Synthesis, X-ray structure, spectroscopic properties and DFT studies of some dithiocarbazate complexes of nickel(II)

Article abstract of DOI:10.1016/j.molstruc.2012.07.018

Two nickel(II) complexes with formulae NiL₂ (1) and NiL'Im (2) (HL = allyl 2-benzylidene-hydrazinecarbodithioate, H₂L′ = allyl 2-(2-hydroxybenzylidene)hydrazinecarbodithioate, Im = Imidazole) have been synthesized and characterized by elemental analysis, molar conductivities, FT-IR, ¹H NMR and UV/Vis spectroscopy. The crystal structure of the complexes has been determined by single crystal X-ray diffractometry. Both L and L′ ligands are coordinated to the metal in the thiolate form. In 1, the square planar coordination of the metal is achieved by coordination of two bidentate ligand units acting through azomethine nitrogen and the thiolato sulfur donor atoms. The complex 2 has a square-planar geometry with the tridentate ligand coordinated to the metal through salicylate oxygen, azomethine nitrogen and the thiolato sulfur atoms, while the fourth coordination position is occupied by one N atom of imidazole. Also natural bond orbitals (NBOs), frontier molecular orbitals (FMOs) and Mulliken charge computational studies on complexes carried out in the ground state with the DFT and theory at B3LYP/6-31G(d,p) level of theory.

Full text of DOI:10.1016/j.molstruc.2012.07.018

Journal of Molecular Structure 1031 (2013) 180–185
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, X-ray structure, spectroscopic properties and DFT studies of some
dithiocarbazate complexes of nickel(II)
b,
Reza Takjoo a, , Roberto Centore
⇑
⇑
a Department of Chemistry, School of Sciences, Ferdowsi University of Mashhad, Mashhad 91775-1436, Iran
b Department of Chemical Sciences, University of Naples ‘‘Federico II’’, Via Cinthia, I-80126 Naples, Italy
h i g h l i g h t s
"
"
"
"
"
Two nickel(II) dithiocarbazate complexes are synthesized.
The nickel(II) complexes were prepared and characterized by spectral techniques.
The structures of compounds are determined by X-ray studies.
The complexes show distorted square planar geometries.
The DFT calculations for the optimization, Mulliken charge, FMO and NBO are done.
a r t i c l e i n f o
a b s t r a c t
Article history:
Two nickel(II) complexes with formulae NiL2 (1) and NiL’Im (2) (HL = allyl 2-benzylidene-hydrazinecar-
bodithioate, H2L0 = allyl 2-(2-hydroxybenzylidene)hydrazinecarbodithioate, Im = Imidazole) have been
synthesized and characterized by elemental analysis, molar conductivities, FT-IR, 1H NMR and UV/Vis
spectroscopy. The crystal structure of the complexes has been determined by single crystal X-ray diffrac-
tometry. Both L and L0 ligands are coordinated to the metal in the thiolate form. In 1, the square planar
coordination of the metal is achieved by coordination of two bidentate ligand units acting through azo-
methine nitrogen and the thiolato sulfur donor atoms. The complex 2 has a square-planar geometry with
the tridentate ligand coordinated to the metal through salicylate oxygen, azomethine nitrogen and the
thiolato sulfur atoms, while the fourth coordination position is occupied by one N atom of imidazole. Also
natural bond orbitals (NBOs), frontier molecular orbitals (FMOs) and Mulliken charge computational
studies on complexes carried out in the ground state with the DFT and theory at B3LYP/6-31G(d,p) level
of theory.
Received 19 April 2012
Received in revised form 9 July 2012
Accepted 10 July 2012
Available online 20 July 2012
Keywords:
Dithiocarbazate
NSO donor
NS donor
Cu(II) and Ni(II) complexes
Crystal structures
DFT
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
In dithiocarbazate compounds, owing to thione–thiol tauto-
mery, N and S donor atoms are connected to the metal ion with
During the past years, the synthesis of new coordination com-
pounds containing nitrogen and sulfur donor atoms has been sig-
nificantly developed. Among these materials, dithiocarbazate
compounds have been specifically considered by researchers be-
cause of biological properties such as antibacterial [1], antimalarial
[2], antiviral [3], antitumor [4,5], insecticidal [6] and optoelectronic
properties such as good non-linear optical (NLO) response [7].
Actually, dithiocarbazates constitute one of the most important
classes of mixed hard–soft nitrogen–sulfur donor ligands [8,9]. A
change in the substitution pattern of these compounds can create
new ligands with different properties.
the formation of five- or six-member rings. The presence of addi-
tional donor atoms in suitable position in the compound can in-
crease the coordination ability of the ligand giving rise to
different coordination geometries [10].
The transition metal complexes of dithiocarbazates have differ-
ent geometric, electronic, optical [11], magnetic [12], semiconduct-
ing [13] and radiopharmaceutical properties as well [14].
In particular, planar nickel(II) complexes are coordinatively
unsaturated and can act as Lewis acids [15]; the anticancer [16]
and antimicrobial [17] activity of many nickel complexes, as well
as their NLO performances [18], may be related with that feature.
In order to study allyl group effects on the physico-chemical
properties of dithiocarbazates, we report here the synthesis, char-
acterization and X-ray crystal structures of two new complexes
bis(allyl-2-(phenylmethylene)hydrazinecarbothioamido)nickel(II)
⇑
Corresponding authors. Tel./fax: +98 511 8975457.
E-mail addresses: rezatakjoo@yahoo.com (R. Takjoo), roberto.centore@unina.it
(R. Centore).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.07.018

R. Takjoo, R. Centore / Journal of Molecular Structure 1031 (2013) 180–185
181
2.4. Synthesis of [allyl-2-(2-hydroxyphenyl)methylene]
hydrazinecarbothioamido)imidazole-nickel(II) (2)
S
HL
X = H
CH
X
N
NH
C
S
CH2 CH CH2
X = OH
H2L'
A solution of nickel(II) acetate tetrahydrate (0.4 g, 0.4 mmol) in
ethanol (5 mL) was mixed with a solution of the H2L0 ligand precur-
sor (0.1 g, 0.4 mmol) in the same solvent (5 mL) and the green solu-
tion was heated on a water bath for ca. 5 min whereupon a solution
of imidazole (0.04 g; 0.6 mmol) in ethanol (5 mL) was added. The
brown solution was heated on a water bath for 30 min and then
left to stand overnight. The red crystalline product which formed
after a week was filtered off, washed with ether and dried in a vac-
uum desiccator over anhydrous silica gel.
Scheme 1. Chemical diagrams of the ligand precursors.
(NiL2) and [allyl-2-(2-hydroxyphenyl)methylene]hydrazinecar-
bothioamido)-imidazole-nickel(II) (NiL0Im) where HL, H2L0 and Im
are, respectively, allyl 2-benzylidenehydrazinecarbodithioate (HL),
allyl 2-(2-hydroxybenzylidene)hydrazinecarbodithioate (H2L0) and
imidazole, see Scheme 1.
Moreover, we also present the DFT calculations to investigate
the geometry, electronic structure atomic charge distributions
and bond analysis of the complexes.
Yield: 0.04 g, 27%. m.p.: 187 °C. Molar conductance (10ꢀ3 M,
DMF) 0.65 ohmꢀ1 cm2 molꢀ1
. Anal. Calc. for C14H14N4NiOS2
(317.11 g molꢀ1): C, 44.59; H, 3.74; N, 14.86; S, 17.01; Ni, 15.56.
Found: C, 43.85; H, 3.80; N, 14.76; S, 16.60; Ni, 14.89%. IR (KBr)
cmꢀ1
1030s,
:
m
m
(NH) 3053w,
m(C@N) 1595s, m(CAO) 1525 m, m(NAN)
(CAS) 960 m. 1H NMR (100 MHz, CDCl3, 25 °C, ppm):
d = 3.78 (d, 2H; C9), 5.26 (dd, 2H; C11), 5.8–6.2 (m, 1H; C10),
6.7–7.2 (m, 4H; phenol ring), 7.2–7.4 (m, 2H; C14, C13), 7.85 (s,
1H; C12), 8.14 (s, 1H; C7), 10.4 (bs, 1H; NH imidazole). UV/Vis
(CHCl3) kmax
383(4.03), 419(2.78).
2. Experimental
, nm (loge,
L molꢀ1 cmꢀ1): 243(4.38), 270(4.23),
2.1. Reagents
All the material were purchased form Merck Chemical Company
and were used as received. All solvents were reagent grade and
used without further purification. Allyl 2-benzylidene-hydrazine-
carbodithioate (HL) and allyl 2-(2-hydroxybenzylidene) hydrazine-
carbodithioate (H2L0) were prepared by previously reported
procedures [8,19].
2.5. X-ray structure determination
Single crystals of 1 and 2 suitable for X-ray analysis were grown
from DMF. Data were collected on a Bruker-Nonius Kappa-CCD dif-
fractometer using graphite monochromated MoK
a radiation
(k = 0.71073 Å) at 173 K. Absorption correction was performed
using the multi-scan method [20]. The structures were solved by
direct methods [21] and refined by the full matrix least squares
method [22] on F2 against all reflections, using anisotropic dis-
placement parameters for non-H atoms. The positions of H atoms
were determined stereochemically, with exception for the NAH
atoms of imidazole rings of 2, whose positions were determined
in difference Fourier maps. Refinement of H atoms was performed
by the riding model with Uiso = 1.2Ueq of the carrier atom. In the
case of 1 the investigated crystal specimens resulted twinned by
rotation of 180° around the b axis. Many attempts to select a
non-twinned specimen failed, so the X-ray analysis was eventually
performed on a twinned sample. During the refinement, the twin-
ning was handled with the TWIN instruction of the Shelxl package
[22] using the proper rotation matrix (ꢀ100/010/00ꢀ1) and
assuming racemic twinning. That accounts for the higher final R
2.2. Physical measurements
C, H, N, S elemental analyses were performed using a Thermo
Finnigan Flash 1112EA elemental analyzer. The IR spectra in the
range 4000–400 cmꢀ1 were recorded from KBr pellets using a Buck
500 Scientific spectrometer. The mass spectra were recorded on a
MAT CH7A. Proton NMR spectra were recorded on a Bruker BRX
100 AVANCE spectrometer with TMS as internal standard. The
electronic spectra were recorded in DMF with a SHIMADZU model
2550 UV–Vis spectrophotometer (260–900 nm). The molar con-
ductance values of 10ꢀ3 M DMF solutions of the complexes were
measured with a Metrohm 712 Conductometer.
2.3. Synthesis of bis(allyl-2-
(phenylmethylene)hydrazinecarbothioamido)nickel(II) (1)
Table 1
Crystal, collection and refinement data for 1 and 2.
Nickel(II) chloride hexahydrate (0.2 g, 1 mmol) in boiling etha-
nol (10 mL) was added to the ethanol solution (10 mL) of the HL li-
gand precursor (0.48 g, 2 mmol). The mixture was heated in a
water bath for 30 min and then left to stand overnight. The brown
product was filtered off, washed with ethanol and dried in a vac-
uum desiccator over anhydrous silica gel. The complex was recrys-
tallized from DMF/ethanol to obtain diffraction quality crystals.
Yield: 0.30 g, 56%. m.p.: 140 °C. Molar conductance (10ꢀ3 M,
Compound
1
2
Chem. formula
Formula weight
T (K)
Crystal system
Space group
a (Å)
(C11H11N2S2)2Ni (C14H14N4OS2)Ni
529.39
173(2)
Monoclinic
P21/n
377.12
173(2)
Triclinic
P ꢀ 1
4.243(3)
8.386(1)
b (Å)
c (Å)
19.284(8)
14.070(6)
90/96.15(2)/90
1145(1), 2
1.536
9.7680(7)
19.052(3)
86.221(8)/83.88(1)/76.071(8)
1504.8(3), 4
1.665
DMF) 2.5 ohmꢀ1 cm2 molꢀ1
.
Anal. Calc. for C22H22N4NiS4
a
/b/c (°)
V(Å3), Z
(529.39 g molꢀ1): C, 52.35; H, 4.97; N, 11.10; S, 25.41; Ni, 11.09.
Found: C, 52.58; H, 4.78; N, 11.07; S, 24.94; Ni, 10.68%. IR (KBr)
Density (g/cm3)
Absorption coefficient
h max
1.231 mmꢀ1
24.99°
1.572 mmꢀ1
27.5°
cmꢀ1
(C@N + C@S) 1178 m,
:
m
(C@C) 1640w,
m
(C@N) 1595 m,
m
(C@Cring
)
1487w,
m
m
(NAN) 1025s,
m
(CAS) 950 m. 1H NMR
Indep. refl.
4523
6655
Data/param.
R, wR (I > 2(I))
R, wR (all data)
4523/142
0.0987, 0.2482
0.1313, 0.2586
6655/397
0.0662, 0.1472
0.1068, 0.1566
0.708, ꢀ0.549
(100 MHz, CDCl3, 25 °C, ppm): d = 3.8 (d, 2H; C9), 5.1–5.4 (dd,
2H; C11), 5.7–6.2 (m, 1H: C10), 7.4–7.8 (m, 5H; ring), 8.1 (s, 1H;
C7). UV/Vis (CHCl3) kmax, nm (loge
, L molꢀ1 cmꢀ1): 256(4.40),
Max. peak and hole (e/Å3) 1.815, ꢀ0.743
285(4.47), 317(4.45), 450(4.95).

182
R. Takjoo, R. Centore / Journal of Molecular Structure 1031 (2013) 180–185
factors and residual electronic density. A summary of crystal, col-
lection and refinement data is shown in Table 1.
Compound 2: IR spectral assignment of the complex 2 does not
show any medium bands in the regions 3200 and 3097 cmꢀ1 due to
the v(OAH) and v(NAH) vibrations, respectively, providing strong
evidence for ligand coordination around the nickel(II) ion in its
deprotonated form. The v(C@N) band at 1595 cmꢀ1 show a red
shift at about 15 cmꢀ1 related to ligand. The coordination of the li-
gand in the thiolate form is confirmed by the absence of v(C@S)
and v(CSS) bands. These peaks are observed at 1319 and
1095 cmꢀ1 in the free ligand. No significant change is observed
for v(NAN) after coordination. The coordination of phenoxy oxygen
to the metal is supported by the increase in v(CAO). Presence of
imidazole moiety is confirmed with a peak at 3053 cmꢀ1 related
to NAH vibration of imidazole.
2.6. Theoretical calculations
The gas phase geometry of all compounds was fully optimized
using density functional theory (DFT) at the B3LYP/6-31G(d,p) ba-
sis set [23,24] levels (the standard 6-31G(d,p) basis sets for N, C, H,
S, O elements) and employing the Windows versions of Gaussian
98 (G98W) [25]. Geometries of complexes 1 and 2 were fully opti-
mized. Multiplicity of the Ni(II) central atom was considered as 1
for all complexes. No symmetry constraints were applied in the
calculations. At the same level and basis sets, calculations of natu-
ral electron population, natural charge for each atom and frontier
molecular orbitals of the compounds have been performed by nat-
ural bond orbital (NBO) analysis [26] on the gas phase optimized
structures.
The 1H NMR spectrum in CDCl3 of compound 2 does not display
bands corresponding to NH and SH that confirm the presence of
thiolate form of the ligand in the complex.
The electronic spectral data for the H2L0 and complex 2 are re-
corded in the range of 200–900 nm (CHCl3). The two bands at
243 and 270 nm are attributed to
p ?
pꢁ of ring and dithiocarbaz-
ate moiety respectively. The n ? pꢁ transition was observed at 383,
351 and 360 nm in the free ligand, but after complexation just a
broad band was detected at 383 nm. The intense band at 419 nm
is LMCT band. The tail of this band covers all d–d transition.
3. Results and discussion
The HL and H2L0 Schiff bases of S-allyldithiocarbazate have the
thioamide function AN(H)C(S) in which the thione form had to
be converted to the thiolate form so that the complexation can oc-
cur [27]. Although the thione form of the ligands is stable in solid
state, it converts to thiolate form in solution and in the presence of
metal ions and mild bases [28]. After deprotonation, the ligand L is
bidentate (N,S) with charge ꢀ1, while L0 is tridentate (O,N,S) with
charge ꢀ2. So, it is expected that the complex of L with Ni(II), i.e. 1,
is bischelate, while in the case of 2 the complex is formed by one
ligand molecule (monochelate tridentate) plus another neutral
monodentate ligand molecule (imidazole). The molar conductivi-
ties of the complexes in DMF indicate that they are non-electrolyte
compounds. Elemental analysis, spectral studies and X-ray crystal-
lography have finally confirmed the structure of these compounds.
3.2. X-ray structure analysis
Ortep diagrams of 1 and 2 are reported in Figs. 1 and 2 respec-
tively. Selected geometric parameters are given in Table 2. The
X-ray analysis confirms that 1 is a bischelate complex of point
symmetry Ci, as the nickel atoms lie on crystallographic inversion
centres, while 2 is a monochelate complex with an additional neu-
tral ligand (imidazole) coordinated to the metal. The square planar
coordination geometry is fairly regular in both the complexes, with
the four bond angles around the metal all close to 90°. In particular,
3.1. Spectroscopic characterization of complexes
Compound 1: the m(NAH), m(CSS) and m(C@S) bonds in free li-
gand at 3105 cmꢀ1, 1334 cmꢀ1 and 1097 disappear in complexes
spectra that indicating deprotonation of ligand during the com-
plexation [29]. Lowering m
(C@N) from 1609 cmꢀ1 in the ligand to
1598 cmꢀ1 in the nickel complex reveals that azomethine nitrogen
is coordinated to metal [29]. The bands at 1640 and 1025 cmꢀ1
were assigned for m(NAN) and m(C@C) stretching energy increase.
The 1H NMR spectrum of NiL2 in CDCl3 does not show any peaks
at ca. d 13.33 ppm and 4 ppm attributed to the resonances of N2H
and S1H protons, that indicating that the ligand is coordinated in
the thiolate form. The upfield shift of the azomethine proton from
7.9 ppm to 8.1 ppm suggests that the coordination occurs via azo-
methine nitrogen atom of ligand.
Fig. 1. Ortep diagram of 1. Thermal ellipsoids are drawn at 50% probability level.
The electronic spectrum of the NiL2 complex shows two bands
in the 285 and 256 nm regions which can be assigned to the
p
?
pꢁ transition of the azomethine group and ring, respectively.
These bands are observed at 295 and 240 nm in the spectrum of
the free ligand. The band at 317 nm can be assigned to the
n ? pꢁ transition of the dithiocarbazate moiety. Bands attributed
to this transition appeared at 334 and 345 nm in HL spectrum. In
addition, S ? Ni(II) charge transfer band appeared at approxi-
mately 450 nm. In the electronic spectrum of a square-planar nick-
el complex, it is expected that three bands corresponding to the
transition 1A1g ? 1A2g 1A1g ? 1B1g and 1A1g ? 1Eg are seen, but
,
the presence of sulfur covers these bands under its very intense in-
ter-ligand and charge transfer band; hence, the mentioned bands
are not observed.
Fig. 2. Ortep diagram of one independent molecule of 2. Thermal ellipsoids are
drawn at 50% probability level.

R. Takjoo, R. Centore / Journal of Molecular Structure 1031 (2013) 180–185
183
Table 2
by torsion around the NiAN3 bond (Fig. 3). Moreover, the two
independent molecules are oriented with their coordination planes
very little tilted with respect to each other (the dihedral angle be-
tween the mean planes is 8.2(2)°) (Fig. 3).
Selected bond lengths (Å) for 1 and 2, with esd’s in parentheses.
Compound
1
2
Experimental
Calculated
Experimental
Calculated
The conformation of the ligands is different in the two com-
plexes. In fact, the bond C7@N1 is trans in 2 while it is cis in 1; this
is probably a consequence of the higher steric overcrowding in the
bischelate complex 1. Also the conformation of the allyl group is
different in the two compounds. In fact, C9 is trans with respect
to S1 in 1 while it is cis in 2. So, the overall shape of the ligand is
bent in 1, while it is extended in 2.
At variance of 1, whose packing is determined by normal van
der Waals contacts, the packing of 2 is conditioned by the forma-
tion of H bonds. In particular, molecules in 2 are arranged in chains
through H bonding between the NAH donor of the imidazole li-
gand of a molecule and the N2 acceptor of the other independent
molecule. The H bonded chains run parallel to c (Fig. 4). According
to our previous researches, the presence of allyl moiety in these
compounds produces hydrogen interactions, which in turn they
play a role in lattice expanding [30,31]. But this effect is just seen
in the complex 2 in which hydrogen bonds of S1Bꢂ ꢂ ꢂH9AAC9A,
C11Aꢂ ꢂ ꢂH5AAC5A, C10Bꢂ ꢂ ꢂH2AAC14A and C11Bꢂ ꢂ ꢂH13AAC13A
cause the expansion of crystalline structure. There is not any allyl
interaction in the compound 1. This lack of interaction is seen in
some similar cases [32].
NiAS1
C7AN1
N1AN2
C8AN2
C8AS1
C8AS2
NiAN1
NiAN3
NiAO1
2.175(2)
1.300(8)
1.403(7)
1.281(8)
1.722(7)
1.745(6)
1.928(5)
2.254
1.303
1.338
1.301
1.743
1.767
1.948
2.149(2), 2.137(2)
1.313(8), 1.286(8)
1.400(7), 1.416(7)
1.294(8), 1.291(8)
1.719(7), 1.719(6)
1.750(7), 1.752(7)
1.860(5), 1.865(5)
1.923(5), 1.915(5)
1.853(5), 1.837(5)
2.229
1.309
1.387
1.294
1.750
1.779
1.883
1.954
1.864
In the crystals of 2, molecules are arranged with their coordina-
tion planes approximately parallel to each other and lying on the
planes of the family with Miller indices 220 (the reflection 220 is
the second most intense of the whole diffraction pattern) (Fig. 5).
The Bragg spacing d220 = 3.502 Å is also the average stacking dis-
tance of the molecules along a + b.
Fig. 3. The two crystallographically independent molecules of 2.
the bite angles corresponding to the formation of the five-
membered rings are slightly contracted (N1ANiAS1 = 85.7(2)° in
1, 87.0(2), 86.7(2)° in 2) and the others slightly enlarged. The metal
and the four atoms to which it is bonded are strictly planar in 1 and
are planar within 0.069(3) Å and 0.022(3) Å in the A and B inde-
pendent molecules of 2 respectively. In both the complexes, the
metal-to-nitrogen distances are, on average, 0.2 Å shorter than
the metal-to-sulfur distances. The inspection of the bond lengths
clearly indicates that the coordinated ligand is in the thiolato form
in both complexes. This is strongly suggested, in particular, by the
bond lengths C7AN1 (1.300(8) Å in 1, 1.313(8), 1.286(8) Å in 2) and
C8AN2 (1.281(8) Å in 1, 1.294(8), 1.291(8) Å in 2) which take
values close to those expected for a double bond.
The two crystallographically independent molecules of
mainly differ for the orientation of the imidazole ligand with re-
spect to the coordination plane (Fig. 3).
In fact, the dihedral angle between the mean coordination plane
and the average plane of the imidazole ligand is 14.7(3)° in the
molecule A and 33.4(3)° in B; the different orientation is achieved
3.3. Geometry optimization, charge distribution and electronic
structure
In the complexes, the calculated bond lengths and angles are in
a good agreement with the values based upon the X-ray crystal
structure data (see Table 2). A difference between the experimental
and theoretical studies is that computations were done in the gas
phase, whereas the X-ray data was obtained in the solid phase
for complexes.
The calculated charges on the nickel atom in complexes
(1 = 0.16 and 2 = 0.36) are considerably lower than the formal
charge +2, that confirming a significant charge donation from the
ligands. In compound 1, the calculated Mullikan charge for the
atoms S1 and S1i is less than ꢀ1 and the electron density in valence
3s and 3p orbitals is lower than the predicted values.
2
In the complex 2, the calculated Mulliken charge values for S1
and O are ꢀ0.099 and ꢀ0.643 respectively, that is less than the
Fig. 4. A chain of H-bonded molecules in 2. Structural parameters of the H bonds [33]: N4AAHꢂ ꢂ ꢂN2Bi: 1.03 Å, 1.98 Å, 2.971(8) Å, 160.2°, i = ꢀx, ꢀy, ꢀz; N4BiiAHꢂ ꢂ ꢂN2A:
1.02 Å, 1.98 Å, 2.982(8) Å, 166.4°, i = ꢀx, ꢀy, 1 ꢀ z.

184
R. Takjoo, R. Centore / Journal of Molecular Structure 1031 (2013) 180–185
ligand, from the metal and the imidazole ligand, while in the LUMO
the electron density is essentially established on the L0 ligand and,
to a lesser extent, on the metal, without relevant contributions
from imidazole. Since the first electron transfer occurs from the
highest occupied molecular orbital (HOMO) to lowest unoccupied
molecular orbital (LUMO), it can be inferred that the first electron
transfer in 1 is related to LMCT while in complex 2 the first low en-
ergy electronic transition is combined MLCT from metal to organic
moiety and intra ligand g ? gꢁ electron transition. Additional infor-
mation on the NBO calculations is presented in Table 3. According
to this table, the electron populations on s and p orbitals of oxygen,
nitrogen and sulfur donor atoms in both complexes are less than
the expected values of valance orbitals, while the computed elec-
tron population in central ion in both complexes is more than
the expected value in Ni+2 with d8 electron configuration. This con-
firms the electron transmission of donor atoms toward the central
metal.
Fig. 5. Crystal packing of 2 viewed down c.
formal charge. Similarly, the electron density of these atoms is
lower than expected values. All those results indicate electron
transfer from the donor atoms to the central metal.
4. Conclusion
Calculated HOMO and LUMO frontier orbitals of the two com-
plexes are drawn in Fig. 6 and they show relevant differences. In
fact, in 1 the HOMO is mainly localized on the phenyl ring, while
in the LUMO major contributions come from the metal and, to a
lesser extent, from the allyl tail. On the other hand, in 2, the elec-
tron density of the HOMO shows contributions from the whole L0
Two Ni(II) complexes derived from bi- and tri-dentate S-ally-
ldithiocarbazates ligands were prepared. The characterization of
the complexes was performed in solution by UV and H NMR spec-
troscopy and in the solid state by single crystal X-ray analysis.
Those analyses showed that the HL (N,S) and H2L0 (N,S,O) Schiff
Fig. 6. Calculated HOMO and LUMO for 1 (a) and 2 (b).
Table 3
The natural charges of selected atoms of the studied complexes determined by using of B3LYP/6-31G method.
1
2
Atom
Charge
Configuration
Atom
Charge
Configuration
Ni
Ni
S1
S1i
N1
N1i
0.164257
0.164257
ꢀ0.086425
ꢀ0.086425
ꢀ0.303308
ꢀ0.303308
[core]4S(0.40)3d(8.87)
[core]4S(0.40)3d(8.87)
[core]3S(1.71)3p(4.34)
[core]3S(1.71)3p(4.34)
[core]2S(1.30)2p(3.93)
[core]2S(1.30)2p(3.93)
Ni
Ni
S1
O
N1
N3
0.364010
0.364010
ꢀ0.098864
ꢀ0.642692
ꢀ0.329113
ꢀ0.428446
[core]4S(0.36)3d(8.78)
[core]4S(0.36)3d(8.78)
[core]3S(1.71)3p(4.38)
[core]2S(1.65)2p(4.99)
[core]2S(1.30)2p(3.97)
[core]2S(1.33)2p(4.15)

R. Takjoo, R. Centore / Journal of Molecular Structure 1031 (2013) 180–185
185
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with square-planar coordination geometry.
The small calculated values of the Mulliken charge on nickel
atoms in the two complexes confirm donor ability of ligands to
nickel(II) centre. Furthermore, HOMO and LUMO studies showed
that in NiL2 and NiL0Im the low energy electronic transition is re-
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Appendix A. Supplementary material
CCDC 867832 and 867833 contain the supplementary crystallo-
graphic data for complexes NiL2 and NiL0Im respectively. These
data can be obtained free of charge via http://www.ccdc.cam.a-
c.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. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.molstruc.2012.07.018.
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