Planar Ni(II) 1,2-dithiolenes involving bidentate P-donor ligands

Article abstract of DOI:10.1016/j.poly.2009.07.067

A series of planar Ni(II) dithiolenes derived of maleonitriledithiol (mnt), benzene-1,2-dithiol (bdt) and toluene-3,4-dithiol (tdt) with bidentate P,P-ligands (dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane, dppb = 1,4-b

Full text of DOI:10.1016/j.poly.2009.07.067

Polyhedron 28 (2009) 3565–3569
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Planar Ni(II) 1,2-dithiolenes involving bidentate P-donor ligands
a
a,
d
Peter Herich , Jirí Kamenícek , Kamil Kuca b,c, Miroslav Pohanka b,c, Milan Olšovsky
*
ˇ
ˇ
ˇ
´
a
ˇ ˇ
Department of Inorganic Chemistry, Palacky´ University, Krízkovského 10, CZ-771 47 Olomouc, Czech Republic
Center of Advanced Studies, Faculty of Military Health Sciences, University of Defence, Trebešská 1575, CZ-500 01, Hradec Králové, Czech Republic
b
c
ˇ
ˇ
Department of Toxicology, Faculty of Military Health Sciences, University of Defence, Trebešská 1575, CZ-500 01, Hradec Králové, Czech Republic
d Department of Chemistry and Technology of Polymers, Faculty of Industrial Technologies, TnUAD, Ivana Krasku 491/30, SK-020 01 Púchov, Slovak Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of planar Ni(II) dithiolenes derived of maleonitriledithiol (mnt), benzene-1,2-dithiol (bdt) and
toluene-3,4-dithiol (tdt) with bidentate P,P-ligands (dppe = 1,2-bis(diphenylphosphino)ethane, dppp =
1,3-bis(diphenylphosphino)propane, dppb = 1,4-bis(diphenylphosphino)butane, dpppn = 1,5-bis(diphen-
ylphosphino)pentane) of the [Ni(P,P)(dithiol)] type have been synthesized. The compounds have been
characterized by elemental analysis, IR and electronic spectroscopies, magnetochemical, conductivity
measurements and thermal analysis. Single crystal X-ray analysis of [Ni(dpppn)(mnt)] confirmed a planar
geometry of NiP2S2 chromophore. Possible practical applications such as use of these compounds for
vulcanization accelerators and their anticholinesterase activity were evaluated.
Received 18 May 2009
Accepted 12 July 2009
Available online 27 August 2009
Keywords:
Nickel(II)
Dithiolenes
X-ray structure
Vulcanization agents
Cholinesterase
Inhibitor
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
The aim of this work was the synthesis and physico-chemical
study of integrated series of selected Ni(II) dithiolene complexes
A square-planar coordination polyhedron is very common for
nickel dithiolenes with NiS4 chromophore containing two S,S-
ligands (bdt, tdt) and a number of complexes of the R[Ni(S,S)2]
and R2[Ni(S,S)2] types (R = NR4+, PR4+) have been reported [1–5].
The situation is different for complexes, where one S,S-ligand is
replaced by a N,N- or P,P-ligand. In our previous work [6], the
dithiolate complexes with the coordination number four involving
N,N-ligands were studied and many nickel complexes with bdt,
phen and nphen ligands (nphen = 5-nitro-1,10-phenanthroline)
were reported as well [7–9]. Whereas a square-planar Ni(II)dithio-
carbamate complexes with monodentate P- and bidentate P,P-li-
gands were extensively studied [10–17], a similar Ni(II)dithiolate
complexes namely with the P,P-ligands were published less
commonly. For instance, authors [18] described the synthesis of
[Ni(dppe)(mnt)], authors [19] the [Ni(dppe)(mnt)]ꢀCH2Cl2, authors
[20] the [Co(dppe)(bdt)] complex, all including X-ray analysis.
Authors [21] published the synthesis of [Ni(dppe)(tdt)] with
X-ray analysis and possibility of a reversible SO2 absorption.
Recently, a number of practical applications were reported, some
of nickel complexes can be used as biologically active model
compounds [22,23]; see also references on possible using as
superconductors, analytical species, polarization filters, pesticides,
vulcanization catalysts and special developers [24–28].
with bidentate S,S-ligands (bdt, tdt and mnt) combined with
bidentate P,P-ligands (dppe, dppp, dppb, dpppn), including X-ray
analysis of a selected sample. Moreover, potential practical appli-
cations (using of samples as vulcanization accelerators and as cho-
linesterase inhibitors) are investigated.
2. Experimental
2.1. Materials and methods
For syntheses, the following reagents were used:
ꢁ 1,2-Bis(diphenylphosphino)ethane P98%,
ꢁ
1,3-Bis(diphenylphosphino)propane P97%, 1,4-Bis(diphenyl-
phosphino)butane P98%, 1,5-Bis(diphenylphosphino)pentane
P95%,
ꢁ Dimercaptomaleonitrile disodium salt hydrate P95%, toluene-
3,4-dithiol P97%,
ꢁ Benzene-1,2-dithiol P95% (SIGMA–ALDRICH).
All solvents were products of LACHEMA Brno. For evaluation of
anticholinesterase activity, chemicals of analytical grade from SIG-
MA–ALDRICH were used.
The nickel content was determined by chelatometric titration
using murexide as indicator [29]. CHNS analyses were performed
on a Fisons EA 1108 instrument; satisfactory analyses for all above
* Corresponding author. Tel.: +420 585634353.
E-mail address: jiri.kamenicek@upol.cz (J. Kamenícek).
ˇ
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.067

3566
P. Herich et al. / Polyhedron 28 (2009) 3565–3569
complexes were obtained (Table 1). IR spectra (4000–450 cmꢂ1
)
process. In the second step, the accelerator of TBBS type (N-tert-bu-
tyl-2-benzothiazolesulfenamide) was replaced by the selected sam-
ples (other vulcanizing system dopes were unchanged). Preparation
of the rubber mixture was performed by Plastograf – Brabender de-
vice (Plastograf Duisburg, DE) at 110 °C, during 7 min with a stirring
speed 50 minꢂ1 according [31]. After the preparation, the rubber
mixture was left to stand for 24 h and the appropriate vulcanizing
curves were recorded (Table 7). For this purpose, the Monsanto
100 device at 150 °C was used (recording time 60 min) by the nor-
malized procedure mentioned above. The vulcanization of the rub-
ber compound was implemented in a laboratory press BUZULUK
(Buzuluk Komárov, CZ) at 150 °C under the pressure of 20 MPa.
After vulcanization, the rubber mixtures were left to stand at labo-
ratory temperature for 24 h and the double-sided paddle testing
elements for stress–strain measurements were isolated. Stress–
strain properties were measured with the shredder machine IN-
STRON and the hardness of rubber mixture was measured manually
by the IRHD device by the normalized procedure [31].
were recorded on a Perkin–Elmer Spectrum One FT-IR spectrome-
ter using KBr pellets. Absorption electron spectra (45 000–
9090 cmꢂ1) were carried out on a Perkin–Elmer Lambda 35 UV/
VIS spectrophotometer using N,N-dimethylformamide as solvent.
Conductivities were measured with an LF 330/SET conductivity
meter (WTW GmbH) at 25 °C. Room temperature magnetic
susceptibilities were measured by the Faraday method using
Co[Hg(NCS)4] as a calibrant on a laboratory designed instrument
with a Sartorius 4434 MP-8 microbalance. Thermal analysis was
performed on Exstar 6000 device (Seiko Instruments Inc.).
Anticholinesterase activity measurement: Electrochemical strips
with platinum working (diameter 1 mm), Ag/AgCl reference and
platinum auxiliary electrodes were obtained from BVT (Brno, Czech
Republic). Acetylcholinesterase (AChE) from electric eel (obtained
from Sigma–Aldrich) was immobilized onto the working electrode
as a precipitate with glutaraldehyde and bovine serum albumin
(BSA). Two microliter of mixture consisting of total 0.01 nkat of
AChE, 1 mg BSA and 0.1% glutaraldehyde was injected onto the
working electrode and let to form a layer in a closed chamber.
In order to realize the assay, biosensor was fixed horizontally
and connected with an electrochemical device EmStat (Palmsens,
Houten, The Netherlands). Twenty microliter of 1 mmol acetylthi-
ocholine chloride (ATChCl) in 50 mmol phosphate buffer pH 7.4
2.2. Syntheses
For syntheses of complexes with the bdt, tdt-ligands, the mod-
ified procedure of Darkwa [21] was used: Complexes with the bdt,
tdt-ligands were obtained by mixing the appropriate ligand: tdt
(0.16 g, 1 mmol) or bdt (0.14 g, 1 mmol) in toluene (10 ml) with
triethylamine (0.3 ml). Finally, NiCl2ꢀ6H2O (0.24 g, 1 mmol) in
methanol (10 ml) and the appropriate P,P-ligand – dppe (0.40 g),
dppp (0.41 g), dppb (0.42 g) or dpppn (0.44 g) in toluene (40 ml).
The resulting mixture was stirred under reflux at 50 °C for 1 h.
The resulted powder substance was separated by filtration, washed
with methanol and diethylether and dried at room temperature
(yield 85%).
For syntheses of complexes with mnt, the modified procedure
of Bowmaker [28] was performed: Na2(CN)2C2S2 (0.19 g, 1 mmol),
NiCl2ꢀ6H2O (0.24 g, 1 mmol) and P,P-ligand – dppe (0.40 g), dppp
(0.41 g), dppb (0.42 g) or dpppn (0.44 g) were mixed as solids,
and acetone (40 ml) was added. The resulting solution was stirred
for 1 h. The complexes were precipitated by the slow addition of
water and vigorous stirring. The solid substance was filtered from
the solution, washed with water, ethanol and diethylether and
dried at room temperature (yield 98%).
was spread over the electrodes commonly with another 20 ll of
tested sample in DMSO. The output current was measured after
one minute. The percentage of AChE activity inhibition (I) was
calculated using the following equation:
ꢀ
ꢁ
ii
it
I ¼ 1 ꢂ
ꢃ 100
where ii means the current provided by the biosensor inhibited by
the sample and it by the intact biosensor (20 ll of DMSO solution
only) [30].
Vulcanization activity measurement: As standards, the follow-
ing materials were used: Vuchtalink FMI/G-80 (1.96 dsk, antire-
versible and adhesion agent); Santocure TBBS GRS 2 MM (0.92
dsk, accelerator of vulcanization: N-tert-butyl-2-benzothiazole-
sulfenamide); Sulphur N (5.03 dsk, vulcanizing agent); Duslin
G-80 (0.12 dsk, inhibitor of overvulcanization); Rubber mixture
I.° (190.18 dsk).
S
Crystals of [Ni(dpppn)(mnt)] for X-ray analysis were obtained
in a similar way, using methanol (30 ml). During 24 h, the brown
prismatic crystals precipitated and a single crystal suitable for
X-ray analysis was selected.
S
N
NH
Vulcanization standard Santocure TBBS GRS 2 MM
The efficiency of the samples as vulcanization accelerators for
the side-wall mixtures for car radial tyres was studied. The rubber
mixtures were prepared by the double-stirring procedure. In the
first step, rubber mixture was recovered directly from the industrial
2.3. X-ray crystallography
X-ray data collection for [Ni(dpppn)(mnt)] was performed on an
Oxford Diffraction XcaliburTM2 four circle
j
-axis diffractometer
Table 1
Analytical data.
Compound
M [g molꢂ1
]
Calc./found
Ni (%)
C (%)
H (%)
N (%)
S (%)
I. [Ni(dppe)(mnt)]
II. [Ni(dppp)(mnt)]
III. [Ni(dppb)(mnt)]
IV. [Ni(dpppn)(mnt)]
V. [Ni(dppe)(bdt)]
VI. [Ni(dppp)(bdt)]
VII. [Ni(dppb)(bdt)]
VIII. [Ni(dpppn)(bdt)]
IX. [Ni(dppe)(tdt)]
X. [Ni(dppp)(tdt)]
XI. [Ni(dppb)(tdt)]
XII. [Ni(dpppn)(tdt)]
597.30
611.33
625.36
639.38
597.30
611.37
625.39
639.42
612.38
627.41
642.45
657.48
9.83/10.02
9.60/9.75
9.39/9.45
9.18/9.25
9.83/10.13
9.60/9.79
9.39/ 9.30
9.18/9.21
9.58/9.74
9.35/9.86
9.14/9.27
8.93/9.10
60.33/60.09
60.91/60.42
61.46/61.36
61.99/61.86
64.34/64.02
64.83/64.54
65.30/65.22
65.74/65.20
64.83/65.32
65.30/65.28
65.74/65.58
65.76/65.11
4.05/4.35
4.29/4.67
4.51/4.90
4.73/5.43
4.72/4.61
4.95/4.79
5.16/5.45
5.36/5.12
4.95/4.60
5.16/5.45
5.36/5.29
6.13/6.34
4.69/4.71
4.58/4.37
4.48/4.40
4.38/4.00
10.74/10.97
10.49/10.25
10.26/10.53
10.03/9.87
10.74/10.22
10.49/9.22
10.25/9.34
10.03/10.65
10.49/10.31
10.25/10.70
10.03/9.77
9.75/10.65

P. Herich et al. / Polyhedron 28 (2009) 3565–3569
3567
Table 3
equipped with a Sapphire2 CCD detector, a monochromator En-
hance and a Cryojet cooler system, using Mo K radiation at
Crystal data and structure refinement for [Ni(dpppn)(mnt)].
a
105(2) K. CRYSALIS program package (1.171.7, Oxford Diffraction)
was used for data reduction. The structure was solved by direct
methods using SHELX programs [32,33] and refined anisotropically
for all non-hydrogen atoms by full-matrix least-squares proce-
dures. All hydrogen atoms were found from the Fourier map and
were refined isotropically. Additional calculations were performed
using the PARST program [34]. Basic X-ray data are summarized in
Tables 3–5.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
C33H30N2NiP2S2
639.36
106(2)
0.71073
P21/n
Unit cell dimensions
a (Å)
b (Å)
c (Å)
14.370(3)
13.746(3)
15.364(3)
90
a
(°)
b (°)
95.39(3)
90
3021.43(11)
4; 1.406
0.912
3. Results and discussion
c
(°)
Volume (Å3)
Z, Calculated density (Mg/m3)
3.1. Physical techniques
Absorption coefficient (mmꢂ1
F(0 0 0)
)
1328
Selected physical data for all complexes are summarized in Ta-
ble 2. Results of IR-spectroscopy show that all complexes exhibit
Crystal size (mm)
h Range for data collection (°)
Index ranges
0.30 ꢃ 0.30 ꢃ 0.20
3.05–20.0
ꢂ13 6 h 6 12,
ꢂ13 6 k 6 13,
ꢂ14 6 l 6 14
11 196/2809 [Rint = 0.0356]
94.3
vibrations typical for dithiolates
For P,P-ligands typical
v
(C–S) at 866–920 cmꢂ1 [35,36].
v
(P–CPh) vibrations [37] were found at
1433–1435 cmꢂ1 for all complexes (these vibrations for single
P,P-ligand are at 1432 cmꢂ1). A small shift can be assigned to the
coordination of both P-atoms to the central atom. Moreover, the
Reflections collected/unique
Completeness to 2
Maximum and minimum transmission
Refinement method
H = 32.14° (%)
0.8386 and 0.7714
Full-matrix least-squares on F2
2809/0/361
v
(C„N) vibrations at 2197–2204 cmꢂ1, typical of complexes I–IV
Data/restraints/parameters
with the mnt-ligand are recorded [38,39]. The planar coordination
of the nickel is also supported by electron UV/Vis absorbance spec-
troscopy; the bands of bdt and tdt complexes V–XII observed in
Goodness-of-fit on F2
1.073
R1 = 0.0295,
wR2 = 0.0740
R1 = 0.0339,
wR2 = 0.0767
0.325 and ꢂ0.235
Final R indices [I > 2
r
(I)]
the 17 180–21 120 cmꢂ1 region can be assigned to the A1g–1A2g
1
R indices (all data)
transitions typical of planar nickel(II) complexes [40]. The appro-
priate bands for complexes I–III with mnt-ligand were not ob-
served, probably due to the CT overlap appeared bands in
Largest difference in peak and hole (e Åꢂ3
)
interval 25 700–27 700 cmꢂ1
. In good accordance with the
ture of Ni(PO3)2 and Ni2P2O7 (evidence by powder X-ray diffrac-
tion). These results are not sufficient for explanation of
vulcanization activity, which proceeded under non comparable
conditions (high pressure).
The X-ray structure of [Ni(dpppn)(mnt)] (Fig. 1, Tables 3–5)
confirmed a distorted square-planar geometry of NiS2P2 chromo-
phore. The deviations of all atoms from an ideal NiS2P2 plane are
less than 0.2 Å and appropriate bond angles around central atom
are in the interval 86.46(3)–93.95(3)°. The dihedral angle between
Ni1P1P2S1S2 and Ni1S1S2C1C3 planes is 6.45(6)°. Three possible
hydrogen bond interactions between hydrogen atoms of phenyl
rings and nitrogen atoms of cyano groups were identified in the
structure.
assumption of a planar arrangement of the coordination sphere
are also the results of conductivity measurements (all complexes
are non-electrolytes) [41].
The complexes I, II, IV, V, VI, VII, VIII, IX,X, and XI are diamag-
netic, which is also in accord with the supposed square-planar
arrangement of NiS2N2 chromophore [42]; but for complexes III
and XII, a slight paramagnetism was found (see Table 2) and can-
not be eliminated by repeated purification. This fact was recently
for similar complexes described [6] and cannot be simply ex-
plained; maybe it is due to the exchange intermolecular interac-
tions of the samples [43].
The results of thermal analysis of the selected sample I (used
also for vulcanization measurements) show that the sample is sta-
ble in the range 20–340 °C (Fig. 3). Further thermal decomposition
without thermally stable intermediates is accompanied by two
sharp exo-effects at 339 and 371 °C probably due to the burning
of the sample. The final product of thermal decomposition is a mix-
Anticholinesterase activity of the selected compounds
[Ni(dppp)(tdt)], [Ni(dppp)(mnt)] and of dppp, mnt as free ligands
is shown in Table 6 and Fig. 2. The data were achieved using
biosensor technology and it was processed in Origin 6.1. The
Table 2
Results of physico-chemical study.
Compound
kM [S cm2 molꢂ1
]
UV/Vis [cmꢂ1] ꢃ 103
IR [cmꢂ1
(C–S)
]
lef [BM]
m
m(P–CPhenyl
)
m(CN)
I. [Ni(dppe)(mnt)]
II. [Ni(dppp)(mnt)]
III. [Ni(dppb)(mnt)]
IV. [Ni(dpppn)(mnt)]
V. [Ni(dppe)(bdt)]
VI. [Ni(dppp)(bdt)]
VII. [Ni(dppb)(bdt)]
VIII. [Ni(dpppn)(bdt)]
IX. [Ni(dppe)(tdt)]
X. [Ni(dppp)(tdt)]
XI. [Ni(dppb)(tdt)]
XII. [Ni(dpppn)(tdt)]
4.45
6.23
4.89
8.46
6.23
4.89
1.34
10.56
3.56
0.89
7.12
9.81
27.70
26.10
26.10
880m
920w
902w
915w
880m
866w
880m
877m
874m
867m
867m
870m
1435s
1434s
1434s
1434s
1434s
1435s
1435s
1435s
1434s
1434s
1433s
1435s
2199s
2204s
2200s
2197s
dia
dia
0.40x
dia
25.70
19.15
19.47
17.63
20.54
18.78
18.74
17.18
21.12
20.80
10.18
11.42
11.45
11.78
11.10
11.15
11.19
11.35
dia
dia
dia
dia
dia
dia
dia
0.30x
x
A slight paramagnetism cannot be removed by repeated purification.

3568
P. Herich et al. / Polyhedron 28 (2009) 3565–3569
Table 4
100
Ni(dppp)(tdt)
Ni(dppp)(mnt)
dppp
Selected bond lengths (Å) and angles (°) for [Ni(dpppn)(mnt)].
Ni(1)–S(1)
Ni(1)–S(2)
Ni(1)–P(1)
Ni(1)–P(2)
S(1)–C(1)
S(2)–C(3)
C(1)–C(3)
C(5)–P(1)
C(9)–P(2)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
2.1650(11)
2.1707(11)
2.2230(11)
2.2250(11)
1.737(3)
1.738(3)
1.357(4)
1.835(3)
1.853(3)
1.541(4)
1.531(4)
1.517(4)
1.529(4)
S(1)–Ni(1)–S(2)
P(1)–Ni(1)–P(2)
S(1)–Ni(1)–P(1)
S(2)–Ni(1)–P(2)
S(2)–Ni(1)–P(1)
S(1)–Ni(1)–P(2)
C(1)–S(1)–Ni(1)
C(3)–S(2)–Ni(1)
C(20)–P(1)–Ni(1)
C(10)–P(1)–Ni(1)
C(5)–P(1)–Ni(1)
C(9)–P(2)–Ni(1)
C(3)–C(1)–S(1)
C(2)–C(1)–S(1)
C(1)–C(3)–S(2)
C(4)–C(3)–S(2)
C(6)–C(5)–P(1)
C(8)–C(9)–P(2)
91.83(4)
80
mnt
93.98(4)
86.44(4)
88.92(4)
167.96(3)
174.35(3)
103.77(12)
103.60(11)
108.53(10)
116.20(10)
119.81(11)
118.41(11)
120.4(3)
117.7(2)
120.4(2)
119.7(2)
116.0(2)
117.7(2)
60
40
20
0
2
4
6
8
10
12
-log [c]
Fig. 2. Expression of ligands and Ni complexes anticholinesterase activity using
electrochemical biosensor. Error bars indicate standard deviation (n = 4). Data were
processed in Origin 6.1 and overlaid with sigmoidal fit.
Table 5
Possible hydrogen bonds for [Ni(dpppn)(mnt)].
Donor–H
C11–H11
0.947(24)
C13–H13
0.858(26)
C32–H32
0.972(36)
Donorꢀ ꢀ ꢀAcceptor
Hꢀ ꢀ ꢀAcceptor
Donor–Hꢀ ꢀ ꢀAcceptor
C11ꢀ ꢀ ꢀN2 (1)
H11ꢀ ꢀ ꢀN2 (1)
C11–H11ꢀ ꢀ ꢀN2 (1)
24
3.374(23)
2.486(12)
156.16(14)
TG
22
20
18
16
14
12
10
8
100
80
C13ꢀ ꢀ ꢀN1 (2)
3.351(70)
H13ꢀ ꢀ ꢀN1 (2)
2.695(54)
C13–H13ꢀ ꢀ ꢀN1 (2)
134.25(27)
C32ꢀ ꢀ ꢀN2 (3)
H32ꢀ ꢀ ꢀN2 (3)
C32–H32ꢀ ꢀ ꢀN2 (3)
3.365(49)
2.600(29)
135.75(18)
Number of possible hydrogen bonds 3.
Equivalent positions: (1) x + 1/2, ꢂy + 1/2 + 1, ꢂz + 1/2 (2) ꢂx + 1, ꢂy + 2, ꢂz + 1 (3)
60
ꢂx + 1, ꢂy + 2, ꢂz.
6
4
2
40
0
DTA
-2
-4
-6
-8
20
0
200
400
600
800
1000
Temperature (°C)
Fig. 3. Thermal analysis of [Ni(dppe)(mnt)].
Table 6
Anticholinesterase activity of selected ligands and complexes.
Compound
IC50 [M]
Mnt
Dppp
II. [Ni(dppp)(mnt)]
X. [Ni(dppp)(tdt)]
5.25 ꢃ 10ꢂ6
1.30 ꢃ 10ꢂ6
1.20 ꢃ 10ꢂ9
4.50 ꢃ 10ꢂ8
Fig. 1. ORTEP drawing of [Ni(dpppn)(mnt)] with the non-hydrogen atom labeling
scheme. Thermal ellipsoids are drawn at the 50% probability level.
after vulcanization are lower). The minimal torsion moments
(MH) are almost identical with the standard (the viscosity of rubber
mixture at the beginning of vulcanization process is almost identi-
cal). The start of vulcanization (t02 parameter) is also similar. On
the other hand, the optimal values of vulcanization (t90) of rubber
mixtures with our samples as vulcanizing agents are significantly
less than the standard value. The better activity of the vulcaniza-
tion system with our samples as dopes is confirmed by higher val-
ues of vulcanizing speed coefficients (RV). The obtained values of
solidity characteristics are almost identical with the reference
sample; the best values were reached by sample IX (Table 8),
which corresponds to the lowest values of t02 and t90 (vulcaniza-
tion process is more effective). The hardness IRHD values are
slightly lower than the hardness of reference samples, but the dif-
experiments confirmed a slow inhibition effect of dppp and mnt-li-
gands. The ligand dppp was a milder inhibitor. The ligand mnt
reached stronger anticholinesterase activity. The dissociable nickel
salt (NiSO4) alone was not found to inhibit. However, the complex
[Ni(dppp)(tdt)] acts as a strong inhibitor. The strongest inhibition
activity was displayed by the [Ni(dppp)(mnt)] complex [44].
As for the influence of selected complexes on the vulcanization
process, the basic results are summarized in Tables 7 and 8. All vul-
canizing curves are characterized by the slight reversibility. The
values of maximal torsion moments (ML) of samples are lower
compared to the standard (the viscosity values of these mixtures

P. Herich et al. / Polyhedron 28 (2009) 3565–3569
3569
Table 7
Vulcanizing characteristics of selected compounds.
Compound
MH [dN/m]
ML [dN/m]
t02 [dN/m]
t90 [dN/m]
Rv [minꢂ1
]
Santocure TBBS
13.5
13.0
14.0
15.5
104.0
92.5
95.0
92.0
3.0
2.5
3.0
2.0
15.5
12.5
12.5
12.0
8.00
10.00
10.53
10.00
I. [Ni(dppe)(mnt)]
V. [Ni(dppe)(bdt)]
IX. [Ni(dppe)(tdt)]
Table 8
Physical and mechanical properties of selected compounds.
Compound
Tensile strength [MPa]
Elongation [%]
Hardness [IRHD]
Crosslink density [mol/cm3]
Santocure TBBS
15.93
16.52
15.91
17.56
256
266
248
281
92.6
90.8
89.9
89.8
2.702 ꢃ 10ꢂ4
3.490 ꢃ 10ꢂ4
2.904 ꢃ 10ꢂ4
2.651 ꢃ 10ꢂ4
I. [Ni(dppe)(mnt)]
V. [Ni(dppe)(bdt)]
IX. [Ni(dppe)(tdt)]
ˇ
ˇ
ˇ
ˇ
[10] R. Pastorek, J. Kamenícek, M. Pavlícek, J. Husárek, Z. Šindelár, Z. Zák, Polish J.
Chem. 76 (2002) 1545.
ferences are not significant. This fact is confirmed by the lower val-
ues of viscosity rubber mixture (lower ML values, Table 7). The grid
density is a parameter that gives information about the vulcaniza-
tion network formation quality. It is connected with the number of
cross-bonds in the rubber (tire). Determination of the crosslink
density was performed by the [45] methodology; crosslink density
values are higher for samples I and V; in the case of sample IX it is
only slightly lower than the standard value.
In conclusion, all the measured samples proved to be better sul-
fur vulcanization accelerators than the commercially used sulfena-
mide type accelerator TBBS. They increase the vulcanization speed
in comparison with the standard by 20%, while the most important
physical and mechanical properties and crosslink density values
are well-kept. Moreover, the crosslink density of samples I and V,
as well as the vulcanization speed coefficients values, are better
than the standard procedure values.
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