Synthesis and spectral studies on NiS4, NiS2PN, NiS2P2 chromophores: Single-crystal X-ray structure of [Ni(dbpdtc)2] (dbpdtc = benzyl(4-(benzylamino)phenyl)dithiocarbamate)

Article abstract of DOI:10.1007/s11243-010-9398-2

Three complexes of a dithiocarbamate ligand (dbpdtc = benzyl(4- (benzylamino)phenyl)dithiocarbamate), namely [Ni(dbpdtc)₂] (1), [Ni(dbpdtc)(NCS)(PPh₃)] (2) and [Ni(dbpdtc)(PPh₃) ₂]ClO₄ (3) have been prepared. The complexes were characterized by IR, electronic spectroscopy and cyclic voltammetry. A single-crystal X-ray structural analysis was carried out for complex 1 and showed that the nickel is in a distorted square planar environment with a NiS₄ chromophore. For the two mixed ligand complexes, the thioureide ν _C-N values were shifted to higher wavenumbers compared to [Ni(dbpdtc)₂], suggesting increased strength of the thioureide bond due to the presence of the π-accepting phosphine. Electronic spectral studies suggest square planar geometries for the complexes. Cyclic voltammetry showed easier reduction of nickel(II) to nickel(I) in the mixed ligand complexes compared to [Ni(dbpdtc)₂].

Full text of DOI:10.1007/s11243-010-9398-2

Transition Met Chem (2010) 35:815–819
DOI 10.1007/s11243-010-9398-2
Synthesis and spectral studies on NiS , NiS PN, NiS P
2 2
4
2
chromophores: Single-crystal X-ray structure of [Ni(dbpdtc)2]
dbpdtc 5 benzyl(4-(benzylamino)phenyl)dithiocarbamate)
(
Narayanaswamy Srinivasan
Panneerselvam Valarmathi
•
•
Subbiah Thirumaran Samuele Ciattini
•
Received: 23 March 2010 / Accepted: 2 July 2010 / Published online: 16 July 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Three complexes of a dithiocarbamate ligand
dbpdtc = benzyl(4-(benzylamino)phenyl)dithiocarbamate),
namely [Ni(dbpdtc) ] (1), [Ni(dbpdtc)(NCS)(PPh )] (2)
their anticancer activity [3]. Dithiocarbamate ligands display
(
a strong propensity of binding to metal atoms such as nickel
[1]. Divalent nickel complexes of dithiocarbamates with
different substituents contain the planar diamagnetic NiS4
chromophore [4, 5]. Ni(II) dithiocarbamates are borderline
acceptors, and they can react with Lewis bases such as
phosphines as well as hard bases such as nitrogenous ligands
[6, 7]. The synergically induced softness and the electronic
effect of their substituents on the dithiocarbamate ligands
were found to be important in determining their reactivities
[8, 9]. The effect of alkyl substituents in the metal dithio-
carbamates has been investigated earlier [10]. The aim of the
present work was to prepare a Ni(II) complex of benzyl
(4-(benzylamino)phenyl)dithiocarbamate and to investigate
2
3
and [Ni(dbpdtc)(PPh ) ]ClO (3) have been prepared. The
2
3
4
complexes were characterized by IR, electronic spectros-
copy and cyclic voltammetry. A single-crystal X-ray
structural analysis was carried out for complex 1 and
showed that the nickel is in a distorted square planar
environment with a NiS chromophore. For the two mixed
4
ligand complexes, the thioureide mC–N values were shifted
to higher wavenumbers compared to [Ni(dbpdtc) ], sug-
2
gesting increased strength of the thioureide bond due to the
presence of the p-accepting phosphine. Electronic spectral
studies suggest square planar geometries for the com-
plexes. Cyclic voltammetry showed easier reduction of
nickel(II) to nickel(I) in the mixed ligand complexes
compared to [Ni(dbpdtc)2].
the reactivity of this complex towards PPh . In this paper, we
3
report the synthesis and spectral studies of complexes 1–3,
along with the single-crystal X-ray structure of 1.
Introduction
Experimental
Dithiocarbamato complexes of transition metals continue to
attract the attention of researchers [1, 2]. Dithiocarbamates
are used in analytical determinations, as pharmaceuticals, as
pesticides, as fungicides and as high-pressure lubricants.
Nickel complexes of phosphine ligands have been studied for
All reagents and solvents were commercially available
high-grade materials (Merck/sd fine/Himedia) and used as
received. The C, H and N contents were determined by
elemental analysis using an Elementar Analysensysteme
Gmbh Vario El V3.00 instrument. IR spectra were recorded
on a Thermo NICOLET AVATAR 330 FT-IR spectro-
-
1
photometer (range: 400–4,000 cm ) as KBr pellets.
A Shimadzu UV-1650 PC double-beam UV–Visible
spectrophotometer was used for recording the electronic
spectra. The spectra were recorded in DMF, and the pure
solvent was used as the reference. Cyclic voltammograms
were recorded on a CHI604C Electrochemical Analyser.
The working electrode was platinum. The counter electrode
was a platinum wire, and reference electrode was Ag/AgCl.
N. Srinivasan ꢀ P. Valarmathi ꢀ S. Thirumaran (&)
Department of Chemistry, Annamalai University,
Annamalainagar, Chidambaram 608 002, India
e-mail: sthirumaran@yahoo.com
S. Ciattini
Centro di Cristallografia Strutturale, Polo Scientifio di Sesto
Fiorentino, Via della Lastruccia No. 3, 50019 Sesto Fiorentino,
Firenze, Italy
123

8
16
Transition Met Chem (2010) 35:815–819
Pure dichloromethane was used as the solvent and tetra-
butylammonium perchlorate (0.10 M) as the supporting
-
1
electrolyte. The scan rate was 100 mV s . All the mea-
surements were recorded at room temperature (27 °C) in an
oxygen-free atmosphere, provided by bubbling purified
nitrogen through the solution. The concentration of the
-
3
-1
compounds was 1 9 10 mol L
.
Preparation of [Ni(dbpdtc) ] (1)
2
0
N,N -Dibenzyl-1,4-phenylenediamine was obtained accord-
ing to the procedure described previously [11]. Triethyl-
amine (0.53 mL, 3.82 mmol) and CS2 (0.22 mL, 3.82
0
mmol) were added to a solution of N,N -dibenzyl-1,
-phenylenediamine (0.51 g, 1.74 mmol) in THF (10 mL).
4
The mixture was stirred for 2 h before adding more sol-
vent to 40 mL. Then, a solution of NiCl ꢀ6H O (0.4 g,
2
2
1
.74 mmol) in H O (4 mL) was added dropwise, and the
2
mixture was stirred for 15 h at room temperature. The solid
product was filtered off, washed with CH Cl (30 mL) and
2
2
dried under vacuum (Scheme 1). Suitable single crystals
for X-ray structure analysis were obtained by repeated
crystallization from methanol. Found (%): C, 63.9; H, 4.8;
N, 6.9. Anal. Calcd (%): C, 64.2; H, 4.9; N, 7.1.
Preparation of [Ni(dbpdtc)(PPh )(NCS)] (2)
3
A mixture of [Ni(dbpdtc) )] (0.55 g, 1.0 mmol), PPh
2
3
(
0.524 g, 2.0 mmol), NiCl ꢀ6H O (0.237 g, 1.0 mmol) and
2
2
Scheme 1 Preparation of Ni(dbpdtc)
2
NH SCN (0.152 g, 2.0 mmol) was refluxed for 3 h in
4
chloroform–methanol solvent mixture (3:2, 50 mL). The
purple-red solution obtained was filtered and left for
evaporation. After 2 days, a purple-red solid separated out,
which was recrystallized from chloroform. The complex
˚
radiation (k = 0.71073 A) at ambient temperature. The
structure was solved by SHELXS [12] and refined by full-
matrix least-squares methods in SHELXL [12]. All the non-
hydrogen atoms were refined anisotropically, and the
hydrogen atoms were refined isotropically. Details of
the crystal data and structure refinement parameters for 1 are
summarized in Table 1. Selected bond distances and angles
are presented in Table 2. Crystallographic data have been
deposited with the Cambridge Crystallographic Centre as
supplementary publication number CCDC-673376. Copies
of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CBZ, 1EZ, UK.
analysed to [Ni(dbpdtc)(PPh )(NCS)]. Found (%): C, 64.6;
3
H, 4.5; N, 5.7. Anal. Calcd (%): C, 64.7; H, 4.6; N, 5.7.
Preparation of [Ni(dbpdtc)(PPh ) ]ClO (3)
3
2
4
A mixture of [Ni(dpbdtc) ] (0.55 g, 1.0 mmol), NiCl ꢀ6H O
2
2
2
(
(
0.237 g, 1.0 mmol), PPh (1.048 g, 4.0 mmol) and NaClO
3 4
0.242 g, 1.0 mmol) was refluxed for 3 h in chloroform–
methanol solvent mixture (3:2, 50 mL). The purple-red
solution obtained was filtered and left for evaporation. After
2
days, a purple-red solid separated out, which was recrys-
tallized from chloroform. The complex analysed to
Results and discussion
[
Ni(dbpdtc)(PPh ) ]ClO . Found (%): C, 63.3; H, 4.5; N,
3 2 4
2
.5. Anal. Calcd (%): C, 63.5; H, 4.6; N, 2.6.
Spectroscopic and voltammetric studies
X–Ray crystallography
The important IR bands of the complexes are listed in
Table 3. The energy of the mC-N band for the dithiocar-
bamates was intermediate between the stretching frequen-
cies associated with typical single- and double-bonded
Diffraction data for 1 were recorded on an Xcalibur-3/CCD
diffractometer using graphite monochromated MoKa
1
23

Transition Met Chem (2010) 35:815–819
817
Table 1 Crystal data, data collection and refinement parameters for
[
ligand towards the metal atom, which increases the con-
tribution of the polar thioureide form in 2 and 3. This
observation indicates increased strength of the thioureide
bond due to the presence of p-accepting phosphines [14].
The mC-S stretching vibrations are observed around
2
Ni(dbpdtc) ]
Empirical formula
FW
42 38 4 4
C H N S Ni
785.72
Crystal system
Space group
Monoclinic
P21/c
-
1
1,025 cm without any splitting, supporting the bidentate
coordination of the dithiocarbamate ligand. The observed
Unit cell dimension
-
1
stretching frequency at 2,100 cm for 2 is attributed to the
˚
a (A)
7.9565(3)
17.4120(7)
13.9776(7)
90.00
N-coordinated thiocyanate. The intense signal observed at
-
˚
b (A)
-
1
1
,091 cm for 3 is assigned to ClO . The mN-H bands
˚
c (A)
4
-
appear at ca. 3,360 cm for dbpdtc.
1
a (°)
b (°)
c (°)
In all three complexes, bands below 380 nm are due
to intraligand p–p* transitions, mainly associated with
N–C=S and S–C=S groups, while a band around 380 nm is
due to the n–p* transition [15]. Several authors ascribe the
intense bands around 400 nm to either metal ? ligand or
ligand ? metal charge transfer [16]. In addition to these
charge transfer bands, the electronic spectrum of
99.114(4)
90.00
3
˚
U/A
1911.99(4)
2
Z
-
3
De/g cm
1.365
-1
l/cm
0.762
F(000)
˚
820
[Ni(dbpdtc) ] shows weak bands at 457 and 619 nm. In
2
k/A
a
MoK (0.71073)
previously described dialkyldithiocarbamato complexes of
nickel(II), similar bands were reported and ascribed to
transitions from the lower filled d-orbitals to the unoccu-
h Range/°
Index ranges
3.8-28.4
-10 B h B 9, -18 B k B 22,
-18 B l B 18
pied d
2
2
orbitals [17]. The two bands at 619 and 457 nm
2
x ꢁy
Reflections collected
Observed reflections F
Weighting scheme
11046
3972
therefore correspond to d ? d
transitions, respectively.
2
2
and d ? d
2
2
xy
x ꢁy
z
x ꢁy
0
0
[ 4r(F )
2
2
0
Calc. W = 1/(r (F
) ?
0.0426p)2 ? 1.4324p),
Strong bands at 477 and 510 nm for the complexes
[Ni(dbpdtc)(NCS)(PPh )] and [Ni(dbpdtc)(PPh ) ]ClO ,
(
2
2
0 c
where p = (F ? 2F )/3
3
3 2
4
Number of parameters refined
308
respectively, can also be attributed to d-d transitions.
Comparison of the information already available on similar
compounds of this type leads to the conclusion that the
coordination around the metal centres is probably square
planar [9, 16].
Final R, R
w
(all data)
0.0919, 0.1286
1.087
GOOF
The Ni(II)/Ni(I) reduction potential for the parent
[
Ni(dbpdtc) ] complex was observed at -1,262 mV. Both
2
˚
Table 2 Selected bond distances (A) and angles (°) for [Ni(dbpdtc)
2
]
mixed ligand complexes showed lower one electron
reduction potentials (-567 and -721 mV for complexes 2
and 3, respectively, Fig. 1). These lower potentials indicate
Ni1–S1
Ni1–S2
S1–C1
2.1831(10)
2.2061(10)
1.713(4)
1.715(4)
1.316(4)
1.438(4)
1.487(5)
1.423(6)
1.357(5)
79.48(3)
easier reduction of the mixed ligand complexes, arising
–
from the presence of PPh and NCS ligands on the nickel
3
S2–C1
centre [9].
N1–C1
N1–C9
N1–C2
N2–C15
N2–C12
S1–Ni1–S2
Crystallographic analysis of [Ni(dbpdtc)2]
An ORTEP diagram of complex 1 is shown in Fig. 2.
[
Ni(dbpdtc) ] is mononuclear, with two molecules in the
2
unit cell. The nickel atom lies on an inversion centre with a
distorted square planar environment of the NiS chromo-
4
carbon and nitrogen atoms [13]. The IR spectra of com-
1
phore. The observed distortion of the square planar coor-
dination is attributed to the small bite angle of the
dithiocarbamate ligand [S1–Ni–S2 = 79.48(3)°]. The Ni–S
distances are slightly asymmetric and lie in the expected
range for four coordinate dithiocarbamates [5]. In com-
plex 1, the dithiocarbamate ligands are bidentate, giving
-
plexes 2 and 3 show mC-N bands at 1,479 and 1,478 cm
,
respectively. The shift in mC-N to higher frequencies
compared with the parent complex 1, for which the band is
-
1
observed at 1,461 cm , is assigned to mesomeric delo-
calization of electron density from the dithiocarbamate
123

8
18
Transition Met Chem (2010) 35:815–819
-
Table 3 IR (cm ) and UV (nm) spectral data for complexes 1, 2 and 3
1
-
1
)
Compound
IR (cm
UV (nm)
v
N–H
v
C-N
m
C-S
NCS/ClO
4
[
[
[
Ni(dbpdtc)
Ni(dbpdtc)(NCS)(PPh
Ni(dbpdtc)(PPh ]ClO
2
] (1)
3351
3359
3386
1461
1479
1478
1022
1024
1026
–
619, 457, 410, 336, 252
477, 377, 336, 254
516, 369, 331, 253
3
)] (2)
2100
1091
3
)
2
4
(3)
Fig. 2 ORTEP diagram of [Ni(dbpdtc)
i) 1–x, 1–y, 1–z; (ii) x, 1 ? y, z
2
], symmetry operations
(
only one NH group was deprotonated by the addition of
carbon disulphide in the presence of triethylamine. The
Fig. 1 Cyclic voltammograms of a [Ni(dbpdtc)
(
2 3
]; b [Ni(dbpdtc)(PPh )
NCS)]; c [Ni(dbpdtc)(PPh ]ClO
3
)
2
4
structure of [Ni(dbpdtc) ] shows that the N2–C12 bond
2
˚
distance [1.357(5) A] is shorter than the C–N distance
˚
[1.4182(14) A] in p-phenylenediamine [22], suggesting
four-membered chelate rings [NiS C]. Their planar geom-
2
etry is supported by the corresponding torsion angles which
movement of electron density from N(2) to the phenyl ring.
Due to the reduced electron density on N(2), the N(2)H
group was not deprotonated by the addition of carbon
disulphide. In the case of other diamines, both NH groups
were deprotonated by carbon disulphide owing to the
absence of a comparable resonance effect.
are close to 0 or 180°. The short thioureide C–N distance
˚
C1–N1 = 1.316(4) A] indicates that there is a contribu-
[
tion of the double-bond character to a formally single N–C
2
bond in the dithiocarbamate group i.e., admixture sp -
3
hybridized state to sp orbitals of the nitrogen atom; this
?
would lead to a d surplus charge on the nitrogen atom
-
with corresponding d charge delocalized through the four-
membered CS M ring [18] (Scheme 1). The C–S distances
2
˚
mean 1.714(5) A] are significantly shorter than the typical
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