Syntheses and characterization of some homoleptic (1,1-dithiolato) copper(II) and nickel(II) complexes, and mixed-ligand (1,1-dithiolato)nickel(II) chelates containing nitrogenous bases. Crystal structures of tetrabutylammonium

Article abstract of DOI:10.1016/j.poly.2005.06.043

A series of divalent nickel and copper complexes and a series of mixed-ligand nickel(II) chelates have been prepared and characterized. The general formula of the complexes is [cation]₂[M(1,1-dithiolate) ₂] (M = Ni(II), Cu(II)), and that of the mixed-ligand is [Ni(enR)(SS)], containing the dianion of 1,1-dithiolate derivatives and an N-alkyl- or N-phenyl-substituted 1,2-diaminoethane or a bidentate nitrogenous base, enR. The structures of the complexes, both in the solid state and in solution, have been determined by IR, UV-Vis, room temperature magnetic and electrical conductance measurements. The MS₄ chromophoric group is common to all of the homoleptic complexes and contains two four-membered chelate rings. The MS₂N₂ chromophoric group is common to the mixed-ligand complexes. The 1,1-dithiolate derivatives are substituted isomaleonitriles of the formula Y(CN)CCS22-, where Y = CONH₂ (1-cyano-1-carboamido-2,2-ethylenedithiolate, CCED); COOEt (1-cyano-1- carboethoxy-2,2-ethylenedithiolate, CED); ph (1-cyano-1-phenyl-2,2- ethylenedithiolato, CPD) and Cl-ph (1-cyano-1-chlorophenyl-2,2- ethylenedithiolate, CCPD). X-ray structural analyses were performed for three compounds. The tetrabutylammonium(1-cyano-1-chlorophenyl-2,2-ethylenedithiolato) copper(II) complex consists of three molecules per unit cell. The copper atom lies on a crystallographic center of symmetry which requires the CuS₄ unit to be planar. The average Cu-S bond length is 2.204 ?. In the unit cell of the complex [(2,2′-bipyridine)(1-cyano-1-phenyl-2,2- ethylenedithiolato)nickel(II)] there are six nickel atoms. In the immediate vicinity of each nickel atom exist two sulfur and, at a shorter distance, two nitrogen atoms. The molecules in the unit cell are arranged in pairs, each pair forming two weak intermolecular Ni?S bond interactions at a distance of 3.617 ?. In the novel sulfur-rich ligand 5-amino-4-(4-chlorophenyl)-[1,2] dithiole-3-thione, three carbon atoms are linked with two sulfur atoms forming a five-membered ring. All observed intramolecular bond lengths in the sulfur ring indicate delocalization of the π-electron system.

Full text of DOI:10.1016/j.poly.2005.06.043

Polyhedron 24 (2005) 2944–2954
www.elsevier.com/locate/poly
Syntheses and characterization of some homoleptic
(1,1-dithiolato)copper(II) and nickel(II) complexes, and mixed-ligand
(1,1-dithiolato)nickel(II) chelates containing nitrogenous bases.
Crystal structures of tetrabutylammonium(1-cyano-1-chlorophenyl-
2,2-ethylenedithiolato)copper(II), [(2,20-bipyridine)(1-cyano-1-
phenyl-2,2-ethylenedithiolato)nickel(II)], and 5-amino-4-
(4-chlorophenyl)-[1,2] dithiole-3-thione
a,
a
b
Hussein H. Alkam *, Khalid M. Kanan , Christos C. Hadjikostas
a
Department of Chemistry and Chemical Technology, Faculty of Science and Technology, Al-Quds University,
Abu-Dies, 20002 Jerusalem, West Bank, Israel
b
Department of Chemistry, University of Thessaloniki, 54006 Thessaloniki, Greece
Received 10 April 2005; accepted 6 June 2005
Available online 10 August 2005
Abstract
A series of divalent nickel and copper complexes and a series of mixed-ligand nickel(II) chelates have been prepared and char-
acterized. The general formula of the complexes is [cation]2[M(1,1-dithiolate)2] (M = Ni(II), Cu(II)), and that of the mixed-ligand is
[Ni(enR)(SS)], containing the dianion of 1,1-dithiolate derivatives and an N-alkyl- or N-phenyl-substituted 1,2-diaminoethane or a
bidentate nitrogenous base, enR. The structures of the complexes, both in the solid state and in solution, have been determined by
IR, UV-Vis, room temperature magnetic and electrical conductance measurements. The MS4 chromophoric group is common to all
of the homoleptic complexes and contains two four-membered chelate rings. The MS2N2 chromophoric group is common to the
2ꢀ
mixed-ligand complexes. The 1,1-dithiolate derivatives are substituted isomaleonitriles of the formula YðCNÞC@CS2
,
where Y = CONH2 (1-cyano-1-carboamido-2,2-ethylenedithiolate, CCED); COOEt (1-cyano-1-carboethoxy-2,2-ethylenedithio-
late, CED); ph (1-cyano-1-phenyl-2,2-ethylenedithiolato, CPD) and Cl-ph (1-cyano-1-chlorophenyl-2,2-ethylenedithiolate, CCPD).
X-ray structural analyses were performed for three compounds. The tetrabutylammonium(1-cyano-1-chlorophenyl-2,2-ethylenedi-
thiolato)copper(II) complex consists of three molecules per unit cell. The copper atom lies on a crystallographic center of
symmetry which requires the CuS4 unit to be planar. The average Cu–S bond length is 2.204 A. In the unit cell of the complex
[(2,20-bipyridine)(1-cyano-1-phenyl-2,2-ethylenedithiolato)nickel(II)] there are six nickel atoms. In the immediate vicinity of each
˚
nickel atom exist two sulfur and, at a shorter distance, two nitrogen atoms. The molecules in the unit cell are arranged in pairs,
˚
each pair forming two weak intermolecular Niꢁ ꢁ ꢁS bond interactions at a distance of 3.617 A. In the novel sulfur-rich ligand
5-amino-4-(4-chlorophenyl)-[1,2]dithiole-3-thione, three carbon atoms are linked with two sulfur atoms forming a five-membered
ring. All observed intramolecular bond lengths in the sulfur ring indicate delocalization of the p-electron system.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Keywords: 1,2-Diaminoethane; Nitrogenous base; Copper(II) complexes; Nickel(II) complexes; Dithiole; Thione; 1,1-Dithiolato
*
Corresponding author. Tel.: +9722 2799502, 2799753; fax: +9722 2796960.
E-mail address: halkam61@yahoo.com (H.H. Alkam).
0277-5387/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.06.043

H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
2945
1. Introduction
2. Experimental
Complexes containing 1,1-dithiolato ligands have
been used as fungicides, pesticides, vulcanization accel-
erators, flotation agents, lubricant additives and in
deposition of ZnS or CdS thin films by metal organic
chemical vapor deposition [1]. 1,1-Dithiolate ligands
have recently attracted much attention mainly because
of the interesting photophysical properties derived
from their extensive electron delocalization onto all
of the ligand atoms [2]. Indeed, the increasing renewed
attention paid nowadays to these species arises from
their high stability, solvatochromic behavior, room-
temperature luminescence in solution [3] and their sta-
tus as excellent candidates for applications such as
photocatalysis [4]. A lot of work is currently taking
place to find how the excited-state properties can be al-
tered in a predictable manner through systematic li-
gand modification [4a]. In addition the variable
coordination modes of 1,1-dithiolate ligands to metals
make the structural studies more interesting [5]. The
1,1-dithiolate ligands have also been used to stabilize
unusually high oxidation states [6] or to facilitate the
syntheses of clusters [5,7], and to the syntheses of
inorganic–organic hybrid materials, which have a
potential in various applications such as electrical con-
ductivity, magnetism [8], ion exchange, separation and
catalysis [9].
2.1. Reagents
The nitrogenous bases, enR, N,N0-diphenyl-1,2-
diaminoethane (PhenPh), N,N0-dibenzyl-1,2-diaminoe-
thane (BenB), cis-1,2-diaminocyclohexane (C · NN),
2-(aminomethyl)pyridine (ampy), 2,20-bipyridine (bipy)
and 2,20-dipyridylamine (dipyamH) were purchased
from Aldrich. The nitriles, malononitrile (NCCH2CN),
ethyl cyanoacetate (NCCH2COOC2H5), cyanoaceta-
mide (NCCH2CONH2) chlorobenzyl cyanide (NCCH2-
C6H4Cl), benzyl cyanide (NCCH2C6H5), tetrabutylam-
monium bromide (n-Bu4NBr) and tetraethylammonium
bromide (Et4NBr) were procured from Merck. Cop-
per(II) chloride dehydrate, CuCl2 Æ 2H2O, nickel(II)
chloride hexahydrate, NiCl2 Æ 6H2O and sodium hydride
(NaH, as 55% suspension) were procured from Fluka.
The dithiolate ligand salts disodium 1-cyano-1-chlor-
ophenyl-2,2-ethylenedithiloate dehydrate (Na2CCPD Æ
2H2O), disodium 1-cyano-1-phenyl-2,2-ethylenedithio-
late dihydrate (Na2CPD Æ 2H2O), disodium 1,1-dicyano-
2,2-ethylenedithiolate trihydrate (Na(i-MNT) Æ 3H2O),
dipotassium 1-cyano-1-carboethoxy-2,2-ethylenedithio-
late hydrate (K2CED Æ H2O) and dipotassium 1-cyano-
1-carbamyl-2,2-ethylenedithiolate dehydrate (K2CCED Æ
2H2O) were prepared by the literature procedures
[11,12].
Previously we reported the synthesis and spectro-
scopic investigation of some mixed-ligand nickel(II)
and copper(II) chelates containing diamine or phos-
phine and 1,1-dithiolate ligands [10]. The results of
these studies indicated that their spectroscopic proper-
ties and magnetic behavior strongly depend upon struc-
tural details of both the diamine or phosphine and the
dithiolate ligands. In this work we describe the synthe-
sis and structural characterization of: (a) nickel(II) and
copper(II) complexes containing 1,1-disubstituted-2,2-
ethylene-dithiolates; (b) a series of neutral ternary
nickel(II) chelates with N-donor, N-acceptor, cross-
conjugated nitrogenous bases and 1,1-dithiolate; and
(c) the fascinating sulfur-rich dithiole ligand. Further
the structures of (2,20-bipyridine)(1-cyano-1-phenyl-2,2-
ethylenedithiolato) nickel(II) [Ni(bipy)CPD], tetrabuty-
lammonium(1-cyano-1-chlorophenyl-2,2-ethylenediti-
olate)copper(II) ((n-Bu4N)2[Cu(CCPD)2]) and the novel
5-amino-4(4-chlorophenyl)-[1,2] dithiole-3-thione li-
gand (ACDT) were elucidated by X-ray diffraction
studies. To the best of our knowledge, this is the first
X-ray study of a nickel(II) complex with a 1,1-dithio-
late having molecular interactions in the solid state,
and the first 1-cyano-1-chlorophenyl-2,2-ethylenedi-
thiolato complex of any metal, and the second X-ray
analysis for copper(II) complexes [21a] with 1,1-dithio-
late ligands.
2.1.1. Synthesis of homoleptic nickel(II) and copper(II)
chelates
The new chelates [R4N]2[M(S2C@C(CN)Y)2]
(Y = Cl-ph, ph, COOEt, CONH2) were prepared
according to the following general method.
To a methanolic solution (ca. 100 cm3) containing
4 mmol of the appropriate 1,1-dithiolate salt, 4 mmol
of tetrabutylammonium bromide (n-Bu4NBr) or tetra-
ethylammonium bromide (Et4NBr) were added. Upon
dissolution, the mixture was filtered slowly into a conical
flask containing 2 mmol metal chloride dissolved in
20 cm3 of methanol while stirring. Water was added
dropwise under continuous stirring to the reaction mix-
ture. To complete the reaction, stirring was continued
for about 1 h. The resultant precipitate was separated
by filtration, washed several times with water and dried
in air. The complex was purified by dissolving it in ace-
tone, filtering and reprecipitating it by addition of water,
then separating by filtration.
2.1.2. Synthesis of 5-amino-4(4-chlorophenyl)-[1,2]
dithiole-3-thione
Yellow crystals of the new dithiol ligand (ACDT) of
appropriate dimensions suitable for X-ray diffraction
analysis were obtained from a slow evaporation of a

2946
H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
water solution of the ligand Na2CCPD Æ 2H2O and lan-
thanum chloride heptahydrate (LaCl3 Æ 7H2O).
2.2. Physical measurements and determinations
Elemental analyses, melting points, molar conductiv-
ities in nitromethane, magnetic susceptibility measure-
ments, infrared and electronic spectra were determined
as described before [10c]. The compounds prepared,
their elemental analyses and some other data are listed
in Tables 1 and 2.
2.1.3. Synthesis of mixed-ligand nickel(II) chelates
The new compounds [Ni(enR) S2C@C(CN)Y]
(Y = CN,Ph, COOEt, CONH2) were prepared accord-
ing to the following general method.
To a methanolic solution (ꢂ40 cm3) containing
5 mmol of the nitrogenous base, enR, an equimolar
amount of the 1,1-dithiolate salt was added. Upon dis-
solution the mixture was transferred dropwise to a
100 ml conical flask containing 5 mmol NiCl2 Æ 6H2O
dissolved in ꢂ20 cm3 of methanol while stirring contin-
uously. To complete the reaction the stirring was contin-
ued for 1 h and then was left undisturbed for a while.
The resultant precipitate was separated by filtration
and transferred to a beaker. Mixing with water and sub-
sequent filtration ensured removal of unreacted reagents
and inorganic salts. The solid product was washed sev-
eral times with water and finally with a small volume
of cold methanol, and then air dried.
2.3. X-ray single crystal structure determination of
(n-Bu4N)2[Cu(CCPD)2], [Ni(bipy)CPD] and ACDT
The data were collected using a STOE Imaging plate
diffraction system (IPDS) equipped with Mo Ka radia-
tion. The structure solution was performed with
SHELXS-97 [13] and structure refinement was done
against F2 using SHELXL-97 [14]. All non-hydrogen atoms
were refined using anisotropic displacement parameters.
The hydrogen atoms were positioned with idealized
˚
geometries (dC–H = 0.95 A), and refined with fixed iso-
tropic displacement parameters according to the riding
Table 1
Elemental analyses and physicochemical data of some (R4N)2[M(S2C@C(CN)Y)2] (M = Ni(II), Cu(II)) chelates
Compound
Color
Yield (%) M.p.a (ꢁC) Mw
C%
H%
N%
KM (S cm2 molꢀ1
)
1
2
3
4
5
6
7
8
(n-Bu4N)2 [Ni(CCPD)2]
(n-Bu4N)2 [Ni(CPD)2]
(n-Bu4N)2 [Ni(CED)2]
(n-Bu4N)2 [Ni(CCED)2]
(n-Bu4N)2 [Cu(CCPD)2]
(n-Bu4N)2 [Cu(CPD)2]
(Et4N)2 [Cu(CED)2]
light green
deep green
brown
green-yellow 78
yellow 90
brown-green 87
85
75
80
191–193
176–178
81–83
220–222
110–112
78–82
995.00 60.5 (60.35)b 8.2 (8.10)
5.5 (5.63)
164
926.21 65.2 (64.84)
918.14 57.4 (57.56)
860.06 55.6 (55.86)
999.86 60.1 (60.06)
931.04 64.3 (64.50)
698.54 47.9 (48.14)
864.89 55.7 (55.55)
9.10 (8.92) 5.92 (6.05) 155
9.05 (9.00) 6.00 (6.10) 152
8.75 (8.91) 9.86 (9.77) 168
7.9 (8.07)
5.5 (5.60)
170
8.80 (8.88) 5.90 (6.02) 153
7.00 (7.22) 7.87 (8.02) 154
8.67 (8.86) 9.58 (9.72) 160
brown-red
91
93
145–148
140–143
(n-Bu4N)2 [Cu(CCED)2] light brown
CED = 1-cyano-1-carboethoxy-2,2-ethylenedithiolate.
CPD = 1-cyano-1-phenyl-2,2-ethylenedithiolate.
CCED = 1-cyano-1-carboamido-2,2-ethylenedithiolate.
a
Decomposition.
Calculated values in parentheses.
b
Table 2
Elemental analyses and physicochemical data of some [Ni(enR)(S2C@C(CN)Y)] chelates
Compound
Color
Yield (%)
M.p.a (Cꢁ)
Mr
C%
H%
N%
leff (mB)
1
2
3
4
5
6
7
8
9
[Ni(dipyamH)i-MNT]
[Ni(bipy)CPD]
deep brown
deep red-brown
brown-green
deep green
light brown
orange
brown
light brown
deep red
90
83
76
77
80
74
68
80
76
75
60
271–275
280–284
245–248
340–345
231–235
288–292
257–260
294–296
304–306
308–312
315–318
370.10
406.15
364.18
421.19
486.30
360.14
458.25
354.09
402.14
417.16
388.12
45.2 (45.43)b
55.8 (56.19)
49.9 (49.47)
54.3 (54.18)
53.3 (54.34)
39.8 (40.02)
51.9 (52.42)
40.5 (40.70)
47.6 (47.79)
41.9 (42.07)
43.0 (43.32)
2.44 (2.45)
3.18 (3.23)
5.31 (5.26)
3.28 (3.35)
5.17 (5.18)
5.09 (5.32)
4.58 (4.63)
3.74 (3.70)
3.19 (3.26)
3.29 (3.38)
2.73 (2.86)
18.8 (18.92)
10.5 (10.35)
11.7 (11.54)
13.4 (13.30)
8.67 (8.64)
11.5 (11.67)
9.26 (9.17)
12.0 (11.87)
10.5 (10.45)
13.3 (13.43)
17.9 (18.05)
diam
1.71
2.19
1.82
diam
2.52
diam
diam
diam
diam
diam
[Ni(C · NN)CPD]
[Ni(dipyamH)CPD]
[(Ni(BenB)CED]
[Ni(C · NN)CED]
[Ni(PhenPh)CED]
[Ni(ampy)CED]
[Ni(bipy)CED]
[Ni(dipyamH)CED]
[Ni(dipyamH)CCED]
10
11
light brown
light brown
i-MNT = 1,1-dicyano-2,2-ethylenedithiolate.
a
Decomposition.
Calculated values in parentheses.
b

H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
2947
Table 3
Selected crystal data and experimental details for the structural study of ACDT (1), (n-Bu4N)2[Cu(CCPD)2] (2) and [Ni(bipy)CPD] (3)
1
2
3
Formula
C9H6NClS3
259.78
triclinic
[Cu(C9H4NS2Cl)2] Æ 2C16H36
999.86
triclinic
N
NiC19H13N3S2
406.15
monoclinic
P21/n
6.9292(5)
13.090(1)
18.667(2)
90.00
94.61(1)
90.00
1687.7(2)
170
MW (g molꢀ1
)
Crystal system
Space group
ꢀ
ꢀ
P1
P1
˚
a (A)
7.3401(6)
13.476(2)
16.189(2)
86.59(1)
89.74(1)
89.84(1)
1598.5(2)
170
9.523(1)
9.908(1)
15.830(1)
83.99 (1)
72.91(1)
71.93(1)
1357.2(2)
170
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Temperature (K)
Z
6
1
4
Dcalc (g cmꢀ3
F(000)
)
1.619
792
1.223
535
1.598
832
2h Range (ꢁ)
h/k/l Ranges
3–56
3–56
3–50
ꢀ9/9
ꢀ12/12
ꢀ13/13
ꢀ20/20
0.69
ꢀ8/6
ꢀ17/17
ꢀ21/21
0.9
ꢀ13/15
ꢀ22/22
1.40
l (Mo Ka) (mmꢀ1
)
Measured reflections
Rint
14939
0.0357
7582
6365
380
19675
0.0245
5895
5362
277
8807
0.0825
2974
2011
226
Independent refl.
Reflections with I > 2r(I)
Parameters
R1 [I > 2r(I)]
wR2 [all data]
Goodness-of-fit
0.0339
0.0936
1.018
0.33/ꢀ0.44
0.0445
0.1198
1.060
1.59/ꢀ1.20
0.0404
0.0902
0.945
0.40/ꢀ0.51
ꢀ3
˚
Residual electron density (e A
)
model [Uiso = 1.2 · Ueq(C)]. A special feature of the
refinement is that in (n-Bu4N)2[Cu(CCPD)2] some car-
bon atoms of the 6-membered aromatic ring which is at-
tached to the chloro atom and the chloro atom itself
shows some disordering. However, no reasonable split
models were found. Selected crystal data and results of
the structure refinement as well as bond lengths and an-
gles are found in Tables 3, 8, 9 and 10.
susceptibilities indicate 2:1 type electrolytes, mononu-
clear compounds.
The concurrent reaction of nickel with equimolar
quantities of nitrogenous bases, enR, and the 1,1-
dithiolato anions, (S2C@C(CN)Y)2ꢀ, affords neutral
mixed-ligand compounds corresponding to the general
formula [Ni(enR)S2C@C(CN)Y] (Y = CN, Ph, COOEt,
CONH2). The compounds are almost insoluble in
methanol, ethanol and acetone while their solubility in
dimethylformamide (DMF) and dimethylsulfoxide
(DMSO) is considerable. Their low electrical conduc-
tance values (Km ꢃ 15 S cm2 molꢀ1) in DMF and their
solid state magnetic susceptibility indicate neutral,
mononuclear diamagnetic compounds and only the
compounds of the [Ni(enR)CPD] series were found to
be paramagnetic with magnetic moments, leff, in the
range 1.7 to 2.3 mB. This behavior in the solid state mer-
its some comments. It is well known that nickel(II) has a
tendency to achieve coordination numbers exceeding
four by accepting ligands in the vacant coordination
sites, or by aggregation of the parent compounds
[10b,15]. Ligands with sulfur donor atoms may instigate
intermolecular interactions of the type M–Sꢁ ꢁ ꢁM,
provided that the arrangement of the monomers in the
unit cell permits such interactions. For instance, the
molecules in the unit cell of [Ni(bipy)CPD] are arranged
3. Results and discussion
The simultaneous reaction of nickel(II) or cop-
per(II) with 1,1-dithiolato anions (S2C@C(CN)Y)2ꢀ
and tetrabutylammonium bromide (n-Bu4NBr) or
tetraethylammonium bromide (Et4NBr) in a 1:2:2
molar ratio, respectively, produces compounds corre-
sponding to the general formulas [R4N]2[M(S2C@C
(CN)Y)2], (R = n-Bu, Et, M = Ni(II), Cu(II), Y =
phCl (CCPD), ph (CPD), COOEt (CED), CONH2-
(CCED)). The new chelates are insoluble in water
and soluble in organic solvents. The copper(II) com-
plexes are paramagnetic with magnetic moments, leff,
in the range 1.65–1.82 mB and the nickel(II) complexes
are diamagnetic. Their electrical conductance values in
nitromethane (Table 1) and their solid state magnetic

2948
H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
in pairs as shown in Fig. 1(a). Each pair of molecules
lato ligands [18–22]. This notion is supported by the
change in the magnetic behavior of [Ni(bipy)CPD], ob-
served when magnetic susceptibility measurements were
performed in solutions. This compound is sufficiently
soluble in acetone permitting the determination of vmol
by Evansꢀ method. The propensity towards aggregation
in the [Ni(enR)CPD] complexes is probably due to the
residual Lewis acidity of the nickel atoms as well as
the basicity of the sulfur atoms. Further information
form two weak intermolecular Niꢁ ꢁ ꢁS bond interactions
˚
at a distance of 3.617 A (Fig. 1(b)). According to the
classic paper by Bondi [16], the sum of the van der
˚
Waals radii of nickel and sulfur is 3.4 A. There is wide
agreement that this is an underestimation [17,18]. The
Paramagnetism of solid [Ni(bipy)CPD] suggests the
same arrangement of the monomers and long range
interactions, not uncommon in compounds with dithio-
a
b
c
a
Ni1
b
a
c
N3
Ni1
b
N2
3.897
C11
3.986
3.741
3.542
3.617
S1
S2
Fig. 1. (a) The arrangement of the molecules in the unit cell of [Ni(bipy)CPD]. (b) A pair of molecules showing the intermolecular distances.
Table 4
Wavenumbers of characteristic bands in the IR spectra of some (R4N)2[M(S2C@C(CN)Y)2] (M = Ni, Cu) chelates
Compound
m(C„N)
m(C@O)
m(C@CS2)
mas(CSS)
ms (CSS)
m(Ni–S)
1
2
3
4
5
6
7
8
(n-Bu4N)2[Ni(CCPD)2]
(n-Bu4N)2[Ni(CPD)2]
(n-Bu4N)2[Ni(CED)2]
(n-Bu4N)2[Ni(CCED)2]
(n-Bu4N)2[Cu(CCPD)2]
(n-Bu4N)2[Cu(CPD)2]
(Et4N)2[Cu(CED)2]
2179(vs)
2180(vs)
2188(s)
1389(s)
905(m)
905(s)
920(s)
910(m)
907(m)
910(sh)
928(s)
918(s)
880(m)
882(m)
390(m)
1427(vs)
1395(vs)
1425(vs)
1411(vs)
1418(vs)
1390(sh)
1421(vs)
391(m), 376(s)
383(w), 340(vw)
387(m)
368(m)
410(m), 335(w)
335(m)
1673(vs)
1640(vs)
2188(s)
878(m)
876(s)
890(s)
907(s)
872(s)
2185(vs)
2178(vs)
2195(vs)
2192(vs)
1660(sh),1678(vs)
1640(vs)
(n-Bu4N)2[Cu(CCED)2]
350(m)
vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder; br, broad.

H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
2949
on the mode of interaction of the ligands and the struc-
ture of the compounds under consideration were ob-
tained from their IR and the electronic excitation
spectra.
The dianion of the 1,1-dithiol contains the C@CS2,
C„N and Y (Y = CN, Ph, phCl, COOEt, CONH2)
functional groups. The absorptions due to the multiple
bond in each group are immediately distinguishable
and identified with the very strong bands observed in
specific regions of the spectrum. For instance, in
K2S2C@C(CN)CONH2 the m(C„N) and m(C@O) bands
appear at 2172 and 1646 cmꢀ1, respectively, while the
m(C@CS2) band absorbs at 1340 cmꢀ1. Upon chelation
3.1. Infrared spectra
The infrared spectra of the complexes have been
interpreted in the light of earlier investigations [1a,10].
Table 5
Wavenumbers of the characteristic bands in the IR spectra of some mixed-ligand nickel(II) chelates, [Ni(enR)(S2C@C(CN)Y]
Compound
m(N–H)
(C„N)
m(C@O)
m(C@CS2)
mas(CS2)
ms(CS2)
m(Ni–N)
m(Ni–S)
1
2
3
4
5
6
7
8
9
[Ni(dipyamH)i-MNT]
[Ni(bipy)CPD]
[Ni(C · NN)CPD]
[Ni(dipyamH)CPD]
[Ni(BenB)CED]
[Ni(C · NN)CED]
[Ni(PhenPh)CED]
Ni(ampy)CED]
3295(s), 3250(m), 3200(s), 3140(s)
2206(vs)
2197(vs)
2192(vs)
2192(vs)
2206(s)
2222(s)
2212(s)
2195(vs)
2214(s)
2202(vs)
2210(vs)
1387(vs)
1438(vs)
1435(vs)
1438(vs)
1416(sh)
1395(sh)
1423(vs,br)
1419(sh)
1423(sh)
1421(sh)
1418(vs)
944(m)
903(m)
900(s,br)
908(vs)
920(s,br)
930(s,br)
932(s)
926(s)
928(s)
933(s)
918(m)
901(s)
470(m)
488(w)
483(m)
495(w)
458(m)
498(m)
518(m)
488(m)
483(w)
483(w)
478(w)
390(m)
405(w)
393(m)
393(w)
343(w)
388(m)
380(m)
343(m)
348(w)
378(w)
392(m)
3360(s), 3270(s)
3310(s), 3240(m), 3210(s), 3140(m)
3190(s), 3170(sh)
3360(s), 3255(s)
3180(s)
3300(s), 3210(sh)
1683(vs)
1673(vs)
1655(vs)
1688(vs)
1686(vs)
1656(vs)
1643(vs)
916(sh)
918(sh)
921(sh)
896(m)
[Ni(biby)CED]
[Ni(dipyamH)CED]
[Ni(dipyamH)CCED]
10
11
3310(s), 3250(m), 3210(s), 3150(m)
3300(s), 3250(m), 3200(s), 3140(m)
vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder; br, broad.
Table 6
Ligand field excitation bands in the electronic absorption spectra of some (R4N)2[M(S2C@C(CN)Y)2] (M = Ni, Cu) chelates
Ligand field bands (v (lmꢀ1))
~
Compound
Nujol
CH2Cl2
Pyridine
1
2
3
4
5
6
7
8
(n-Bu4N)2[Ni(CCPD)2]
(n-Bu4N)2[Ni(CPD)2]
(n-Bu4N)2[Ni(CED)2]
(n-Bu4N)2[Ni(CCED)2]
(n-Bu4N)2[Cu(CCPD)2]
(n-Bu4N)2[Cu(CPD)2]
(Et4N)2[Cu(CED)2]
1.57
1.645
1.66(sh)
1.580
1.56(sh)
1.63(sh)
1.60(sh)
1.55(sh)
1.58 (95)a
1.58 (98)
1.647 (250)
1.64(sh) (150)
1.590 (116)
1.56(sh) (450)
1.63(sh) (710)
1.61(sh) (670)
1.56(sh) (650)
1.642 (210)
1.65(sh) (160)
16.00 (110)
1.56(sh) (455)
1.650 (674)
1.61(sh) (510)
1.56(sh) (560)
b
(n-Bu4N)2[Cu(CCED)2]
a
Values of the molar extinction coefficient.
sh, shoulder.
b
Table 7
Ligand field excitation bands in the electronic absorption spectra of some mixed-ligand nickel(II) chelates, [Ni(enR)(S2C@C(CN)Y]
Compound
Ligand field bands (~v (lmꢀ1))
Nujol
DMSO
Pyridine
1.567 (47)a
1.54(sh) (44)
1.66(sh) (93)
1.767 (137)
1.75(sh) (68)
1.61(sh) (66)
1.59(sh) (65)
1.80(sh) (90)
1.72(sh) (130)
1.77(sh) (140)
1.61(sh) (60)
1.60(sh) (50)
1.113 (17)
b
1
2
3
4
5
6
7
8
9
[Ni(dipyamH)i-MNT]
[Ni(bipy)CPD]
[Ni(C · NN)CPD]
[Ni(dipyamH)CPD]
[Ni(BenB)CED]
[Ni(C · NN)CED]
[Ni(PhenPh)CED]
[Ni(ampy)CED]
1.77(sh)
1.72(sh)
1.55(sh)
1.76(sh)
1.75(sh)
1.55(sh)
1.64(sh)
1.77(sh)
1.72(sh)
1.87(sh)
1.80(sh)
1.76(sh) (125)
[Ni(bipy)CED]
[Ni(dipyamH)CED]
[Ni(dipyamH)CCED]
10
11
a
1.76(sh) (180)
1.59(sh) (55)
1.119 (16)
sh, shoulder.
b
Values of the molar extinction coefficient.

2950
H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
Fig. 2. Structure of [Cu(CCPD)2]2ꢀ, in the crystal with thermal ellipsoids at the 50% probability level.
of the dianions these bands are strongly shifted to higher
wavenumbers (Tables 4 and 5) since in these planar li-
gands the extensive p-conjugated system permits a drift
of electron density towards the sulfur atoms that results
in a shortening of the C„N, C@O and C@C bonds. The
exact frequency of each band is influenced not only by
the groups present in the 1,1-dithiolato dianion, but also
by the donor strength of the chelated nitrogenous base.
Actually, the frequency of the m(C@O) vibration in the
chelates [Ni(PhenPh)CED], [Ni(dipyam)CED], and in
the complexes of the dithiolate CCED coincides with
that of the corresponding free 1,1-dithiolato dianion,
probably because of the enhanced double bond charac-
ter of the bond between the carbonylic carbon atom and
the oxygen and nitrogen atoms of the OEt and NH2
groups. The asymmetric and symmetric stretching vibra-
tions of the @CS2 group generally appear in the 945–900
and the 920–870 cmꢀ1 regions, respectively. The
stretching vibration of the M–S bond is observed at
Table 8
˚
Selected bond lengths (A) and bond angles (ꢁ) of (n-Bu4N)2
[Cu(CCPD)2]
˚
Bond lengths (A)
Cu(1)–S(2A)
Cu(1)–S(1A)
Cl(1)–C(4)
S(2)–C(8)
C(1)–C(7)
C(7)–C(9)
Cu(1)–S(2)
Cu(1)–S(1)
S(1)–C(8)
2.195(1)
2.213(1)
1.752(2)
1.743(2)
1.479(3)
1.437(3)
2.195(1)
2.213(1)
1.755(2)
1.154(3)
1.378(3)
370( 30) cmꢀ1
.
The absorptions occurring in the region ꢂ3300 to
3200 cmꢀ1 are due to the N–H stretching vibrations of
partially substituted 1,2-diamines and are shifted to
wavenumbers lower than those encountered in the free
1,2-diamines [23]. These shifts and the band near
490( 30) cmꢀ1 suggest that the nitrogenous bases che-
late, as expected. Bidentate coordination and chelation
N(1)–C(9)
C(7)–C(8)
Bond angles (ꢁ)
S(2A)–Cu(1)–S(1A)
S(2A)–Cu(1)–S(1)
C(8)–S(1)–Cu(1)
C(6)–C(1)–C(7)
C(4)–C(3)–C(2)
C(3)–C(4)–Cl(1)
C(8)–C(7)–C(9)
C(9)–C(7)–C(1)
C(7)–C(8)–S(1)
N(1)–C(9)–C(7)
S(2)–Cu(1)–S(1A)
S(2)–Cu(1)–S(1)
C(8)–S(2)–Cu(1)
C(2)–C(1)–C(7)
C(3)–C(4)–C(5)
C(5)–C(4)–Cl(1)
C(8)–C(7)–C(1)
C(7)–C(8)–S(2)
S(2)–C(8)–S(1)
78.39(2)
101.61(2)
87.6(1)
120.4(2)
119.9(2)
119.5(2)
116.0(2)
115.4(2)
124.6(2)
177.5(2)
101.61(2)
78.39(2)
88.5(1)
123.2(2)
120.3(2)
120.2(2)
128.6(2)
129.8(2)
105.5(1)
Fig. 3. Structure of ACDT in the crystal with thermal ellipsoids at the
50% probability level.

H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
2951
of the dianion of the 1,1-dithiol suggest the band at
370( 30) cmꢀ1 and the bands due to the asymmetric
and symmetric vibrations of the @CS2 fragment
(Tables 4, 5).
different donor ability. Because of the low solubility of
the majority of the mixed-ligand complexes, polar sol-
vents with appreciable donor strength were used to ob-
tain the solution spectra. The most interesting feature
of these spectra is the band in the region 1.55–
1.66 lmꢀ1 and for mixed-ligand complexes 1.55–
1.87 lmꢀ1 (Tables 6 and 7), which may be ascribed to
a ligand field (LF) transition for reasons of intensity
and energetic considerations.
3.2. Electronic excitation spectra
The electronic excitation spectra of the chelates were
studied in the visible and the near-infrared region, in the
solid state and in solution employing solvents with very
The energy of the LF band of the homoleptic com-
plexes depends slightly on the nature of dithiolate li-
gands. The dithiolate ligand field strength (CCPD ꢂ
CCED < CED ꢂ CPD) is related to the ability of their
substituents Y to resist electron drift towards the sulfur
atoms. The LF band of the complexes has almost the
same energy, both in their solid state spectra and those
employing solvents with different donor ability (CH2Cl2,
DMSO, CH3CN and pyridine). This is probably due to
the nucleophilic interaction of the polar solvent mole-
cules with the ligand, leaving the metal unaffected.
In the solid state spectra of the mixed-ligand chelates,
the change in the excitation energy may be accounted
for by taking into consideration the influence of the sub-
stituents Y on the strength of the ligand field (LF) in the
chelates [Ni(dipyamH)S2C@C(CN)Y]. In the diamag-
netic compounds of the dianions i-MNT, CCED and
CED, the LF excitation energy reflects the ability of
the Y group to resist electron delocalization towards
their sulfur atoms (i-MNT P CCED > CED). The low
LF excitation energy of [Ni(dipyamH)CPD] is not con-
sistent with the above explanation since the electron
withdrawing ability of the phenyl group is rather re-
stricted. However, the magnetic behavior of the
[Ni(enR)CPD] chelates is at variance with the behavior
of the other nickel(II) chelates and suggests intermolec-
ular interactions, presumably along the z axis, that
change the symmetry of the field in which the nickel(II)
Table 9
˚
Selected bond lengths (A) and bond angles (ꢁ) of ACDT with e.s.d.s in
parentheses
˚
Bond lengths (A)
S(1)–C(1)
S(2)–C(3)
Cl(1)–C(7)
C(1)–C(2)
C(2)–C(4)
S(1)–S(2)
S(3)–C(1)
N(1)–C(3)
C(2)–C(3)
1.737(2)
1.748(2)
1.747(2)
1.404(3)
1.491(2)
2.070(1)
1.688(2)
1.338(3)
1.396(2)
Bond angles (ꢁ)
C(1)–S(1)–S(2)
C(2)–C(1)–S(3)
S(3)–C(1)–S(1)
C(3)–C(2)–C(4)
N(1)–C(3)–C(2)
C(2)–C(3)–S(2)
C(5)–C(4)–C(2)
C(8)–C(7)–Cl(1)
C(3)–S(2)–S(1)
C(2)–C(1)–S(1)
C(3)–C(2)–C(1)
C(1)–C(2)–C(4)
N(1)–C(3)–S(2)
C(9)–C(4)–C(2)
C(6)–C(7)–Cl(1)
96.8(1)
130.9(2)
114.0(1)
120.9(2)
125.1(2)
117.5(2)
120.8(2)
119.0(2)
93.6(1)
115.1(2)
116.9(2)
122.1(2)
117.4(2)
120.1(2)
119.5(2)
Fig. 4. Structure of [Ni(bipy)CPD] in the crystal with thermal ellipsoids at the 50% probability level.

2952
H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
exists. The existence of axial donor-acceptor interactions
is supported by the red shift of the LF band of the other
[Ni(dipyamH)(S2C@C(CN)Y)] chelates when the
absorption spectra are obtained in solvents of enhanced
donicity and the appearance of an additional band at
ꢂ1.1 lmꢀ1, when employing pyridine as solvent. In the
case of the compound [Ni(dipyam)CPD] the energy of
the LF excitation remains unaltered upon dissolution
in DMSO or pyridine. This suggests that the axial
Sꢁ ꢁ ꢁNiꢁ ꢁ ꢁS interactions that are eliminated upon dissolu-
tion are compensated by the nickel–solvent interactions.
The strength of the field applied by the nitrogenous
base is nicely mirrored in the energy of the LF bands
in the [Ni(enR)CED] chelates. The weak donating abil-
ity of dipyamH does not contribute significantly to the
electron density on the nickel atom thus permitting
coordination of strong polar molecules, i.e. pyridine or
DMSO. On the other hand, the powerful electron donor
C · NN upon ligation increases the electron population
on the sulfur atoms. Consequently, the intermolecular
axial interactions are enhanced while the energy of the
transitions within the d manifold diminishes. The inter-
molecular interactions explain the magnetic behavior of
the [Ni(enR)S2C@(CN)Y] chelates and the blue shift ob-
served upon dissolution when the axial interactions are
disrupted. In the case of compounds with nitrogenous
bases possessing intermediate donor ability, such as bipy
and BenB, the energy of the LF transition is the same in
solution and in the solid state. Proof that the NiN2S2
chromophore is planar was acquired from the X-ray
structure determination of [Ni(bipy)CPD].
state, with the shortest distances being 10.366 and
9.523 A, respectively. This feature might be a result of
the electronic effects and the unit cell packing caused
by the bulky quaternary ammonium cations which occu-
py much of the space and prevent any intermolecular
Cu–S or Cu–Cu interaction [21a].
˚
3.2.2. Description of the structure of ACDT
A thermal ellipsoid drawing of the novel sulfur-rich
ligand is presented in Fig. 3. The selected bond lengths
Table 10
˚
Selected bond lengths (A) and angles (ꢁ) for [Ni(bipy)CPD] (e.s.d.s are
given in parentheses)
˚
Bond lengths (A)
Ni(1)–N(2)
Ni(1)–S(2)
S(1)–C(8)
1.915(3)
2.173(2)
1.741(4)
1.149(5)
1.367(6)
1.362(5)
1.464(6)
1.351(6)
1.923(3)
2.188(2)
1.750(3)
1.486(5)
1.442(6)
1.364(5)
1.346(5)
1.392(5)
N(1)–C(9)
C(7)–C(8)
N(2)–C(11)
C(15)–C(16)
N(3)–C(16)
Ni(1)–N(3)
Ni(1)–S(1)
S(2)–C(8)
C(1)–C(7)
C(7)–C(9)
N(2)–C(15)
N(3)–C(20)
C(16)–C(17)
Bond angles (ꢁ)
N(2)–Ni(1)–N(3)
N(3)–Ni(1)–S(2)
N(3)–Ni(1)–S(1)
C(8)–S(1)–Ni(1)
C(6)–C(1)–C(7)
C(8)–C(7)–C(9)
C(9)–C(7)–C(1)
C(7)–C(8)–S(2)
N(1)–C(9)–C(7)
C(11)–N(2)–Ni(1)
C(15)–N(2)–Ni(1)
N(2)–C(15)–C(16)
C(20)–N(3)–C(16)
C(16)–N(3)–Ni(1)
N(3)–C(16)–C(15)
N(2)–Ni(1)–S(2)
N(2)–Ni(1)–S(1)
S(2)–Ni(1)–S(1)
C(8)–S(2)–Ni(1)
C(2)–C(1)–C(7)
C(8)–C(7)–C(1)
C(7)–C(8)–S(1)
83.4(2)
98.0(2)
176.2(2)
88.8(2)
3.2.1. Description of the structure of (n-Bu4N)2-
[Cu(CCPD)2]
119.6(4)
115.1(3)
115.8(4)
124.5(3)
179.0(5)
126.9(3)
114.9(3)
112.9(4)
118.8(3)
114.4(2)
114.2(3)
178.5(2)
100.4(1)
78.2(1)
The structure of the anion is shown in Fig. 2, while
selected bond lengths and angles are given in Table 8.
There are three molecules per unit cell. The copper atom
lies on a crystallographic center of symmetry which re-
quires the CuS4 unit to be strictly planar. This plane
forms a small dihedral angle (1.35ꢁ) with the best plane
through the S2C@C–CN fragment of the CCPD ligand.
This conformation has been observed in many sulfur
chelates which contain a planar MS4 group [24,6c].
The plane of the phenyl ring makes an angle of 8.87ꢁ
with the CuS4 plane. The average Cu–S bond length
˚
(2.204 A) in the present structure is shorter by
89.0(2)
˚
ꢂ0.099 A to that reported [21a] for the only other
122.7(4)
129.2(3)
131.5(3)
104.0(2)
118.1(4)
121.9(4)
121.7(4)
125.2(4)
126.7(3)
121.4(4)
122.2(5)
four-coordinated, S-bonded Cu(II) complex with a 1,1-
˚
dithiolate chelate, (2.303 A) in [Bu4N]2[Cu(i-MNT)2],
S(1)–C(8)–S(2)
which most probably accounts for the different ability
of the ph-Cl and C„N groups of the dithiolate ligands
to resist the electron delocalization towards the sulfur
atoms. A distorted square planar coordination environ-
ment around the copper ion is evident in the S–Cu–S an-
gles, 78.39(2)ꢁ and 101.61(2)ꢁ, respectively. There is no
intermolecular Cu–S or Cu–Cu interaction in the solid
C(11)–N(2)–C(15)
N(2)–C(15)–C(14)
N(2)–C(11)–C(12)
C(14)–C(15)–C(16)
C(20)–N(3)–Ni(1)
N(3)–C(16)–C(17)
N(3)–C(20)–C(19)

H.H. Alkam et al. / Polyhedron 24 (2005) 2944–2954
2953
Table 11
˚
Experimental average bond lengths (A) of some [Ni(enR)S2C@C(CN)Y] chelates
˚
Compound
Average bond distance (A)
Ref.
ÆS2C@Cæ
ÆC–Sæ
ÆNi–Sæ
ÆNi–Næ
1
2
3
4
[Ni(Et2en)i-MNT]
[Ni(Et2en)CPD]
[Ni(bipy)CPD]
1.384(3)
1.367(3)
1.367(6)
1.366(5)
1.716(3)
1.741(3)
1.746(3)
1.733(3)
2.199(8)
2.179(1)
2.181(2)
2.178(1)
1.955(2)
1.965(2)
1.919(3)
1.974(3)
[10a]
[28]
this work
[28]
[Ni(Me4en)CPD]
and angles are given in Table 9. There are three crystal-
lographically independent molecules in the asymmetric
unit which differ in the torsion angles between both
rings. Three carbon atoms link with two sulfur atoms
forming a five-membered ring. The observed C–S dis-
tances are smaller than expected for a C–S single bond
that an electron drift from the X and Y substituent
groups of the 1,1-dithiolato ligands towards the sulfur
atoms takes place and becomes more intense in the case
of the CPD chelate. Consequently, the intensity of the
nickel–nitrogen interaction diminishes.
˚
(1.82 A) [25]. The exocyclic S3–Cl bond length is
˚
1.688(2) A which is longer than the corresponding dis-
4. Supplementary material
˚
tance of 1.661(8) A in dmit ligand [4b] but shorter than
the distance found in another dmit ligand [18a]. The S–S
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre, CCDC Nos.
236938–236940 for compounds ACDT, (n-Bu4N)2
[Cu(CCPD)2], [Ni(bipy)CPD], respectively. Copies of
the data can be obtained free of charge on application
to The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK, fax: +44 1223 366 033, e-mail: deposit@
ccdc.ac.uk or on the web www: http://www.ccdc.
cam.ac.uk.
˚
bond distance, 2.070(1) A, is within the normal range
˚
(2.007(3)–2.396(3) A) found for sulfur-rich dithiolate
metal complexes [21a]. The C1–C2 bond length,
˚
1.404(3) A, is similar to the corresponding bond dis-
tances in salts of the i-MNT ligand [26]. All observed
intramolecular bond lengths in the sulfur ring indicate
delocalization of the p-electron system.
3.2.3. Description of the structure of [Ni(bipy)CPD]
In the unit cell there are six nickel atoms (Fig. 1(a)).
In the immediate vicinity of each nickel atom exist two
sulfur and, at shorter distance, two nitrogen atoms
(Fig. 4). The sulfur atoms of the dianion of 1,1-dithiol
form a bite angle of 78.2(1)ꢁ while the bite angle of
the 2,20-bipyridine is 83.4(2)ꢁ and reaffirm that the
bidentate ligands chelate. Intramolecular bond distances
and angles are given in Table 10. The nitrogen atoms are
in the plane defined by nickel and the sulfur atoms. In
the same plane lie the atoms of the ethene group and
the cyano group. The phenyl group, however, forms a
dihedral angle of 17.5ꢁ with the plane of the NiN2S2
chromophore probably because of steric and electronic
effects. The S2C@C–CN fragment of the ligand (CPD)
assumes a planar conformation and the bond distances
indicate extensive p-conjugation. Actually the C(8)–
C(7) distance is characteristic of a bond localized be-
tween two C(sp2) atoms [27], whilst the lengths of the
intervening C(7)–C(9) bond and the terminal N„C
bond suggest delocalization. The mean deviation of
Acknowledgments
The efforts and cooperation of Professor Dr. Wolf-
gang Bensch, The Director of the Institute of Inorganic
Chemistry, Christain–Albrechts University of Kiel in
Germany, are highly appreciated and acknowledged.
We are also very grateful for Dr. Christian Na¨ther and
Inke Jeß from the University of Kiel for the structure
determination of ACDT, (n-Bu4N)2[Cu(CCPD)2] and
[Ni(bipy)CPD].
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