstituted phenyl ring having methyl and chlorine
substituents. The results of the single crystal X-ray structure anal-
ysis establish the structural aspects of the new complexes. The ele-
mental analysis, IR and NMR (1H, 13C and 31P) results have been
envisaged, on the basis of which a distorted square planar coordi-
nation environment is assigned around the nickel atom. Further, an
electrochemical study depicted that the redox process is quasi-
reversible and corresponds to a simple one-electron process. The
antifungal screening of these complexes has indicated potential
growth inhibition capacity in the order: 5 > 1 > 4. The results are
quite promising; hence these complexes are candidates for explo-
ration as specific antifungal drugs due to their decent activity
against P. chrysogenum.
CCDC 960922, 967391 and 967392 contain the supplementary
crystallographic data for complexes 1, 4 and 5. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk.
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