Novel octahedral nickel(II) dithiocarbamates with bi- or tetradentate N-donor ligands: X-ray structures of [Ni(Bzppzdtc)(phen)2]ClO4 · CHCl3 and [Ni(Bz2dtc)2(cyclam)]

Article abstract of DOI:10.1016/j.poly.2007.09.024

A series of novel octahedral nickel(II) dithiocarbamate complexes involving bidentate nitrogen-donor ligands (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine) or a tetradentate ligand (cyclam = 1,4,8,11-tetraazacycloteradecane) of the composition [Ni(BzMetdtc)(phen)₂]ClO₄ (1), [Ni(Pe₂dtc)(phen)₂]ClO₄ (2), [Ni(Bzppzdtc)(phen)₂]ClO₄ · CHCl₃ (3), [Ni(Bzppzdtc)(phen)₂](SCN) (4), [Ni(BzMetdtc)(bpy)₂]ClO₄ · 2H₂O (5), [Ni(Pe₂dtc)(cyclam)]ClO₄ (6), [Ni(BzMetdtc)₂(cyclam)] (7), [Ni(Bz₂dtc)₂(cyclam)] (8) and [Ni(Bz₂dtc)₂(phen)] (9) (BzMetdtc = N,N-benzyl-methyldithiocarbamate(1-) anion, Pe₂dtc = N,N-dipentyldithiocarbamate(1-) anion, Bz₂dtc = N,N-dibenzyldithiocarbamate(1-) anion, Bzppzdtc = 4-benzylpiperazinedithiocarbamate(1-) anion), have been synthesized. Spectroscopic (electronic and infrared), magnetic moment and molar conductivity data, and thermal behaviour of the complexes are discussed. Single crystal X-ray analysis of 3 and 8 confirmed a distorted octahedral arrangement in the vicinity of the nickel atom with a N₄S₂ donor set. They represent the first X-ray structures of such type complexes. The catalytic influence of complexes 2, 3, 6, and 7 on graphite oxidation was studied and discussed.

Full text of DOI:10.1016/j.poly.2007.09.024

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 411–419
www.elsevier.com/locate/poly
Novel octahedral nickel(II) dithiocarbamates with bi- or tetradentate
N-donor ligands: X-ray structures
of [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 and [Ni(Bz2dtc)2(cyclam)]
a,
a
b
*
´ ´ˇ
´
´
Zdeneˇk Travnıcek , Richard Pastorek , Vaclav Slovak
a
Department of Inorganic Chemistry, Faculty of Science, Palacky´ University, Krˇı´zˇkovske´ho 10, CZ-771 47 Olomouc, Czech Republic
b
Department of Chemistry, Faculty of Science, University of Ostrava, 30. dubna 22, CZ-701 03 Ostrava, Czech Republic
Received 12 July 2007; accepted 28 September 2007
Available online 5 November 2007
Abstract
A series of novel octahedral nickel(II) dithiocarbamate complexes involving bidentate nitrogen-donor ligands (phen = 1,
10-phenanthroline, bpy = 2,20-bipyridine) or a tetradentate ligand (cyclam = 1,4,8,11-tetraazacycloteradecane) of the composition
[Ni(BzMetdtc)(phen)2]ClO4 (1), [Ni(Pe2dtc)(phen)2]ClO4 (2), [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3), [Ni(Bzppzdtc)(phen)2](SCN) (4),
[Ni(BzMetdtc)(bpy)2]ClO4 Æ 2H2O (5), [Ni(Pe2dtc)(cyclam)]ClO4 (6), [Ni(BzMetdtc)2(cyclam)] (7), [Ni(Bz2dtc)2(cyclam)] (8) and
[Ni(Bz2dtc)2(phen)] (9) (BzMetdtc = N,N-benzyl-methyldithiocarbamate(1-) anion, Pe2dtc = N,N-dipentyldithiocarbamate(1-) anion,
Bz2dtc = N,N-dibenzyldithiocarbamate(1-) anion, Bzppzdtc = 4-benzylpiperazinedithiocarbamate(1-) anion), have been synthesized.
Spectroscopic (electronic and infrared), magnetic moment and molar conductivity data, and thermal behaviour of the complexes are
discussed. Single crystal X-ray analysis of 3 and 8 confirmed a distorted octahedral arrangement in the vicinity of the nickel atom with
a N4S2 donor set. They represent the first X-ray structures of such type complexes. The catalytic influence of complexes 2, 3, 6, and 7 on
graphite oxidation was studied and discussed.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Nickel(II); Dithiocarbamates; X-ray structures; Graphite oxidation
1. Introduction
also found that [Ni(Et2dtc)2] (Et = ethyl) forms adducts
with pyridine and c-picoline at liquid nitrogen temperature.
The same conclusion was also confirmed by Dingle [2].
On the contrary, Ramalingam and co-workers [3] were
unsuccessful in the preparation of pyridine and ethylenedi-
amine (en) adducts of [Ni(Et2dtc)2], [Ni(HEadtc)2] and
[Ni(Ea2dtc)2] (H2Eadtc = ethanoldithiocarbamic acid).
They had only found that in the case of attempts to prepare
the discussed adducts with ethylenediamine, the reactions
led to the formation of [Ni(en)3]2+[(dtc)2]2ꢀ and/or [Ni-
(en)3]S2O3, respectively.
Generally, it is well known that square-planar dithiocar-
bamates (dtc) of nickel(II) of the type [Ni(dtc)2] react very
unreadily with nitrogen-donor ligands. To date, only a few
data regarding this topic have been found in the literature.
For instance, Coucouvanis and Fackler [1] studied reac-
tions of the mentioned Ni(II)-dithiocarbamates with mono-
dentate N-donor ligands and synthesized paramagnetic
octahedral complexes [Ni(H2dtc)2(c-pic)2], [Ni(H2dtc)2-
(py)2] and [Ni(HRdtc)2(c-pic)2] (R = chlorophenyl; c-
pic = c-picoline, py = pyridine). Moreover, the authors
Formerly, as a continuation in our systematic study of
dithiocarbamate transition metal complexes, especially of
nickel, we have prepared and characterized a binuclear
complex {[Ni(Ea2dtc)2]2(l-en)} in which two nickel(II) ions
*
Corresponding author. Tel.: +420 58 5634350; fax: +420 58 5634352.
´
´ˇ
E-mail address: zdenek.travnicek@upol.cz (Z. Travnıcek).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.09.024

412
Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
are connected via an ethylenediamine bridge [4]. We have
also synthesized octahedral [Ni(BziPrdtc)2(cyclam)] and
[Ni(BziPrdtc)(cyclam)]X complexes, where cyclam = 1,4,
8,11-tetraazacyclodecane, BziPrdtc = N,N-benzylisopropyl-
dithiocarbamate, (X = ClO4, BPh4) [5]. Moreover, the
[Ni(BziPrdtc)(cyclam)]BPh4 Æ CHCl3 complex has been
structurally characterized by single crystal X-ray analysis.
In search for X-ray structures deposited within the
Cambridge Structural Database [6] involving any transi-
tion metal in combination with a dithiocarbamate moiety
and any N-donor ligand, and bearing a N4S2 donor set,
ten molecular structures complying with the above-men-
tioned requirement have been found, i.e. four mononuclear
Ru(II) complexes [7–9], three dinuclear Mo(V) complexes
[10–12], two mononuclear Co(III) [13,14] complexes, and
one mononuclear Ni(II) complex [15].
In this paper, we report the synthesis and characteriza-
tion of novel octahedral Ni(II)-dithiocarbamate com-
plexes 1–9 along with the single crystal X-ray structures
of 3 and 8. Moreover, the methods of thermal analysis
have been used for the study of influence of selected
complexes on graphite oxidation. This possible practical
utilization of Ni(II)-dithiocarbamates have been also
described and discussed recently in case of similar com-
plexes [16,17].
2.2.2. [Ni(BzMetdtc)(phen)2]ClO4 (1) and
[Ni(BzMetdtc)(bpy)2]ClO4 Æ 2H2O (5)
To a suspension of finely powdered [Ni(BzMetdtc)2]
(0.23 g, 0.5 mmol) in an ethanol/chloroform mixture (30/
30 mL), NiCl2 Æ 6H2O (0.11 g, 0.5 mmol), LiClO4 Æ 3H2O
(0.16 g, 1 mmol) and bpy (0.31 g, 2 mmol) or phen
(0.39 g, 2 mmol) were added in this sequence. The reaction
mixture was stirred under reflux for 20 h and then filtered.
The solid formed after 5 days. It was filtered off, washed
with ethanol and diethyl ether, and recrystallized from a
chloroform solution with activated carbon. The substance
which formed, was filtered off, washed with diethyl ether
and dried under an infrared lamp at 40 ꢁC. Yields: 56%
(1) and 73% (5). Anal. Calc. for C33H26N5NiS2ClO4 (1):
C, 55.4; H, 3.7; N, 9.8; Ni, 8.2; S, 9.0; Cl, 5.0. Found: C,
54.9; H, 3.4; N, 9.5; Ni, 8.3; S, 8.8; Cl, 4.8%. Anal. Calc.
for C29H30N5NiS2ClO6 (5): C, 49.6; H, 4.3; N, 10.0; Ni,
8.3; S, 9.1; Cl, 5.0. Found: C, 49.8; H, 4.2; N, 10.2; Ni,
8.2; S, 8.9; Cl, 4.7%.
2.2.3. [Ni(Pe2dtc)(phen)2]ClO4 (2)
Phen (0.40 g, 2 mmol) and LiClO4 Æ 3H2O (0.16 g,
1 mmol) were added in this sequence to a suspension of
finely powdered [Ni(Pe2dtc)2] [8] (0.52 g, 1 mmol) in meth-
anol (15 mL). The reaction mixture was stirred under reflux
until the colour of the solution turned to red (2 h). Then,
the solution was filtered with activated carbon and the fil-
trate was left to stand at room temperature. After several
hours, crystals formed in the mother liquor from which sin-
gle crystals suitable for X-ray analysis were selected. The
remaining portion of the crystalline product was filtered
off, washed with methanol and diethyl ether and dried
under an infrared lamp at 40 ꢁC. Yield: 81%. Anal. Calc.
for C35H38N5NiS2ClO4 (2): C, 56.0; H, 5.1; N, 9.3; Ni,
7.8; S, 8.5; Cl, 4.7. Found: C, 56.1; H, 5.0; N, 9.3; Ni,
8.0; S, 8.3; Cl, 4.8%.
2. Experimental
2.1. Materials
Dipentylamine (97%), 1-benzylpiperazine (98%), 1,4,8,
11-tetraazacyclodecane (cyclam), nitromethane and
K[PF6] were supplied by FLUKA Co. 1,10-Phenanthroline
(phen), 2,20-bipyridine (bpy), LiClO4 Æ 3H2O and dibenzyl-
amine (97%) were acquired from SIGMA ALDRICH Co.
and N-benzylamine (97%) from LANCASTER Co. The
remaining reagents were obtained from LACHEMA Co.,
all of p.a. purity.
2.2.4. [Ni(Bzppzdtc)2]
The complex was prepared by a slightly modified proce-
dure described previously [18]. 1-Benzylpiperazine (8.7 mL,
50 mmol) was added drop-wise to a solution of CS2 (3 mL,
50 mmol) in ethanol (96%, 25 mL) with stirring. A white
precipitate, which formed during the above reaction, was
dissolved by adding a solution of NaOH (1.9 g, 50 mmol)
in water (10 mL). The resulting solution was filtered and
a warm solution of NiCl2 Æ 6H2O (5.9 g, 25 mmol) in water
(50 mL) was added with stirring to the filtrate. Subsequent
steps are identical to those described for the preparation of
[Ni(BzMetdtc)2] (see Section 2.2.1). Yield: 81%. Anal. Calc.
for C24H30N4NiS4: C, 51.3; H, 5.4; N, 10.0; Ni, 10.5; S,
22.8. Found: C, 51.0; H, 5.1; N, 9.8; Ni, 10.6; S, 22.5%.
2.2. Syntheses
2.2.1. [Ni(BzMetdtc)2]
The complex was prepared by a slightly modified proce-
dure described previously [18]. N-Benzylmethylamine
(64 mL, 50 mmol) was added drop-wise into a solution of
CS2 (3 mL, 50 mmol) in ethanol (96%, 25 mL) with stir-
ring. The reaction mixture was left to stand at room
temperature for a short time period. Then, a warm solution
of NiCl2 Æ 6H2O (5.9 g, 25 mmol) in distilled water (50 mL)
was added. After the solution addition, the light green pre-
cipitate of [Ni(BzMetdtc)2] appeared. It was filtered off,
washed with warm water (until negative reaction on Clꢀ
ions) and dried at 40 ꢁC under an infrared lamp. Yield:
72%. Anal. Calc. for C18H20N2NiS4: C, 47.9; H, 4.5; N,
6.2; Ni, 13.0; S, 28.4. Found: C, 48.0; H, 4.4; N, 5.9; Ni,
12.8; S, 28.7%.
2.2.5. [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3)
A mixture of finely powdered [Ni(Bzppzdtc)2] (0.39 g,
2 mmol), phen (0.39 g, 2 mmol), NiCl2 Æ 6H2O (0.11 g,
0.5 mmol) and LiClO4 Æ 3H2O (0.16 g, 1 mmol) were sus-
pended in an ethanol/chloroform mixture (15/15 mL).

Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
413
The reaction mixture was stirred under reflux until all
components dissolved and the colour of the solution turned
to dark red (ca. 4 h). Then, the solution was filtered with
activated carbon and the filtrate was left to stand at room
temperature for 7 days. During this period, a green sub-
stance appeared and it was separated by filtration and dis-
carded. Subsequently, brown crystals suitable for X-ray
analysis formed in the mother liquor after several days.
They were filtered off, washed with hexane and dried under
an infrared lamp at 40 ꢁC. Yield: 56%. Anal. Calc. for
C37H32N6NiS2Cl4O4 (3): C, 50.0; H, 3.6; N, 9.4; Ni, 6.6;
S, 7.2; Cl, 15.9. Found: C, 50.4; H, 3.3; N, 9.5; Ni, 6.3;
S, 7.0; Cl, 15.6%.
and (8), respectively, which were washed with methanol
or hexane and dried under an infrared lamp at 40 ꢁC.
Yields: 62% (7) and 58% (8). Anal. Calc. for C28H44N4NiS4
(7): C, 51.6; H, 6.8; N, 12.9; Ni, 9.0; S, 19.7. Found: C,
51.1; H, 7.2; N, 12.8; Ni, 8.9; S, 19.5%. Anal. Calc. for
C40H52N6NiS4 (8): C, 59.8; H, 6.5; N, 10.4; Ni, 7.3; S,
16.0. Found: C, 59.3; H, 6.9; N, 10.5; Ni, 7.8; S, 15.7%.
2.2.9. [Ni(Bz2dtc)2(phen)] (9)
Phen (0.20 g, 1 mmol) and LiClO4 Æ 3H2O (0.16 g,
1 mmol) were added to a suspension of finely powdered
[Ni(Bz2dtc)2] (0.60 g, 1 mmol) in methanol (15 mL) with
stirring and the mixture was refluxed for 30 min. Then, a
yellow substance formed. It was filtered off, washed with
methanol, and dried under an infrared lamp at 40 ꢁC.
Yield: 85%. Anal. Calc. for C42H36N4NiS4 (9): C, 64.4;
H, 4.6; N, 7.1; Ni, 7.5; S, 16.4. Found: C, 64.1; H, 4.2;
N, 7.4; Ni, 7.3; S, 16.1%.
2.2.6. [Ni(Bzppzdtc)(phen)2](SCN) (4)
Finely powdered [Ni(Bzppzdtc)2] (0.28 g, 0.5 mmol)
together with phen (0.39 g, 2 mmol) and Ni(SCN)2 Æ 2H2O
(0.11 g, 0.5 mmol) were suspended in an ethanol/chloro-
form mixture (15/15 mL) and stirred under reflux for 4 h.
After filtration of the reaction mixture with activated car-
bon, a light brown precipitate formed in the mother liquor
in the course of a few days. The product was filtered off,
washed with hexane and dried under an infrared lamp at
40 ꢁC. Yield: 57%. Anal. Calc. for C37H31N7NiS3 (4): C,
61.0; H, 4.3; N, 13.5; Ni, 8.1; S, 13.2. Found: C, 60.4; H,
4.2; N, 13.2; Ni, 7.9; S, 13.5%.
2.3. Physical measurements
The nickel content was determined by chelatometric
titration using murexide as an indicator [19]. Chlorine con-
tent was determined by the Scho¨niger method [20]. CHNS
analyses were performed on an EA 1108 analyzer (Fisons
Instruments) instrument with satisfactory results for all
the prepared complexes. Room temperature magnetic sus-
ceptibilities were measured by Faraday method on a labo-
ratory designed instrument equipped with a Sartorius 4434
MP-8 microbalance, using Co[Hg(NCS)4] as a calibrant.
The correction for diamagnetism was performed using Pas-
cal constants. Conductivities were measured with an LF
330/SET conductivity meter (WTW GmbH) at 25 ꢁC. Dif-
fuse-reflectance (45000–9090 cmꢀ1) and DMFA solution
(30000–9090 cmꢀ1) electronic spectra were carried out on
a Perkin–Elmer Lambda35 UV/Vis spectrometer. Nujol
technique. IR spectra (4000–450 cmꢀ1) were recorded on
a Perkin–Elmer Spectrum One FT-IR spectrometer using
the KBr technique. TG/DTA analyses were performed on
an Exstar TG/DTA 6200 (Seiko Instruments, Inc.) with
the heating rate of 2.5 ꢁC minꢀ1, sample weight of 7–
11 mg, and temperature range of 20–1050 ꢁC.
The study the catalytic influence of the complexes 2, 3, 6,
and 7 on graphite was performed on a Netzsch STA 449C
device with an a-Al2O3 crucible without a standard, heat-
ing rate of 10 ꢁC minꢀ1, a sample weight of 4.4–5.1 mg,
and in a dynamic atmosphere (air, 100 cm3 minꢀ1). Sam-
ples for the study were prepared by the mixing of graphite
(0.6 g, diameter of particles less than 0.1 mm, ash residue
max. 0.2%, mass drying loss max. 0.2%) with an acetone
solution (2 mL) of the appropriate complex (2, 3, 6 and
7; [Ni] = 2.5 mM). All samples were homogenized by
means of stirring and drying at room temperature for
24 h. Each experimental result is represented as an arithme-
tic mean of three independent experiments. The kinetic
parameters were calculated by a direct non-linear regres-
sion method [21].
2.2.7. [Ni(Pe2dtc)(cyclam)]ClO4 (6)
A suspension of finely powdered [Ni(Pe2dtc)2] (0.52 g,
1 mmol) in chloroform (5 mL) was mixed while stirring
with 1,4,8,11-tetraazacyclodecane (0.2 g, 1 mmol) in 96%
ethanol (5 mL) and LiClO4 Æ 3H2O (0.16 g, 1 mmol) in
96% ethanol (3 mL). The reaction mixture was stirred
under reflux for 10 h. The resulting violet solution was
filtered with activated carbon and left to stand at room
temperature. After one week, a viscous product was
obtained which was extracted with diethyl ether. After
three days, the viscous product was formed again from
which a powdered substance was isolated by means of
diethyl ether. It was filtered off and dried under an infrared
lamp at 40 ꢁC. Yield: 46%. Anal. Calc. for C21H46N5Ni-
S2ClO4 (6): C, 42.7; H, 7.8; N, 11.8; Ni, 9.9; S, 10.8; Cl,
6.0. Found: C, 42.5; H, 7.5; N, 11.6; Ni, 9.8; S, 10.5; Cl,
5.5%.
2.2.8. [Ni(BzMetdtc)2(cyclam)] (7) and
[Ni(Bz2dtc)2(cyclam)] (8)
These compounds were obtained by the reaction of
finely powdered [Ni(Bz2dtc)2] (0.6 g, 1 mmol) or [Ni(Bz-
Metdtc)2] (0.45 g, 1 mmol) in chloroform (5 mL) with
1,4,8,11-tetraazacyclodecane (cyclam) (0.2 g, 1 mmol) in
96% ethanol (10 mL). The mixture was stirred under reflux
for 10 h and the resulting violet solution was filtered. Dur-
ing a few days, violet crystals, or a violet powder substance
appeared. The product was recrystallized from chloroform
by addition of methanol or hexane. The violet powder sub-
stance and violet crystals were isolated in the case of (7),

414
Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
Table 1
Crystal data and structure refinement for [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3) and [Ni(Bz2dtc)2(cyclam)] (8)
3
8
Empirical formula
Formula weight
Temperature (K)
C37H32Cl4N6NiO4S2
889.32
105(2)
0.71073
C40H46N6NiS4
797.78
105(2)
0.71073
˚
Wavelength (A)
Crystal system, space group
P21/c
12.799(3)
16.864(3)
P21/c
9.2729(3)
19.7667(5)
˚
a (A)
˚
b (A)
˚
c (A)
17.691(5)
10.8490(4)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
92.18(2)
90
3815.7(17)
4, 1.548
0.948
1824
90
97.151(3)
90
1973.09(117)
2, 1.343
0.740
840
3
˚
Volume (A )
Z, calculated density (g cmꢀ3
)
)
Absorption coefficient (mmꢀ1
F(000)
Crystal size
h range for data collection (ꢁ)
Index ranges
Reflections collected/unique
Refinement method on F2
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
0.40 · 0.35 · 0.30 mm
2.68–25.00
ꢀ15 6 h 6 15, ꢀ20 6 k 6 20, ꢀ15 6 l 6 21
33494/6713 (Rint = 0.0282)
full-matrix least-squares
0.983
R1 = 0.0424, wR2 = 0.1197
R1 = 0.0562, wR2 = 0.1289
0.727 and ꢀ0.979
0.40 · 0.40 · 0.30 mm
2.80–25.00
ꢀ11 6 h 6 10, ꢀ23 6 k 6 13, ꢀ12 6 l 6 12
10042/3462 (Rint = 0.0201)
full-matrix least-squares
1.020
R1 = 0.0594, wR2 = 0.1265
R1 = 0.0762, wR2 = 0.1329
0.820 and ꢀ0.552
ꢀ3
˚
Largest difference in peak and hole (e A
)
2.4. X-ray structures
to the high degree of disorder, a relatively high number of
restrains (ꢂ91) have been applied during the structural
refinement of 8, and moreover, a few H-atoms were not
included into the refinement. H-atoms were positioned
theoretically and refined using the riding model with the
X-ray data collections for 3 and 8 were performed on an
Oxford Diffraction Xcaliburꢂ2 equipped with a Sapphire2
CCD detector using Mo Ka radiation at 105 K. The
CRYSALIS program package (version 1.171.32.5, Oxford
Diffraction) was used for data collection and reduction.
The molecular structure of 3 was solved by direct methods
[SHELXS-97] [22] and all non-hydrogen atoms were refined
anisotropically on F2 using full-matrix least-squares proce-
dure [SHELXL-97] [23] with weight: w = 1/[r2(Fo)2 +
˚
C–H distances of 0.95 and 0.99 A, and N–H distance of
˚
0.93 A. Crystal data and structure refinements for both
the structures are given in Table 1.
3. Results and discussion
(0.08P)2 + 5.00P], where P = (Fo2 + 2Fc )/3. All H-atoms
3.1. General characterization
2
of 3 were found in differential maps of electron density
and their parameters were refined using the riding model
with the C–H distance of 0.95, 0.99, and 1.00 A, respec-
Colours, magnetic moment, molar conductivity and
spectral data of all the prepared complexes 1–9 are summa-
rized in Table 2. All complexes are paramagnetic with val-
ues of effective magnetic moments ranging from 3.02 to
3.41leff/lB. These values indicate the presence of two
unpaired electrons and show on octahedral geometry in
the vicinity of the nickel atom [25]. The octahedral geome-
try can also be supported by the d–d transition bands
revealed both in electronic diffuse-reflectance and DMFA
solution spectra at 10280–11720, 16180–19960 and
21929–26230 cmꢀ1 (see Table 3). They may be assigned
˚
tively, and with Uiso(H) = 1.2Ueq(C). Additional calcula-
tions were performed using the DIAMOND program [24].
The molecular structure of 8 was solved by direct methods
[SHELXS-97] and all non-hydrogen atoms were refined
anisotropically on F2 using full-matrix least-squares proce-
dure [SHELXL-97] with weight: w = 1/[r2(Fo)2 + (0.03P)2 +
5.00P]. The structure of 8 consists of a centrosymmetric
Ni1/2(Bz2dtc)(cyclam)1/2 moiety which is connected with
its second part by means of an inversion centre [symmetry
a
3
3
3
3
3
code: ꢀx, ꢀy + 1, ꢀz + 1] lying in the middle of Ni1ꢁ ꢁ ꢁ
to the A2g ! T2g (m1), A2g ! T1g (F) (m2), and A2g !
Ni1a distance. The separation of Ni1ꢁ ꢁ ꢁNi1a is
3T1g(P) (m3) transitions, respectively [26]. The maxima
above 30000 cmꢀ1 are probably caused by charge-transfer
transitions. An ionic nature of complexes 1–6 may be sup-
ported by their molar conductivity data. It has been found
that the complexes behave as 1:1 electrolytes in acetone or
DMFA solution [27]. Their molar conductivity values are
˚
2.3962(16) A. The N2–N4 and C20 atoms of the moiety
belonging to cyclam are disordered over two positions with
the occupancy of 36% (for N2 and N4), 64% (for N3), 32%
(for C20) and 33% (for C20b), and 14% (for N2a and N4a),
36% (for N3a), 15% (for C20a) and 20% (for C20c). Owing

Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
415
Table 2
Colour, molar conductivity, magnetic moment, spectral and thermal data for the complexes
Colour
kM (S cm2 molꢀ1
)
leff/lB
IR (cmꢀ1
)
TAa (ꢁC)
m (CAS)
m (CAN)
c
c
c
1
2
3
4
5
6
7
8
9
yellow
148.6b
146.2b
132.8b
147.2d
135.5b
111.1b
3.4b
3.04
3.21
3.16
3.41
3.02
3.07
3.07
3.12
3.20
994m
992m
996m
996s
992m
995m
996m
983vs
999vs
1515w
1515s
1514m
1515vs
1514m
1493s
1522m
1493s
1513m
m3(ClO4ꢀ): 1089vs; m4(ClO4ꢀ): 623s
m3(ClO4ꢀ): 1096vs; m4(ClO4ꢀ): 623vs
m3(ClO4ꢀ): 1095vs; m4(ClO4ꢀ): 622s
mas(C„N): 2083vs
dark red
dark brown
light brown
yellow
light violet
light violet
violet
193
c
m3(ClO4ꢀ): 1084m; m4(ClO4ꢀ): 626m
m3(ClO4ꢀ): 1087vs; m4(ClO4ꢀ): 624vs
c
134
163
190
25.2d
grey
10.0d
(1) [Ni(BzMetdtc)(phen)2]ClO4; (2) [Ni(Pe2dtc)(phen)2]ClO4; (3) [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3; (4) [Ni(Bzppzdtc)(phen)2](SCN); (5) [Ni(Bz-
Metdtc)(bpy)2]ClO4 Æ 2H2O; (6) [Ni(Pe2dtc)(cyclam)]ClO4; (7) [Ni(BzMetdtc)2(cyclam)]; (8) [Ni(Bz2dtc)2(cyclam)]; (9) [Ni(Bz2dtc)2(phen)].
a
The beginning of thermal decomposition.
Measured in acetone.
Did not studied owing to the explosiveness.
Measured in DMFA solution.
b
c
d
Table 3
in the interval of 111.1–148.6 S cm2 molꢀ1. On the other
UV/Vis spectral data for the complexes
hand, the values obtained for complexes 7–9 clearly show
on the fact that they are non-electrolytes (see Table 2).
Characteristic IR bands and their assignment are given in
Table 2.
Diffuse-reflectance
UV/Visa Solutionb
e (dm3 cmꢀ1 molꢀ1
)
1
2
3
4
5
6
7
8
9
11720
26230
31100
10834
11363
17391
25125
14
27
87
675
3.2. IR spectral studies
11810
19620
10294
11194
19792
25252
14
28
17
512
For all complexes 1–9, the bands belonging to m(Cꢁ ꢁ ꢁS)
and m(Cꢁ ꢁ ꢁN) vibrations were observed at 983–999 cmꢀ1
,
and 1493–1542 cmꢀ1, respectively [28,29]. These values
clearly characterize the dithiocarbamate moiety. Owing
to the fact that intensive bands pertaining to m(Cꢁ ꢁ ꢁS)
are not splitted into two components, we can conclude
that dithiocarbamate anion is coordinated to nickel in a
11540
19810
10718
11376
19960
25316
17
24
131
532
10680
17790
10256
11641
16181
20040
8
10
31
96
ꢀ
bidentate fashion. The presence of ClO4 in complexes
1–3, 5 and 6, as well as its ionic nature, can be supported
by bands at 1084–1096 cmꢀ1 (m3) and 622–626 cmꢀ1(m4)
[30]. The peak recorded at 2083 cmꢀ1 in the spectrum of
4 may be assigned to an asymmetric stretching vibration
of an ionic bonded NCSꢀ anion [31]. The conclusions fol-
lowing from the interpretation of IR spectral data of
[Ni(BzMetdtc)2(cyclam)] (7) and [Ni(Bz2dtc)2(cyclam)] (8)
are not unambiguous and at this point, and unfortu-
nately, we cannot make decision if the bidentate manner
of coordination of dithiocarbamate would be possible in
the case of the discussed complexes. Generally, we may
assume the tetradentate coordination of cyclam and the
bidentate coordination of each of two dithiocarbamate
ligands, and thus, to accept the non-ionic nature of the
complexes as determined by conductivity measurements.
It would point out that the coordination number for
nickel would be eight, and evidently, this is not possible
in the case of the ligand’s combination used. However,
the manner of ligand coordinations in 7 and 8 has been
resolved by means of single crystal X-ray analysis and will
be explained and discussed in greater details in the
Section 3.3.
11690
167·80
24050
30030
10638
16393
20000
24398
12
36
96
156
11240
17790
31480
10752
11350
17921
23201
47
55
73
75
10530
16180
22440
30100
10791
11287
18116
22676
35
44
67
77
11320
18110
10799
11363
18018
24937
16
17
28
72
10280
16280
20390
10706
11389
20040
21929
15
24
80
86
Absorption maxima in cmꢀ1
.
a
Measured in DMFA solutions [cM = 10ꢀ3 mol dmꢀ3 for 1–7; cM = 10ꢀ2 mol
b
dmꢀ3 for 8–9].

416
Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
3.3. X-ray structures of
[Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3) and
[Ni(Bz2dtc)2(cyclam)] (8)
plexes (the mean value in delocalizꢀed C–S bonds is
˚
1.713 A) [6]. The ionic nature of ClO4 in 3 can be seen
˚
from the Niꢁ ꢁ ꢁCl separation which is 6.5912(13) A.
The structure of 8 consists of a centrosymmetric
Ni1/2(Bz2dtc)(cyclam)1/2 moiety which is connected with
its second part by means of inversion centre [symmetry
code: a ꢀx, ꢀy + 1, ꢀz + 1]. Thus, the Ni1 atom and some
atoms of cyclam adopt non-unit occupancy factors. The
crystallographically independent part of the complex mol-
ecule is connected with its second centrosymmetric part
through partially disordered cyclam ligand. The separation
The molecular structure of complex 3 and 8 is depicted
in Figs. 1 and 2, respectively. Selected bond lengths and
angles are given in Table 4. The molecular structure of
[Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3) consists of the [Ni-
(Bzppzdtc)(phen)2]+ cation, perchlorate anion, and CHCl3
as a solvent molecule. The nickel(II) ion is six-coordinated
by four nitrogen atoms from two phen ligands and two sul-
phur atoms from 4-benzylpiperazinedithiocarbamate anion
in a distorted octahedral geometry. The [Ni(Bzppzdtc)-
(phen)2]+ cation contains three different rings, i.e. the phen
ligand containing N1 and N2 atoms (ring 1), phen ligand
containing N3 and N4 atoms (ring 2) and a part of dithio-
carbamate moiety together with the nickel atom involving
a NiS2C moiety (ring 3). All three rings are nearly planar
˚
of Ni1ꢁ ꢁ ꢁNi1a is 2.3962(16) A. The presence of the above-
mentioned symmetry operation together with the disorder
causes that each of the two parts of the nickel atom is six
coordinated by four N atoms from cyclam and two S
atoms from a bidentate coordinated dithiocarbamate
ligand. Moreover, it also explains why may be coordinated
the dithiocarbamate ligand to nickel via two S atoms. It
also clearly supports conclusions following from IR data.
Similarly as in 3, a significant delocalization of p-electron
density over the S2CN moiety in 8, as typical for a biden-
tate coordination of any dithiocarbamate anion to a tran-
sition metal, may be evident from the C–N and C–S
bond length values (see Table 4).
˚
with maximal deviation being 0.099(5) A for C(8),
˚
˚
0.054(4) A for C(20) and 0.074(4) A for C(25) in rings 1–
3, respectively [24]. The dihedral angle between rings 1
and 2, 1 and 3, and 2 and 3 are equal to 81.88(4)ꢁ,
88.65(4)ꢁ, and 86.02(4)ꢁ, respectively. The delocalization
of p-electron density over the S2CN moiety, as typical for
a bidentate coordination of any dithiocarbamate anion to
a transition metal, may be evident from the C–N and C–
S bond length values (see Table 4). For comparison, mean
values for C–N, C@S and C–S bonds, as found in Cam-
bridge Structural Database (CSD Version 5.28), are
In conclusion of this section, it is necessary to emphasize
that the discussed structures represent the first examples of
structurally characterized octahedral Ni-dithiocarbamate
complexes bearing a combination of the ligands used.
˚
˚
1.331 A (valid for S2CNR2 moiety), 1.661 A (valid for
3.4. TG and DTA studies
˚
S2CNR2 moiety), and 1.753 A (valid for R–S–R), respec-
tively [6]. On the other hand, the C–S bond lengths in 3
and 8 are comparable to those as determined for bidentate
coordinated dithiocarbamate moieties in case of Ni-com-
Thermal stability studies were performed for complexes
4, 7, 8 and 9. The remaining compounds, i.e. those contain-
ing perchlorate anions, were not studied for safety reasons.
Fig. 1. The molecular structure of [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3) with the atom labelling scheme. Thermal ellipsoids are drawn at the 40%
probability level. H-atoms and CHCl3 molecule have been omitted for clarity.

Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
417
Fig. 2. The molecular structure of [Ni(Bz2dtc)2(cyclam)] (8) with the atom labelling scheme, showing partially disordered cyclam ligand. Thermal
ellipsoids are drawn at the 40% probability level. H-atoms and some of disordered cyclam atoms have been omitted for clarity.
Table 4
˚
Selected bond lengths (A) and angles (ꢁ) for [Ni(Bzppzdtc)(phen)2]ClO4 Æ CHCl3 (3) and [Ni(Bz2dtc)2(cyclam)] (8)
3
8
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(4)
Ni(1)–S(1)
Ni(1)–S(2)
S(1)–C(25)
S(2)–C(25)
N(5)–C(25)
2.096(3)
2.099(3)
2.072(3)
2.099(3)
2.4020(11)
2.4438(9)
1.719(3)
1.713(4)
1.334(5)
N(1)–Ni(1)–N(2)
N(3)–Ni(1)–N(4)
S(1)–Ni(1)–S(2)
N(3)–Ni(1)–N(2)
N(1)–Ni(1)–S(1)
N(4)–Ni(1)–S(2)
C(25)–S(1)–Ni(1)
C(25)–S(2)–Ni(1)
S(1)–C(25)–S(2)
79.29(12)
79.53(12)
73.85(3)
168.69(10)
170.75(7)
165.63(7)
85.53(11)
84.34(11)
116.08(18)
Ni(1)–N(2)
Ni(1)–N(2a)
Ni(1)–N(3)
Ni(1)–N(3a)
Ni(1)–N(4)
Ni(1)–N(4a)
Ni(1)–S(1)
Ni(1)–S(2)
S(1)–C(1)
2.133(9)
2.17(3)
2.022(12)
1.99(2)
2.085(9)
2.13(2)
2.5958(15)
2.5898(13)
1.715(4)
1.703(4)
1.344(4)
N(3)–Ni(1)–N(4)
N(3)–Ni(1)–N(2)
N(4)–Ni(1)–N(2)
S(2)–Ni(1)–S(1)
S(2)–C(1)–S(1)
C(1)–S(1)–Ni(1)
C(1)–S(2)–Ni(1)
89.3(5)
84.2(5)
170.5(3)
69.22(4)
119.0(2)
85.66(13)
86.08(13)
S(2)–C(1)
N(1)–C(1)
Generally, we can note that the studied complexes are not
comparatively thermally stable. They start to decompose
within a relatively broad temperature interval of 134–
193 ꢁC. In the case of complexes 4, 7 and 8, the decays pro-
ceed without formation of thermally stable intermediates in
several steps and are not finished even at 1050 ꢁC. The
decompositions are accompanied by several exo-effects on
DTA curves in the case of the discussed complexes. The
dominant exo-effects were observed at ca. 480 ꢁC and it
may be probably connected with the decomposition of
the organic part of the complex. As for the thermal decay
of 9, the situation is a little bit different. That is why we will
discuss it in greater detail. The complex 9 starts to decom-
pose at 190 ꢁC and the beginning of the decay is accompa-
nied by significant decrease in the sample weight (ca. 56%).
At the first stage of the decomposition, three small endo-
effects can be seen on the DTA curve with the minimum
at 236, 267, and 350 ꢁC, respectively (see Fig. 3). The
endo-effect with the maximum at 236 ꢁC may be related
to melting of the sample which was determined using melt-
ing point apparatus to be 234 ꢁC. Next thermal decay pro-
ceeds in two waves and is finished at 705 ꢁC. A sharp exo-
effect with the maximum at 476 ꢁC is clearly seen on the
DTA curve, and is probably connected with the burning
of the organic part of the molecule. Then, a plateau exists
on the TG curve between 706 and 1050 ꢁC. It has been
found that the end-product of the thermal degradation is
NiO (Dm found/calcd., 89.2/91.7%). The product was iden-
tified using the Bede ZDS program package [32] and PDF-
2 database [33] as NiO (PDF-2 card number: 47–1049).
3.5. The catalytic study
For representative complexes 2, 3, 6 and 7, their influence
on graphite oxidation was studied. In quest to evaluate
obtained results objectively, we also measured the oxidation
of pure graphite (gr) and considered an impact of pure ace-
tone (sample 0), as a solvent used for the preparation of the

418
Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
Table 5
Characteristic temperatures (ꢁC) of graphite, acetone and their mixtures
with complexes
Sample
Tp
Tm
Tk
Tk ꢀ Tp
Pure graphite (gr)
Pure acetone (0)
2
3
6
7
775
763
704
706
705
702
834
822
806
804
807
807
862
854
848
846
848
849
87
91
144
140
143
147
Tp – the beginning of oxidation; Tm – oxidation rate maximum; Tk – the
end of oxidation.
Table 6
Kinetic parameters of oxidation of graphite, acetone and their mixtures
with complexes
Fig. 3. TG and DTA curves for [Ni(Bz2dtc)2(phen)] (9).
Sample
Step
n
A (sꢀ1
)
E (kJ molꢀ1
)
w (%)
Pure graphite (gr)
Pure acetone (0)
0.7
0.7
9.50 · 108
241
222
samples containing the complexes, on the course of the oxi-
dation. A comparison of the oxidation courses of the above-
mentioned samples is depicted in the form of their DTG
curves in Fig. 4. Characteristic temperatures and kinetic
parameters obtained from TG curves are summarized in
Tables 5 and 6, respectively. It has been found that acetone
application has no significant impact on the graphite oxida-
tion. However, its presence causes only small decrease in
temperature of the oxidation (ca. 10 ꢁC) together with the
decreasing of the activation energy of the process. The pres-
ence of the complexes even in applied trace amount (Ni con-
tent is about 100 mol ppm) has significant impact on the
course of the graphite oxidation, however, this effect is prac-
1.47 · 108
2
3
6
7
I
II
1.0
1.3
5.36 · 105
1.17 · 1017
160
400
53.66
46.34
I
II
0.9
1.1
1.24 · 105
150
341
58.30
41.70
1.35 · 1014
I
II
1.0
1.4
6.00 · 105
3.92 · 1020
162
474
60.91
39.09
I
II
1.0
1.2
2.43 · 105
155
412
63.13
36.87
3.23 · 1017
n – reaction order; A – frequency factor, E – activation energy, w – mass of
sample oxidized.
tically independent on the quality of the admixture used, i.e.
on the complexes themselves. In the presence of the com-
plexes, the oxidation of graphite starts about 60 ꢁC lower
as compared to the sample containing graphite and acetone
but the temperature relating to the termination of graphite
oxidation is not influenced much. It follows that the width
of the temperature interval in which the graphite oxidation
with the samples proceeds is about 50 ꢁC greater as com-
pared to pure graphite. It can be seen from shapes of
DTG curves that the presence of complexes causes bifurcat-
ing of the formerly simple DTG peak, thus graphite
enriched by the complexes is oxidized in two steps in com-
parison of pure graphite.
The calculated values of activation energies (E) and fre-
quency factors (A) show that two observed oxidative steps
of the enriched graphite differ significantly. A bigger por-
tion of graphite is oxidized in the first step with activation
energy values of 150–160 kJ molꢀ1 and frequency factors in
the order of 105–106 sꢀ1. Significantly higher values of both
parameters were determined for the second step. The reac-
tion order was determined to be slightly higher for both
steps (n = 1.0–1.4; see Table 6) as compared to free graph-
ite (n = 0.7). It shows the fact that the kinetics of pure
graphite is determined by its contracting volume (n = 2/3
corresponds to phase boundary controlled reaction, i.e.
mechanism R3), however, the kinetics of oxidation of
Fig. 4. DTG curves of graphite samples containing complexes 2, 3, 6 and,
their comparison with DTG curves for pure graphite (gr) and pure acetone
(0).

Z. Tra´vnı´cˇek et al. / Polyhedron 27 (2008) 411–419
419
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Acknowledgements
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The financial support of this work by The Ministry of
Education, Youth and Sports of the Czech Republic
(a grant no. MSM6198959218) is gratefully acknowledged.
´
Authors also wish to thank to Mrs. Regina Mencelova
for help with the preparation of some complexes, Dr. Zde-
ˇ
[15] R. Vicente, A. Escuer, J. Ribas, A. Dei, X. Solans, T. Calvet,
Polyhedron 9 (1990) 1729.
´ˇ
neˇk Sindelar for magnetic susceptibility measurements
´ˇ
´
´ˇ
[16] R. Pastorek, J. Kamenıcek, B. Cvek, V. Slovak, M. Pavlıcek, J.
ˇ
and Mr. Pavel Starha for performing of TG/DTA
Coord. Chem. 59 (2006) 911.
measurements.
´ˇ
´
´
´ˇ
[17] R. Pastorek, J. Kamenıcek, H. Vrbova, V. Slovak, M. Pavlıcek, J.
Coord. Chem. 59 (2006) 437.
Appendix A. Supplementary material
ˇ
ˇ
´
´ˇ
´ˇ
´ˇ
[18] R. Pastorek, J. Kamenıcek, B. Cvek, M. Pavlıcek, Z. Sindelar, Z. Zak,
J. Coord. Chem. 56 (2003) 1123.
´
[19] R. Prˇibil, Komplexometricke titrace, SNTL, Praha, 1955, p. 22.
CCDC 625271 and 652556 contain the supplementary
crystallographic data for complexes 3 and 8, respectively.
These data can 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; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
ciated with this article can be found, in the online version,
at doi:10.1016/j.poly.2007.09.024.
ˇ
´
´
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