Steric and electronic effects of substituents on planar nickel(II) complexes: Synthesis, NMR spectral and single crystal X-ray structural studies on nickel(II) dithiocarbamates with NiS2PN, NiS2PC, and NiS2P2 chromophores

Article abstract of DOI:10.1246/bcsj.79.113

Four new dithiocarbamatonickel(II) complexes [Ni(dchdtc)(NCS)(PPh ₃)] (1), [Ni(dchdtc)(CN)(PPh₃)] (2), [Ni-(dchdtc)(PPh ₃)₂]ClO₄ (3), and [Ni(dchdtc)(dppe)]ClO ₄ (4) (dchdtc = N,N-dicyclohexyldithiocarbamate anion, PPh ₃ = triphenylphosphine, and dppe = 1,2-bis(diphenylphosphino)ethane) were prepared from the parent [Ni(dchdtc)₂]. All four complexes were analyzed by CV, UV-vis, IR, and NMR (¹H, ¹³C, and ³¹P) spectra. ¹³C NMR spectra of the complexes (1-4) show the most notable >N-^...13CS₂ signals at around 200 ppm. In the cyclohexyl ring, the α-CH carbon is deshielded to a greater extent on complexation. Extraordinary deshielding was observed for the ³¹P signal in all of the cases, indicating the effective bonding of phosphorus to the metal center. Single crystal X-ray structural analysis of the mixed ligand complexes (1-3) indicates a decrease in S-Ni-S bite angle when compared to that of the parent bis(dithiocarbamate), due to an increase in steric crowding around the central metal by the introduction of a bulky PPh ₃. The trans effects on Ni-S bonds can be arranged in the following order: NCS^- < PPh₃ < CN^-. The S ₂C-^...N< bond is very short for complex 3, (1.306(3) A), because of the steric effect exerted by two PPh₃ groups and dchdtc. The observed negative reduction potentials follow the order: 1 > 2 > 3, indicating the presence of a higher relative electron density on 1 compared to 2 and 3.

Full text of DOI:10.1246/bcsj.79.113

Ó 2006 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 79, No. 1, 113–117 (2006)
113
Steric and Electronic Effects of Substituents on Planar Nickel(II)
Complexes: Synthesis, NMR Spectral and Single Crystal
X-ray Structural Studies on Nickel(II) Dithiocarbamates
with NiS2PN, NiS2PC, and NiS2P2 Chromophores
ꢀ1
Balasubramaniam Arul Prakasam,1 Kuppukkannu Ramalingam,
Gabriele Bocelli,2 and Andrea Cantoni2
1Department of Chemistry, Annamalai University, Annamalainagar - 608002, India
2IMEM, Casella Postale, Parma, Italy
Received June 29, 2005; E-mail: krauchem@yahoo.com
Four new dithiocarbamatonickel(II) complexes [Ni(dchdtc)(NCS)(PPh3)] (1), [Ni(dchdtc)(CN)(PPh3)] (2), [Ni-
(dchdtc)(PPh3)2]ClO4 (3), and [Ni(dchdtc)(dppe)]ClO4 (4) (dchdtc = N,N-dicyclohexyldithiocarbamate anion, PPh3 =
triphenylphosphine, and dppe = 1,2-bis(diphenylphosphino)ethane) were prepared from the parent [Ni(dchdtc)2]. All
four complexes were analyzed by CV, UV–vis, IR, and NMR (1H, 13C, and 31P) spectra. 13C NMR spectra of the com-
...
plexes (1–4) show the most notable >N{13CS2 signals at around 200 ppm. In the cyclohexyl ring, the ꢀ-CH carbon is
deshielded to a greater extent on complexation. Extraordinary deshielding was observed for the 31P signal in all of the
cases, indicating the effective bonding of phosphorus to the metal center. Single crystal X-ray structural analysis of the
mixed ligand complexes (1–3) indicates a decrease in S–Ni–S bite angle when compared to that of the parent bis(dithio-
carbamate), due to an increase in steric crowding around the central metal by the introduction of a bulky PPh3. The trans
...
effects on Ni–S bonds can be arranged in the following order: NCSꢁ < PPh3 < CNꢁ. The S2C{N< bond is very short
ꢀ
for complex 3, (1.306(3) A), because of the steric effect exerted by two PPh3 groups and dchdtc. The observed negative
reduction potentials follow the order: 1 > 2 > 3, indicating the presence of a higher relative electron density on 1 com-
pared to 2 and 3.
1 mmol), NiCl2 6H2O (120 mg, 0.5 mmol), and NH4SCN (75 mg,
Group 10 dithiocarbamato complexes with phosphines and
nitrogenous ligands have been in the lime light on account
of their structural novelty and their biological profiles.1 Varia-
tions in the reactivity of nickel(II) dithiocarbamates with
Lewis acids is a well documented phenomenon.2,3 The steric
and electronic nature of the dithiocarbamato ligands has a pro-
nounced effect on the reactivity of bis(dithiocarbamates) with
phosphines (both simple and chelating) and nitrogenous li-
gands.4,5 The symbiotically induced softness of substituents
on the dithiocarbamato ligands was also found to be important
when determining the reactivity.4,5 Divalent nickel complexes
of dithiocarbamates contain a planar diamagnetic MS4 chro-
mophore. Nickel(II) dithiocarbamates in their reaction with
PR3 form planar NiS2P2 chromophores, which are again dia-
magnetic in nature.6 In our continuous efforts to investigate
the synthetic and structural chemistry of dithiocarbamates,6,7
we herein report on four complexes [Ni(dchdtc)(NCS)(PPh3)]
(1), [Ni(dchdtc)(CN)(PPh3)] (2), [Ni(dchdtc)(PPh3)2]ClO4 (3),
and [Ni(dchdtc)(dppe)]ClO4 (4) (dchdtc = N,N-dicyclohexyl-
dithiocarbamate anion, PPh3 = triphenylphosphine, and
dppe = 1,2-bis(diphenylphosphino)ethane, corresponding with
NiS2PN, NiS2PC, and NiS2P2 chromophores).
ꢂ
1 mmol) was refluxed for 2 h in an acetonitrile–methanol solvent
mixture (2:1, 75 mL) and was then concentrated to ca. 50 mL.
After two days, a purple-red solid separated out from the solution.
The solid was filtered and then dried over anhydrous calcium
chloride. Single crystals suitable for X-ray diffraction were ob-
tained by repeated recrystallization of the sample from acetonitrile
(Yield 65%, dec. 192 ꢃC). Anal. Found: C, 59.94; H, 5.67; N,
4.15%. Calcd for C32H37N2NiPS3: C, 60.47; H, 5.86; N, 4.40%.
[Ni(dchdtc)(CN)(PPh3)] (2): A mixture of [Ni(dchdtc)2] (285
mg, 0.5 mmol), PPh3 (260 mg, 1 mmol), NiCl2 6H2O (120 mg, 0.5
ꢂ
mmol), and KCN (65 mg, 1 mmol) in an acetonitrile–methanol
(2:1, 75 mL) solvent mixture was refluxed for 3 h. The resulting
orange-red solution was filtered and the filtrate was left undis-
turbed for two days. After two days, an orange-red solid separated
out. Single crystals suitable for X-ray analysis were obtained by
recrystallization of the sample from the same solvent mixture
(Yield 65%, dec. 198 ꢃC). Anal. Found: C, 62.99; H, 6.01; N,
4.44%. Calcd for C32H37N2NiPS2: C, 63.68; H, 6.17; N, 4.63%.
[Ni(dchdtc)(PPh3)2]ClO4 (3): A mixture of [Ni(dchdtc)2]
(285 mg, 0.5 mmol), PPh3 (520 mg, 2 mmol), NiCl2 6H2O (120
ꢂ
mg, 0.5 mmol), and NH4ClO4 (115 mg, 1 mmol) was refluxed for
about 2 h in an acetonitrile–dichloromethane solvent mixture (1:1,
50 mL), and was then concentrated to ca. 25 mL. After two days, a
purple-red solid separated out from the solution. The solid was
filtered and then dried over anhydrous calcium chloride. Single
crystals suitable for X-ray diffraction were obtained by recrys-
Experimental
Preparation of Complexes. [Ni(dchdtc)(NCS)(PPh3)] (1):
A mixture of [Ni(dchdtc)2] (285 mg, 0.5 mmol), PPh3 (260 mg,
Published on the web January 13, 2006; DOI 10.1246/bcsj.79.113

114 Bull. Chem. Soc. Jpn. Vol. 79, No. 1 (2006)
Table 1. NMR Spectral Data (Chemical Shifts in ppm)
Steric and Electronic Effects in Planar NiS2A2
aÞ
Complex
NMR
ꢀ-CH
ꢃ-CH2
ꢄ-CH2
ꢅ-CH2
PPhx
>N13CS2
1H
13C
31P
1.14–1.85
7.45–7.72
128.7–134.2
22.8
—
201.9bÞ
—
1
60.5
—
29.6
—
24.9
—
25.8
—
1H
13C
31P
1.17–1.82
7.40–7.72
128.5–134.3
30.3
—
203.5bÞ
—
2
3
4
60.8
—
29.7
—
24.9
—
25.9
—
1H
13C
31P
1.16–1.78
7.28–7.46
127.5–134.2
31.5
61.2
—
29.8
—
24.7
—
25.6
—
197.8
—
1H
13C
31P
1.22–3.08
7.52–8.24
127.2–133.6
59.9
—
201.0
—
54.0
—
24.0
—
24.6
—
24.8
—
a) Where x ¼ 3 for 1, 2, and 3 and 2 for 4. b) S–13C–N signal of 1 and 13CN signal of 2 are observed
respectively at 143.3 and 130 ppm.
tallization of the sample from acetonitrile (Yield 70%, dec.
187 ꢃC). Anal. Found: C, 62.19; H, 5.48; N, 1.41%. Calcd for
C49H52ClNNiO4P2S2: C, 62.65; H, 5.58; N, 1.49%.
by request quoting the deposition number from, The Director,
CCDC, 12, Union Road, Cambridge, CB2 1EZ, UK (fax: +44
1223 336033; E-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk/conts/retrieving.html).
[Ni(dchdtc)(dppe)]ClO4 (4):
(570 mg, 1 mmol), dppe (790 mg, 2 mmol), NiCl2 6H2O (240 mg,
A mixture of [Ni(dchdtc)2]
ꢂ
1 mmol), and NH4ClO4 (230 mg, 2 mmol) was refluxed for about
4 h in a methanol–dichloromethane solvent mixture (1:1, 50 mL),
followed by concentration to ca. 25 mL. After 2 days, a purple-red
solid separated out and was dried over anhydrous calcium chloride.
The solid was recrystallized from the same solvent mixture (Yield
65%, dec. 183 ꢃC). Anal. Found: C, 57.25; H, 5.59; N, 1.62%.
Calcd for C39H46ClNNiO4P2S2: C, 57.60; H, 5.70; N, 1.72%.
Results and Discussion
Electronic Spectra. Electronic spectra show bands at 475,
439, 510, and 471 nm for complexes 1, 2, 3, and 4, respective-
ly, due to d–d transitions. Based on the single crystal electronic
spectral studies of similar complexes, the band around 470 nm
for complexes 1 and 4 is attributed to the dz2 ! dx2ꢁy2 tran-
sition9 and the cyanide ion exerting a larger LFSE, resulting
in the least ꢁmax being associated with 2. In all of the cases
the charge-transfer bands were observed below 400 nm.9 Elec-
tronic spectral data of the complexes support the assumption of
a square planar geometry around the nickel atom in all of the
complexes.
Instrumentation and Methods.
All of the reagents and
solvents employed were commercially available analytical grade
materials and were used as supplied without further purification.
Electronic spectra of the complexes were recorded on a HITACHI
U-2001 spectrophotometer using CH2Cl2 as the solvent. IR spec-
tra were recorded on an ABB Bomem MB 104 spectrophotometer
(range 4000–400 cmꢁ1) as KBr pellets. Cyclic voltammograms
were recorded in CH2Cl2 (10ꢁ3 M) on an ECDA basic electro-
chemical system comprising of glassy carbon as the working elec-
trode, Ag/Agþ as the reference electrode, and Pt wire as the coun-
ter electrode. NMR spectra of all four complexes were recorded
on a Bruker AMX 400 spectrometer at room temperature, using
CDCl3 as the solvent and TMS as the internal reference. The
13C NMR spectra were recorded in proton decoupled mode. The
1H, 13C, and 31P chemical shifts and their corresponding assign-
ments are given in Table 1.
X-ray Crystallography. Details of crystal data, data collec-
tion, and refinement parameters for complexes 1, 2, and 3 are
summarized in Table 2. Intensity data were collected at ambient
temperature (295 K) on a Bruker AXS (with CCD) diffractometer
using graphite monochromated Mo Kꢀ radiation. Absorption cor-
rection was performed with a method inserted into SHELXL-NT
V.5.1.8 The Bruker AXS software was used for solving structures.
All of the non-hydrogen atoms were refined anisotropically and all
of the hydrogen atoms were refined isotropically. Selected bond
lengths and bond angles are given in Table 3.
IR Spectral Studies. The parent [Ni(dchdtc)2] shows a
ꢂC{N band at 1462 cmꢁ1, whereas the same band appears at
1503, 1506, 1510, and 1499 cmꢁ1 for complexes 1, 2, 3, and
4, respectively. This is because of the significant contribution
...
made by the polar S2Cꢁ {Nþ< structure in all of the cases.
Increasing drift of electron density from the dithiocarbamate
...
towards the metal center moves the ꢂC{N (S2C{N<) stretching
bands progressively to higher frequencies. The band resulting
from the ‘‘N’’-coordination of the thiocyanato-N ligand in 1
appears at 2092 cmꢁ1. Similarly for compound 2, the band at
2108 cmꢁ1 is evidence of the coordination of the cyanide ion
and the metal center through carbon. In the present study, the
occurrence of a single ꢂC{S band in the region of 990–1000
cmꢁ1 for all of the complexes indicates the uninegative biden-
tate behavior of the dithiocarbamato ligand.
NMR Spectral Studies. 1H NMR: Since the ꢀ, ꢃ, and ꢄ
(a, e) protons of the cyclohexyl ring give only a multiplet, in the
table only the region in which cyclohexyl ring proton signals
were observed is given, and no individual assignments were
made. For all four (1–4) complexes, the aromatic protons from
triphenylphosphine and chelating dppe resonate in the region of
7.28–8.24 ppm. In the case of complex 4, the signal for the CH2
in dppe also merged with the cyclohexyl ring proton signals.
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Collection Centre: Deposition numbers
CCDC-263871, -263872, and -263873 for complexes 1, 2, and 3,
respectively. Copies of the data can be obtained free of charge

B. Arul Prakasam et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 1 (2006)
115
Table 2. Crystal Data, Data Collection, and Refinement Parameters for 1, 2, and 3
Complex
1
2
3
Empirical formula
FW
C32H37N2NiPS3
635.5
C32H37N2NiPS2
603.5
0:17 ꢄ 0:19 ꢄ 0:21
Hexagonal
Orange-red
P31
C49H52ClNNiO4P2S2
939.2
Crystal dimensions/mm3 0:23 ꢄ 0:31 ꢄ 0:39
0:15 ꢄ 0:30 ꢄ 0:36
Crystal system
Colour
Space group
Monoclinic
Purple-red
P21=c
12.745(2)
10.474(2)
25.765(3)
90
98.67(2)
90
3400.1(9)
4
1.241
Orthorhombic
Purple
Pbca
15.488(3)
37.392(4)
16.571(3)
90
90
90
9596.7(3)
8
1.297
6.57
3936
ꢀ
a/A
16.124(2)
16.124(2)
10.185(2)
90
90
120
2293.2(6)
3
1.311
8.47
954
ꢀ
b/A
ꢀ
c/A
ꢀ/ꢃ
ꢃ/ꢃ
ꢄ/ꢃ
ꢀ 3
U/A
Z
Dcalcd/g cmꢁ3
ꢆ/cmꢁ1
Fð000Þ
8.24
1336
ꢀ
ꢁ/A
Mo Kꢀ (0.71069)
1.62–28.61
! ꢁ 2ꢇ
Mo Kꢀ (0.71073)
2.48–23.99
! ꢁ 2ꢇ
Mo Kꢀ (0.71073)
1.09–28.56
! ꢁ 2ꢇ
ꢇ range/ꢃ
Scan type
ꢁ15 ꢅ h ꢅ 16, ꢁ10 ꢅ k ꢅ 13, ꢁ11 ꢅ h ꢅ 10, ꢁ4 ꢅ k ꢅ 11,
0 ꢅ h ꢅ 20, 0 ꢅ k ꢅ 49,
0 ꢅ l ꢅ 22
11273
Index ranges
ꢁ33 ꢅ l ꢅ 32
ꢁ7 ꢅ l ꢅ 9
Reflections collected
Observed reflections
F0 > 4ꢈðF0Þ
6644
1463
1985
1384
7484
2
2
2
2
2
2
W ¼ 1=½ꢈ2ðF0 Þ þ ð0:0302PÞ
W ¼ 1=½ꢈ2ðF0 Þ þ ð0:0334PÞ
W ¼ 1=½ꢈ2ðF0 Þ þ ð0:0867PÞ
Weighting scheme
þ 0:000Pꢆ
þ 0:00Pꢆ
þ 0:000Pꢆ
2
2
2
2
2
2
where P ¼ ðF0 þ 2Fc Þ=3
478
where P ¼ ðF0 þ 2Fc Þ=3
467
where P ¼ ðF0 þ 2Fc Þ=3
749
Number of parameters
refined
Final R, Rw (obs, data)
GOOF
0.0567, 0.0841
0.721
0.0185, 0.0431
0.973
0.0322, 0.1068
0.860
Table 3. Selected Bond Distances and Bond Angles for 1, 2, and 3
1
2
3
ꢀ
Bond distances/A
Ni1–N18
Ni1–S2
Ni1–P21
Ni1–S3
S2–C4
S3–C4
C4–N5
N5–C12
N5–C6
1.878(6)
2.1751(17)
2.196(2)
2.2041(19)
1.705(6)
1.724(6)
1.350(7)
1.493(7)
1.476(7)
Ni–C1
Ni–S3
Ni–P2
Ni–S4
S3–C20
S4–C20
C20–N2
N2–C21
N2–C27
1.878(9)
2.189(2)
2.205(2)
2.211(2)
1.722(7)
1.745(7)
1.320(8)
1.478(9)
1.499(8)
Ni1–S3
Ni1–P18
Ni1–S2
Ni1–P37
S2–C4
2.1914(7)
2.2110(7)
2.2141(7)
2.2525(7)
1.736(2)
1.717(3)
1.306(3)
1.495(3)
1.526(4)
S3–C4
C4–N5
N5–C6
N5–C12
Bond angles/ꢃ
N18–Ni1–S2
N18–Ni1–P21
S2–Ni1–P21
N18–Ni1–S3
S2–Ni1–S3
P21–Ni1–S3
C4–S2–Ni1
C4–S3–Ni1
N5–C4–S2
172.43(17)
91.87(17)
95.62(7)
94.36(17)
78.23(7)
173.14(7)
87.9(2)
C1–Ni–S3
C1–Ni–P2
S3–Ni–P2
C1–Ni–S4
S3–Ni–S4
P2–Ni–S4
C20–S4–Ni
C20–S3–Ni
N2–C20–S3
N2–C20–S4
S3–C20–S4
90.0(2)
95.3(2)
S3–Ni1–P18
S3–Ni1–S2
P18–Ni1–S2
S3–Ni1–P37
P18–Ni1–P37
S2–Ni1–P37
C4–S2–Ni1
C4–S3–Ni1
N5–C4–S3
N5–C4–S2
S3–C4–S2
170.38(3)
77.71(3)
93.11(3)
169.28(9)
168.2(2)
78.56(7)
96.47(8)
86.6(3)
89.05(3)
100.20(2)
166.63(3)
87.06(8)
86.5(2)
87.9(3)
88.26(8)
127.9(5)
124.7(5)
107.3(3)
126.6(5)
126.4(5)
106.9(5)
127.23(19)
126.43(19)
106.33(14)
N5–C4–S3
S2–C4–S3

116 Bull. Chem. Soc. Jpn. Vol. 79, No. 1 (2006)
Steric and Electronic Effects in Planar NiS2A2
13C NMR: As observed earlier,10 the dithiocarbamates that
...
show high ꢂC{N (S2C{N<) band values in IR spectrum have
a corresponding low >N13CS2 chemical shifts in 13C NMR
spectrum and vice versa. In the cyclohexyl ring, the ꢀ-CH car-
bon appears to be deshielded to a greater extent and signals are
observed at 60.5, 60.8, 61.2, and 54.0 ppm for complexes 1, 2,
3, and 4, respectively. Among the ꢄ-CH2 and ꢅ-CH2 carbons,
the ꢅ-CH2 carbon signals are observed in the up field region
(of around 1 ppm) relative to that of ꢄ-CH2 carbon signals with
comparatively low intensity. An up field shift is generally
observed for any carbon that exists in gauche orientation with
respect to another carbon or hetero atom, relative to the shield-
ing of its anti counterpart.11
Fig. 1. ORTEP of [Ni(dchdtc)(PPh3)(NCS)].
31P NMR: Generally, free triphenylphosphine shows a sig-
nal at ꢁ5 ppm11 and a coordinated phosphine shows a signal at
around 20 ppm. Similarly, free chelating dppe shows a signal
at ꢁ13 ppm12 and a coordinated chelating phosphine shows a
signal at around 60 ppm. The complex with chelating dppe
gives a signal at 59.9 ppm for the coordinated phosphorus.
An increase in negative charge on phosphorus by the direct
bonding of the electron donating methylene group may force
the alleviation of excess electron density (from the chelating
dppe) to the metal center, in contrast to those of complexes
with free PPh3 (1–3) where phosphorus is attached to electron
withdrawing phenyl groups. Similarly, there is an interesting
correlation between the ꢁmax of d–d bands observed in the
complexes with the nature of phosphine involved in the com-
plex. The presence of two PPh3 groups in complex 3 shows a
larger ꢁmax value compared to that of the chelating dppe ana-
logue 4. The observation is in line with the observed 31P NMR
chemical shift values. More than the binding ability, two mole-
cules of PPh3 in the place of dppe destabilize the complex due
to their steric demand. Higher relative deshielding is observed
in the case of complexes with NiS2P2 and NiS2PC chromo-
phores. Very high deshielding is observed for the 31P signal
in all of the cases, indicating the drift of electron density from
phosphorus on complexation.
Fig. 2. ORTEP of [Ni(dchdtc)(PPh3)(CN)].
differ considerably from 90ꢃ [S(2)–Ni(1)–P(21) = 95.62(7);
N(18)–Ni(1)–S(3) = 94.36(17);
N(18)–Ni(1)–P(21) =
91.87(17); S(2)–Ni(1)–S(3) = 78.23(7)ꢃ]. The molecule is
not perfectly square planar because of the small bite angle of
78.23(7)ꢃ. The two Ni–S [Ni(1)–S(2) = 2.1751(17) and
ꢀ
Ni(1)–S(3) = 2.2041(19) A] and C–S [C(4)–S(2) = 1.705(6)
ꢀ
and C(4)–S(3) = 1.724(6) A] distances are asymmetric due
to the difference in the trans influencing property of the NCSꢁ
and PPh3 groups. The delocalization of the ꢉ electron density
over the S2CN moiety results in the strong double bond char-
ꢀ
acter of the [C(4)–N(5) = 1.350(7) A] bond, which is also sup-
ported by the observed increase in S–C–N angles [124.7(5)
and 127.9(5)ꢃ] over the S–C–S angle of 107.3(3)ꢃ. The N–
C–S bond angle of the thiocyanato-N [177.3(7)ꢃ] exemplifies
the linear nature of the N–C–S fragment. The packing diagram
of the molecule shows that the cyclohexyl rings of the dithio-
carbamate and the phenyl rings of the PPh3 molecules are
found well stacked, one over the other, along the OB axis of
the unit cell, enabling an effective three-dimensional arrange-
ment for the molecule. The two cyclohexyl rings appear to be
bonded to the nitrogen equatorially and the phenyl rings in the
triphenylphosphine show normal bond parameters.
[Ni(dchdtc)(CN)(PPh3)] (2) is monomeric with no signifi-
cant intermolecular associations. ORTEP of the complex is
shown in Fig. 2. Three formula units are present in the unit
cell. The planar environment around the central metal atom
is well supported by the small mean plane deviation of S(3)
Cyclic Voltammetric Studies. From the CV studies, it
was observed that all of the complexes undergo a one electron
reduction process (NiII ! NiI). All four mixed ligand com-
plexes have lower reduction potentials [ꢁ1310, ꢁ1246, ꢁ1180,
and ꢁ890=ꢁ801 mV for 1, 2, 3, and 4, respectively] than the
parent Ni(dchdtc)2 [ꢁ1580 mV], which shows a reluctance to
add more electron density to the already electron rich metal
center in the parent complex. For complex 4, a quasi-reversible
c
a
reduction couple [Ep ¼ ꢁ890 mV/Ep ¼ ꢁ801 mV] is ob-
served, and this observation is a phenomenon due to the che-
lating phosphine which stabilizes the reduced NiI complexes.6
Gradation of the observed negative reduction potentials viz,
1 > 2 > 3, indicates the presence of a higher relative electron
density on 1 compared to 2 and 3.
Structural Analysis. Single crystal X-ray structural analy-
sis of complexes 1, 2, and 3 are discussed here, our attempts to
crystallize complex 4 having been unsuccessful. The ORTEP
diagram of [Ni(dchdtc)(NCS)(PPh3)] (1) is shown in Fig. 1
together with the atom numbering scheme. The structure con-
sists of a distorted square planar metal coordination with the
NiS2PN chromophore. For 1, the coordination sphere shows
only minor deviations from planarity, but with angles that
ꢀ
of 0.142 A. The bite angle associated with the dithiocarbamate
is very small [S–Ni–S = 78.56(7)ꢃ]. Ni–S [Ni–S(3) = 2.189(2)
ꢀ
and Ni–S(4) = 2.211(2) A] and C–S [C(20)–S(3) = 1.722(7)
ꢀ
and C(20)–S(4) = 1.745(7) A] distances are symmetrical. The
ꢀ
C–N bond length [1.134(8) A] in the cyanide moiety is shorter
...
ꢀ
than the [>N{CS2] C–N distance of 1.320(8) A, indicating its
triple bonded nature. The increase in P–Ni–C [95.3(2)ꢃ] and

B. Arul Prakasam et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 1 (2006)
117
ꢀ
the Cl–O distances vary from 1.129(8) to 1.424(6) A, and the
O–Cl–O angles vary from 102.8(5) to 116.8(9)ꢃ, indicating a
deviation from an ideal tetrahedral geometry. The perchlorate
anion shows extensive thermal disorder as observed in many
similar compounds.
Comparison of Bond Parameters. The decrease in the
S–Ni–S bite angle for all of the mixed ligand complexes com-
pared to that of the parent [79.06(5)ꢃ] bisdithiocarbamate13 is
due to the increase in steric crowding around the metal center
by the introduction of bulky PPh3 in the cases of complexes 1,
2, and 3. The S–Ni–S bite angle and the [>NCS2] C–N bond
distance are very small for complex 3, a clear manifestation of
the steric crowding caused by the two bulky PPh3 groups, and
to some extent by the bulky nature of the two cyclohexyl rings
attached to the dithiocarbamate. P–Ni–N (1) and P–Ni–C (2)
angles are smaller than the P–Ni–P angle in 3 because of the
sterically less demanding NCSꢁ and CNꢁ present in 1 and 2,
respectively, in the place of bulky PPh3.
Fig. 3. ORTEP of [Ni(dchdtc)(PPh3)2]ClO4 (hydrogen
atoms and ClO4 anion are omitted for clarity).
P–Ni–S [96.47(8)ꢃ] angles over the other two angles [C(1)–
Ni–S(3) = 90.0(2)ꢃ and S(4)–Ni–S(3) = 78.56(7)ꢃ] around
the metal center exemplifies the steric effect exerted by the
bulkier PPh3. The Ni–C–N angle [174.4(7)ꢃ] is slightly non-
linear because of the presence of bulky PPh3 in the adjacent
position.
References
1 P. S. Jarrett, O. M. N. Dhubhghaill, P. J. Sadler, J. Chem.
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2
3
4
5
A. Chakravorty, Prog. Inorg. Chem. 1996, 7, 83.
J. P. Fackler, Jr., W. C. Seidel, Inorg. Chem. 1969, 8, 1631.
C. K. Jorgensen, Inorg. Chem. 1964, 3, 1201.
ORTEP of complex 3 is shown in Fig. 3. The observed
planarity of the NiS2P2 chromophore in this molecule is con-
sistent with the diamagnetic nature of the complex. For nickel,
the two sulfur atoms from the dithiocarbamate part and two
phosphorus atoms from the triphenylphosphine ligand form
an approximate square planar arrangement with the small bite
angle associated with the dithiocarbamate moiety [77.71(3)ꢃ].
The observed reduction in bite angle is attributed to the very
high steric effect caused by the two triphenylphosphine ligands
and the two cyclohexyl rings of the dithiocarbamate. The Ni–P
K. Ramalingam, G. Aravamudan, V. Venkatachalam, Bull.
Chem. Soc. Jpn. 1993, 66, 1554.
R. Thiruneelakandan, K. Ramalingam, G. Bocelli, A.
Cantoni, Z. Anorg. Allg. Chem. 2005, in press.
V. Venkatachalam, K. Ramalingam, R. Akilan, K.
Sivakuamr, K. Chinnakali, H. K. Fun, Polyhedron 1996, 15, 1289.
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6
7
8
ꢀ
distances [2.2110(7) and 2.2525(7) A] are asymmetric. As in 1,
2, and in the case of complex 3 also, two cyclohexyl rings are
stacked in chair conformation. The Ni–S [2.1914(7) and
9
M. V. Rajasekaran, G. V. R. Chandramouli, P. T.
Manoharan, Chem. Phys. Lett. 1989, 162, 110.
10 H. L. M. Van Gaal, J. W. Diesveld, F. W. Pijpers, J. G. M.
Van Der Lindon, Inorg. Chem. 1979, 18, 3251.
11 R. M. Silverstein, F. X. Webster, Spectrometric Identifica-
tion of Organic Compounds, 6th ed., John Wiley & Sons Inc.,
New York, 1998.
ꢀ
ꢀ
2.2141(7) A] and C–S [1.736(2) and 1.717(3) A] bonds are
almost symmetrical, indicating delocalization of the negative
charge on the dithiocarbamate ligand. The two S–C–N angles
[127.23(19) and 126.43(19)ꢃ] are about 20ꢃ higher than the
S–C–S angle [106.33(14)ꢃ]. The C–P–C angles in the triphen-
ylphosphines are asymmetric [102.04(10) to 110.91(13)ꢃ] due
to the steric crowding of the phenyl rings. In the counter anion,
12 E. P. Garrou, Chem. Rev. 1981, 81, 229.
13 M. J. Cox, E. R. T. Tiekink, Z. Kristallogr. 1999, 214, 242.