Trans influence of triphenylphosphines and pseudohalogens on Ni-S bonds: Synthesis, spectral and single crystal X-ray structural studies on NiS 2PN and NiS2PC chromophores

Article abstract of DOI:10.2478/s11532-012-0041-2

Trans influence of triphenylphosphines and pseudohalogens on Ni-S bonds of NiS₂PN and NiS₂PC chromophores has been investigated by synthesizing and characterizing them. The complexes show the characteristic thioureide IR band at ~ 1530 cm^-1. Electronic spectrum of the cyanide analogue shows a strong blue shift relative to others. X-ray structures of [Ni(pipdtc)(4-MP)(NCS)] (1), [Ni(pipdtc)(PPh₃)(NCS)] (2) and [Ni(pipdtc)(PPh₃)(CN)] (3) (pipdtc = piperidinecarbodithioate anion, 4-MP = tri(4-methylphenyl) phopshine) are reported. Ni-S bond distance trans to 4-MP(1) is longer than the distances in (2) and (3) and Ni-S bond distances trans to Ni-NCS/CN decrease as follows: (3) > (2) > (1). Particularly, 4-MP shows a highly significant trans influence than triphenylphosphine on Ni-S bond. Similarly, CN- exerts a marginally significant trans influence compared to NCS-. Thioureide C-N distances are relatively very short due to the drift of electron density towards the metal. The Ni-N-C angle (163.5(2)°) observed in (2) indicates deviation from linearity to a larger extent compared to that in (1) (176.3(3)°) due to the steric effect of the 4-methyl group. The reduction potentials (CV) for the mixed ligand complexes are much less compared to that of the parent NiS₄ chromophore due to the-acidic phosphines. Versita Sp. z o.o.

Full text of DOI:10.2478/s11532-012-0041-2

Cent. Eur. J. Chem. • 10(4) • 2012 • 1199-1207
DOI: 10.2478/s11532-012-0041-2
Central European Journal of Chemistry
Trans influence of triphenylphosphines
and pseudohalogens on Ni-S bonds:
Synthesis, spectral and single crystal
X-ray structural studies on NiS2PN
and NiS2PC chromophores
Research Article
Kuppukkannu Ramalingam1*, Raghavan Thiruneelakandan2,
Gabriele Bocelli3, Lara Righi3
1Department of Chemistry, Annamalai University,
Annamalainagar 608 002, India
2Department of Chemistry, Anna University of Technology,
Tiruchirappalli 620 024, India
3IMEM-CNR, Parco Area Delle Scienze, Parma 43100, Italy,
Received 2 December 2011; Accepted 16 February 2012
Abstract:
Trans influence of triphenylphosphines and pseudohalogens on Ni-S bonds of NiS2PN and NiS2PC chromophores has been investigated
by synthesizing and characterizing them. The complexes show the characteristic thioureide IR band at ~ 1530 cm-1. Electronic
spectrum of the cyanide analogue shows a strong blue shift relative to others. X-ray structures of [Ni(pipdtc)(4-MP)(NCS)] (1),
[Ni(pipdtc)(PPh3)(NCS)] (2) and [Ni(pipdtc)(PPh3)(CN)] (3) (pipdtc = piperidinecarbodithioate anion, 4-MP = tri(4-methylphenyl)
phopshine) are reported. Ni—S bond distance trans to 4-MP(1) is longer than the distances in (2) and (3) and Ni—S bond
distances trans to Ni—NCS/CN decrease as follows: (3) > (2) > (1). Particularly, 4-MP shows a highly significant trans influence
than triphenylphosphine on Ni-S bond. Similarly, CN- exerts a marginally significant trans influence compared to NCS-. Thioureide C—N
distances are relatively very short due to the drift of electron density towards the metal. The Ni—N—C angle (163.5(2)°) observed in
(2) indicates deviation from linearity to a larger extent compared to that in (1) (176.3(3)°) due to the steric effect of the 4-methyl group.
The reduction potentials (CV) for the mixed ligand complexes are much less compared to that of the parent NiS4 chromophore due to
the π-acidic phosphines.
Keywords: Nickel(II) • Trans influence • Cyanide • Thioureide • X-ray crystal structure.
© Versita Sp. z o.o.
show asymmetry in Ni-S bonds due to variations in the
1. Introduction
nature of the substituents [5,6]. NiS4 chromophore of the
dithiocarbamates react with substituted phosphines with
ease to form [Ni(dtc) PR3X] complexes. A number of
complexes of the general formula, [Ni(dtc)PR3X] where,
dtc=S2CN(C2H5)2,S2CN(CH3)(C2H4OH),S2CN(C2H4OH)2,
S2CN(C3H7)2, S2CN(C5H10)2 and X = Cl, SCN, CN have
been synthesized and structurally characterized from
our laboratory [7-10]. Paticularly, electronic spectra of
the [Ni(dtc)(PPh3)X] are highly sensitive to the nature
of ‘X’ ligand and single crystal X-ray structures of (dtc
Coordination complexes involving group X metal ions,
dithiocarbamates, phosphines and different nitrogenous
bases exhibit interesting structural variations [1].
Some of the dithiocarabamates find applications in the
field of medicine [2]. Divalent nickel is a ‘borderline
acid’ which softens on coordination with soft sulphur
atoms of the dithiocarbamate facilitating its reaction
with soft donors [3,4]. Bis(dithiocabamato) nickel(II)
complexes are planar, diamagnetic and invariably
* E-mail: krauchem@yahoo.com
1199

Trans influence of triphenylphosphines and pseudohalogens
on Ni-S bonds: Synthesis, spectral and single crystal X-ray
structural studies on NiS2PN and NiS2PC chromophores
= ethylcyclohexyldithiocarbamate) indicate that the (2:1, 50 mL) was refluxed for 3 hours, followed by
planar environment of the complexes is amenable concentration to ca. 25 mLand was then left undisturbed
to tetrahedral distortions due to steric influence [11]. for two days. The precipitated orange yellow compound
Reports on trans influences on the distortions in planar was filtered and dried over anhydrous calcium chloride.
[Ni(dtc)(PPh3)X] chromophores is limited and in Single crystals suitable for X-ray analysis were obtained
continuation of our interest [12,13] in understanding by recrystallization from CH3OH-CH3CN solvent mixture.
the factors controlling the structure of [Ni(dtc)(PPh3)X] Crystals obtained were unstable at room temperature
chromophores,hereinwereportthesynthesis,spectraland and hence they were kept under liquid paraffin.
structural characterization of [Ni(pipdtc)(4-MP)(NCS)] Yield: 55%; m.p.: 149°C (dec.). Analytical data
(1), [Ni(pipdtc)(PPh3)(NCS)](2) and [Ni(pipdtc)(PPh3) (for solvent free complex) C25H25N2NiPS2 (507.3) calcd.:
(CN)](3) (where pipdtc = piperidinedithiocarbamate; 59.18% C, 5.00% H, 5.52% N; found: 59.14% C, 4.96%
4-MP = tri(4-methylphenyl)phosphine).
H, 4.96% N.
2.2. Cyclic voltammetry
2. Experimental procedure
ECDA-001 Basic Electrochemistry system was used
for all measurements. Glassy carbon was used as
All the reagents and solvents employed were working electrode and the counter electrode was a
commercially available high-grade purity materials platinum wire. Electrochemical grade CH2Cl2 was used
(E-Merck) used as supplied without further purification. as the solvent. The reference electrode was Ag/AgCl.
IR spectra were recorded on Avator Nicolet FT-IR Tetrabutylammonium perchlorate (0.01 M) was used as
spectrometer (range: 4000 – 400 cm—1) as KBr pellets. the supporting electrolyte. The experiments were carried
The UV-Visible spectra in CH2Cl2 were recorded in a out in an oxygen free atmosphere by bubbling purified
Hitachi U-2001 double beam spectrophotometer.
nitrogen gas through the solution at room temperature.
The peak potentials showed a maximum variation
of +/- 5 mV.
2.1. Preparation
2.1.1. [Ni(pipdtc)(4-MP)(NCS)] (1)
The parent complex, [Ni(pipdtc)2] was prepared [14]
and was recrystallized from ethanol. A mixture of
[Ni(pipdtc)2](380 mg, 1 mmol), 4-MP (610 mg, 2 mmol),
NiCl2•6H2O (240 mg, 1 mmol) and NH4SCN (150 mg,
2 mmol) in acetonitrile - methanol (1:1, 50 mL) was
refluxed for about 3 hours, followed by concentration to
ca. 25 mL. The precipitated purple red compound was
filtered and was dried over anhydrous calcium chloride.
Single crystals suitable for X-ray analysis were obtained
by recrystallization from acetonitrile. Yield: 70%; m.p.:
147°C (dec.). For C28H31N2Ni PS3 (581.4) calcd.: 57.83%
C, 5.38% H, and 4.82% N; found: 57.80% C, 5.80% H,
4.79% N.
2.3. X-ray crystallography
Details of crystal data, data collection and refinement
parameters for the compounds are given in Table 1 and
selected bond parameters are listed in Table 2. Intensity
data were collected at ambient temperature (293 K) on
Bruker AXS smart single crystal diffractometer with CCD
(area detector) by using graphite-monochromated Mo-
Kα radiation (λ = 0.71069 Å). The structure was solved
by direct method inserted in SHELXTL-NT V5.1 in the
Bruker AXS software [15] and the molecular diagrams
were drawn with ORTEP – 3 program [16].
3. Results and discussion
2.1.2. [Ni(pipdtc)(PPh3)(NCS)] (2)
A mixture of Ni(pipdtc)2 (380 mg, 1 mmol), PPh3 (520 mg, 3.1. IR and electronic spectra
2 mmol), NiCl2•6H2O (240 mg, 1 mmol) and NH4SCN IR spectra of complexes (1), (2) and (3) show thioureide
(150 mg, 2 mmol) in acetonitrile - methanol (1:1, 50 mL) ν(C-N) bands at 1532, 1531 and 1533 cm-1 . The parent
was refluxed for about 3 hours, followed by concentration bisdithiocarbamate, [Ni(pipdtc)2] shows the thioureide
to ca. 25 mL and was left undisturbed for two days. The band at 1508 cm-1 [14]. The shift in νC-N value to higher
precipitated purple red compound was filtered and dried wave number compared to the parent dithiocarbamate
over anhydrous calcium chloride. Single crystals suitable is due to increased mesomeric drift of electron density
for X-ray analysis were obtained by recrystallization from the dithiocarbamate moiety towards the metal
from acetonitrile. Yield: 70%; m.p.: 152°C (dec.). atom. The ν(C-S)
bands appear at 1017, 1013 and
1009 cm-1 for complexes (1), (2) and (3) respectively
without any splitting [17]. The ν(N-C(-S))band appears
at 2090 and 2089 cm-1 for (1) and (2) respectively. The
ν(C-N) band for the cyanide appears at 2116 cm-1 for
compound (3). Electronic spectra of (1) and (2) show
bands at ~400 nm due to charge transfer with large
optical densities. Another band observed at 478 nm
For C25H25N2 NiPS3 (539.3) calcd.: 55.66% C, 4.68% H,
5.19% N; found: 55.63% C, 4.64% H, 5.17% N.
2.1.3. [Ni(pipdtc)(PPh3)(CN)] (3)
A mixture of [Ni(pipdtc)2] (380 mg, 1 mmol), PPh3
(520 mg, 2 mmol), NiCl2•6H2O (240 mg, 1 mmol)
and KCN (130 mg, 2 mmol) in methanol-acetonitrile
1200

K. Ramalingam et al.
Table 1. Crystal data, data collection and refinement parameters of (1), (2) and (3).
Complex
(1)
(2)
(3)
Empirical formula
FW
C28H31N2Ni PS3
581.4
C25H25N2Ni PS3
539.3
C27H25N3Ni PS2
545.3
Crystal dimensions/mm
Crystal system
0.19×0.29×0.33
Triclinic
0.19×0.27×0.33
Triclinic
0.14×0.19×0.31
Triclinic
Space group
P1
P1
P1
a/Å
12.338(3)
15.754(4)
15.761(3)
96.55(4)
101.17(2)
99.56(3)
2929.7
10.483(3)
13.334(2)
10.379(3)
105.56(3)
112.18(2)
73.26(3)
1265.5
9.389(2)
15.494 (3)
9.240(3)
92.53(3)
97.60(3)
84.35 (2)
1325.2
2
b/Å
c/Å
α/°
β/°
γ/°
V/Å3
Z
4
2
Dc/g cm-3
µ/cm-1
1.318
1.415
1.367
9.50
10.93
9.70
λ/Å
Mo-Kα (0.71069)
3 – 28
Mo-Kα (0.71069)
3-30
Mo-Kα (0.71069)
3-30
Θ range/°
Scan type
Reflections collected
-2θ
-2θ
-2θ
12750
6866
7715
Observed reflections
[Fo > 4σ (Fo)]
7165
4442
4950
Number of parameters refined
Final R, Rw (obs. data)
GOOF
820
0.0364, 0.0871
1.007
390
0.0320, 0.0623
1.010
295
0.0442, 0.1092
0.993
(λmax : 20.920 cm-1, ε: 62450 mol-1cm-1) and 482 nm because of almost identical environment around nickel.
(λmax : 20.747 cm-1, ε : 65410 mol-1cm-1) for (1) and (2) However, reduction potential of the parent complex is
respectively are due to d-d transitions corresponding to much larger than those of the mixed ligand complexes
dz2---> dx2—y2 transitions and the other transitions in due to the greater π-accepting ability of the phosphines
the longer wavelength region are not prominent [7,11]. [18]. Following is the increasing trend of reduction
In complex (3), in addition to the charge transfer band at potentials (mV): -1501(2) < -1510(1) < -1512 (3) << -
~400 nm, a d-d band was observed at 450 nm (λmax : 1604 [Ni(pipdtc)2].
22.222 cm-1, ε: 582450 mol-1 cm-1) and is due to dz2--->
dx2—y2 transition. A very significant blue shift observed
in the d-d band for (3) compared to (1) and (2) is due
to the presence of strong field cyanide donor around
nickel. Presence of cyanide ligand increases the LFSE
and hence electronic transition to highly antibonding
dx2—y2 orbital is observed at lower wavelength.
3.3. Crystal structures
ORTEP diagram of complex (1) is shown in Fig. 3.
The molecule is a discrete mononuclear unit, which
has no significant intermolecular contacts. The planar
diamagnetic complex contains NiS2PN chromophore.
Two formula units are present in the unit cell.
The
Ni—S
bond
distances,
2.227(1)
and
3.2. Cyclic voltammetry
2.172(1) Å are significantly different due to the difference
All the complexes show metal centered reduction in trans influence exerted by phosphine and NCS
as reported earlier [7]. Figs. 1 and 2 show the one- anion. The thioureide C—N distance observed in
electron reductions corresponding to Ni(II)  Ni(I) for the compound is 1.289(3) Å, which is shorter than
two representative complexes. All the reductions have the distance observed in the parent [Ni(pipdtc)2]
been found to be irreversible. In all the reductions (1.327(5) Å) [14]. The Ni—P and Ni—N distances are
leading to the formation of Ni(I) complex, the reduced 2.209(1) and 1.865(2) Å respectively. The S—Ni—S
species is highly unstable undergoing decomposition bite angle is 78.58(4)° which is not quite different from
as is indicated by the complete irreversibility of the that observed in the parent dithiocarbamate.
processes. The observed process is an electrochemical The P—Ni—N angle (94.3(1)°) indicates the planar
reduction followed by chemical decomposition. The Ni(I) conformation of the complexes. The Ni—N—C angle
complexes produced by the electrochemical reduction (176.3(3)°) indicates small deviation from linearity
are of very short life time and decompose chemically and and is due to the steric effect of bulky phosphine
hence could not be identified in the reverse cycle. All the ligands. The bond parameters of the dithiocarbamate
phosphine complexes show similar reduction potentials moiety are found to be normal.
1201

Trans influence of triphenylphosphines and pseudohalogens
on Ni-S bonds: Synthesis, spectral and single crystal X-ray
structural studies on NiS2PN and NiS2PC chromophores
Figure 1. Cyclic voltammogram of [Ni(pipdtc)2].
Figure 2. Cyclic voltammogram of [Ni(pipdtc)(PPh3)(NCS)].
ORTEP of (2) is shown in Fig. 4. Two formula units group towards the metal atom. The Ni—P and Ni—N
are present in the unit cell. The mononuclear units show distances are 2.213(1) and 1.871(2) Å respectively. The
no significant intermolecular contacts. The diamagnetic S—Ni—S angle is found to be 78.67(3)°, which is similar
complex contains planar NiS2PN chromophore. The to the angle observed in the parent dithiocarbamate viz,
Ni—S bond distances, 2.182(1) and 2.206(1) Å are 79.4(1)°. The P—Ni—N angle indicates the near planar
significantly different, due to the trans influences exerted conformation of the complex. The Ni—N—C angle
by phosphine and NCS. PPh3 being a good π-acceptor (163.5(2)°) indicates deviation from linearity to a larger
has a greater trans influence and, hence the Ni—S bond extent compared to that observed in (1) due to the steric
trans to P is longer than the one trans to NCS anion. effect of the 4-methyl group.
Asymmetry in the Ni—S bonds leads to an increase
in Ni—S—C angle (86.64(7)°) and a contraction in is monomeric without any significant intermolecular
S—C—S angle (108.0(1)°). The C—N(thioureide) contacts. The complex contains planar NiS2PC
ORTEP of (3) is shown in Fig. 5. The complex
distance 1.303(2) Å, is significantly different from that chromophore. Two formula units are present in
of the parent [Ni(pipdtc)2] (1.327(5) Å) [14], indicating the unit cell. The Ni—S distances are 2.199(1)
the mesomeric drift of electron density from the S2CN and 2.206(1) Å and PPh3 shows a higher π-accepting
1202

K. Ramalingam et al.
Table 2. Selected bond distances (Å) and angles (°).
(1)
(2)
(3)
Ni(1)—S(2)
Ni(1)—S(3)
2.227(1)
2.172(1)
2. 209(1)
1.865(2)
1.723(2)
1.732(3)
1.289(3)
1.148(3)
1.618(3)
1.468(3)
1.820(2)
78.58(4)
93.9(1)
Ni(1)—S(2)
2.206(1)
2.182(1)
2.213(1)
1.871(2)
1.709(2)
1.730(2)
1.303(2)
1.150(2)
1.623(2)
1.473(3)
1.823(2)
78.67(3)
91.4(1)
Ni(1)—S(2)
Ni(1)—S(3)
2.206(1)
2.199(1)
2.203(1)
1.936(4)
1.725(4)
1.706(4)
1.313(5)
1.413(5)
1.160(6)
1.466(5)
1.822(2)
78.8(1)
89.9(1)
95.5(1)
95.7(1)
109.2(2)
125.0(3)
125.8(3)
123.2(3)
174.1(2)
-
Ni(1)—S(3)
Ni(1)—P(13)
Ni(1)—P(13)
Ni(1)—P(13)
Ni(1)—C(11)
Ni(1)—N(10)
Ni(1)—N10
S(2)—C(4)
S(2)—C(4)
S(2)—C(4)
S(3)—C(4)
S(3)—C(4)
S(3)—C(4)
C(4)—N(5)
C(4)—N(5)
C(4)—N(5)
N(10)—C(11)
N(10)—C(11)
C(11)—N(12)
N(5)—C(6)
C(11)—S(12)
C(11)—S(12)
N(5)—C(35)
N(5)—C(43)
N(5)—C(10)
P(13)—C(14)
P(13)—C(14)
P(13)—C(14)
S(2)—Ni(1)—S(3)
S(2)—Ni(1)—N(10)
N(10)—Ni(1)—P(13)
S(3)—Ni(1)—P(13)
S(2)—C(4)—S(3)
S(2)—C(4)—N(5)
S(3)—C(4)—N(5)
C(4)—N(5)—C(35)
Ni(1)—N(10)—C(11)
N(10)—C(11)—(S12)
S(2)—Ni(1)—S(3)
S(2)—Ni(1)—N(10)
N(10)—Ni(1)—P(13)
S(3)—Ni(1)—P(13)
S(2)—(C4)—S(3)
S(2)—C(4)—N(5)
S(3)—C(4)—N(5)
C(4)—N(5)—C(34)
Ni(1)—N(10)—C(11)
N(10)—C(11)—S(12)
S(2)—Ni(1)—S(3)
S(2)—Ni(1)—C(11)
C(11)—Ni(1)—P(13)
S(2)—Ni(1)—P(13)
S(2)—C(4)—S(3)
S(2)—C(4)—N(5)
S(3)—C(4)—N(5)
C(4)—N(5)—C(6)
Ni(1)—C(11)—N(12)
-
94.3(1)
93.8(1)
93.32(4)
107.5(1)
127.0(2)
125.5(2)
122.5(2)
176.3(3)
178.9(3)
96.07(3)
108.0(1)
126.4(1)
125.6(1)
122.2(2)
163.5(2)
178.9(2)
ability in the present case than the CN anion. The acetonitrilewhichshowedextensivedisorder(Hydrogens
thioureide C—N distance is 1.313(5) Å, which is shorter associated with the solvent molecule could not be
than the distance observed in its parent, 1.327(5) Å [14]. located). Important parameters of related compounds
The observed reduction in bond length is due to the are compared in Table 3.
mesomeric drift of electrons from the dithiocarbamate
moiety towards nickel atom. The Ni—P and Ni—C 3.4. Bond valence sum (BVS) analysis
distances are 2.203(2) Å and 1.936(4) Å, respectively. Bond valence sum (BVS) analysis has been used to
The S—Ni—S bite angle is 78.8 (1)°, which is similar determinetheoxidationstateofmetalionsinsolidsbased
to that observed in the parent dithiocarbamate. The on crystallographically determined M—L bond distances
P—Ni—C angle (95.5(1)°) indicates the near planar [19-21]. Calculation of BVS involves the relationship for
geometry of the complex. The Ni—C—N angle is the valence vij of a bond between two atoms i and j as
174.1(2)°, which indicates considerable deviation from vij = exp [(ro–r)/B], where ‘r’ is the crystallographically
linearity. The complex crystallizes with a molecule of determined bond length, ‘B’ is taken to be a universal
1203

Trans influence of triphenylphosphines and pseudohalogens
on Ni-S bonds: Synthesis, spectral and single crystal X-ray
structural studies on NiS2PN and NiS2PC chromophores
Figure 3. ORTEP of [Ni(pipdtc)(4-MP)(NCS)] (1) (Hydrogens are excluded; Ellipses are of 50% probability).
Figure 4. ORTEP of [Ni(pipdtc)(PPh3)(NCS)] (2) (Hydrogens are excluded; Ellipses are of 50% probability).
1204

K. Ramalingam et al.
Figure 5. ORTEP of [Ni(pipdtc)(PPh3)(CN)] (3) (Hydrogens are excluded; Ellipses are of 50% probability).
Table 3. Comparison of bond distances (Å) and angles (°).
Ni—N/
P—Ni—N/
P—Ni—C
Compound
Ni—S(1) Ni—S(2) Ni—P(1) Ni—P(2)
C—N
S—Ni—S
Ref.
Ni—C
[Ni(pipdtc)2]
2.207(1)
2.192(1)
2.216(4)
2.217(2)
2.196(1)
2.225(1)
2.206(4)
2.213(2)
2.172(1)
2.182(1)
2.199(1)
-
-
1.327(5)
1.284(5)
1.322(6)
1.272(10)
-
-
-
-
79.4(0)
78.2(1)
-
[14]
[21]
[Ni(pipdtc)(PPh3)2]+
[Ni(pipdtc)(1,3-dppp)]+
[Ni(pipdtc)(1,4-dppb)]+
2.201(1)
2.177(4)
2.209(2)
2.209(1)
2.213(1)
2.203(1)
2.229(1)
-
2.179(4)
79.2(1)
-
[22]
2.197(2)
78.34(9)
78.58(4)
78.67(3)
78.82(4)
-
[23]
[Ni(pipdtc)(4-MP)(NCS)] 2.227(1)*
-
-
-
1.289(3) 1.865(2)
1.303(3) 1.871(2)
1.313(5) 1.936(4)
94.3(1)
93.8(1)
95.5(1)
This work
This work
This work
[Ni(pipdtc)(PPh3)(NCS)]
[Ni(pipdtc)(PPh3)(CN)]
2.206(1)*
2.206(1)*
*Ni—S bond trans to Ni—P
Table 4. Values of ro used to calculate Bond Valence Sums.
values used in the present calculation and the values
of BVS calculated are given in Table 5. BVS calculated
by the use of ro obtained by OK/B method [19,20] for
divalent nickel complexes always resulted in a higher Vi,
i.e., a higher value than the formal oxidation state of +2.
For many of the dithiocarbamate complexes of nickel
(II), the bond valence sums exceeded 2.8. To overcome
the discrepancy, ro values have been re-determined for
some model complexes of transition metals from our
data [22-25]. BVS values obtained for the complexes
with the re-determined ro resulted in values closer to 2
confirming the oxidation state of nickel.
a)
Bond
ro/Å
ro/Å
Ni—S
Ni—N
Ni—P
Ni—C
2.059
1.743
2.128
1.818
1.937b)
1.647b)
1.884c)
1.604c)
a)[19,20] b) [21] c)r for Ni-C and Ni-P are reported from a fit of experimental
bond distances foor twenty complexes with divalent nickel as the central
metal [23-25]
The neutral isothiocyanato complexes have higher
BVS than the ionic phosphine complexes due to
variations in the metal – ligand bond distances and are
comparable to the BVS of parent bisdithiocarbamate.
The cationic complexes have relatively lower values as
constantequalto0.37androistheempiricallydetermined
bond valence parameter. The sum of the individual
values of vij for the j bond around a central metal gives
the BVS, Σ vij = Vi, which is generally close to the formal
oxidation state of the metal [19,20]. Table 4 lists the ro
1205

Trans influence of triphenylphosphines and pseudohalogens
on Ni-S bonds: Synthesis, spectral and single crystal X-ray
structural studies on NiS2PN and NiS2PC chromophores
Table 5. Bond Valence Sums (BVS) for divalent nickel complexes.
a marginally significant higher trans influence compared
to NCS-. The thioureide C—N distances in the mixed
ligand complexes are relatively very short compared
to the parent compound due to the mesomeric drift
of electron density towards the metal. The Ni—N—C
angle (163.5(2)°) observed in (2) indicates deviation
from linearity to a larger extent compared to that
observed in (1) (176.3(3)°) due to the steric effect
of the 4-methyl group However, the presence
of π-acids, PPh3 and 4-MP alleviate the electron
density on the nickel atom in solution and, hence
the reduction potentials for the mixed ligand
complexes are much less compared to the parent NiS4
chromophore.
Compound
BVSa) BVSb)
Ref.
[Ni(pipdtc)2]
3.005
2.919
3.073
2.944
2.892
2.885
2.896
1.957
1.779
1.857
1.763
1.949
1.948
1.803
[14]
[21]
[Ni(pipdtc)(PPh3)2]+
[Ni(pipdtc)(1,3-dppp)]+
[Ni(pipdtc)(1,4-dppb)]+
[Ni(pipdtc)(4-MP)(NCS)]
[Ni(pipdtc)(PPh3)(NCS)]
[Ni(pipdtc)(PPh3)(CN)]
[22]
[23]
This work
This work
This work
a) use of ro reported in the literature [19,20]
b) use of ro re-determined [23-25]
quoted from the literature. The bond valence parameters
reported for the present complexes clearly confirm the
formal oxidation state of nickel to be +2.
Supplementary material
CCDC 183258 (for 1), 238328 (for 2) and 210917
(for 3) contain supplementary crystallographic data
for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.
html (or from the Cambridge Crystallographic
4. Conclusions
The Ni—S distances in the complexes (1), (2) and (3) are Data Centre, 12, Union Road, Cambridge, CB2 1EZ, UK;
distinctly different and the observed asymmetry is due fax: +44 1223 336033; or deposit@ccdc.cam.ac.uk).
to differences in trans influences exerted by phosphine,
NCS- and CN-. Ni—S bond distances trans to PPh3/4-
MP are observed to be in the following order: (1) > (2) ~ Acknowledgement
(3). Ni—S bond distances trans to NCS/CN follow: (3) >
(2) > (1). The trans influence in divalent nickel complexes This work was supported by the Council of Scientific and
is clearly established by the observation. Particularly, Industrial Research, New Delhi, India for the financial
4-MP shows a highly significant trans influence than support as a SRF (NET). One of the authors (RTK) is
triphenylphosphine on Ni-S bond. Similarly, CN- exerts gratefully acknowledged.
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