Synthesis, crystal structures and spectral studies of square planar nickel(II) complexes containing an ONS donor Schiff base and triphenylphosphine

Article abstract of DOI:10.1016/j.poly.2009.04.021

Five mononuclear nickel(II) complexes, viz. [Ni(L1)(PPh₃)] (1), [Ni(L2)(PPh₃)] (2), [Ni(L3)(PPh₃)] (3), [Ni(L4)(PPh₃)] (4) and [Ni(L5)(PPh₃)] (5) (where L1, L2, L3, L4 and L5 are dianions of N-(2-mercaptophenyl)salicylideneimine, 5-methyl-N-(2-mercaptophenyl)salicylideneimine, 5-chloro-N-(2-mercaptophenyl)salicylideneimine, 5-bromo-N-(2-mercaptophenyl)salicylideneimine and N-(2-mercaptophenyl)naphthylideneimine, respectively), have been synthesized and characterized by means of elemental analysis, electronic, IR, ¹H, ¹³C and ³¹P NMR spectroscopy. Single crystal X-ray analysis of two of the complexes (1 and 5) has revealed the presence of a square planar coordination geometry (ONSP) about nickel. The crystal structures of the complexes are stabilized by intermolecular π-π stacking between the ligands (L) and by various C-H···π interactions.

Full text of DOI:10.1016/j.poly.2009.04.021

Polyhedron 28 (2009) 2157–2164
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, crystal structures and spectral studies of square planar nickel(II)
complexes containing an ONS donor Schiff base and triphenylphosphine
M. Muthu Tamizh a, Kurt Mereiter b, Karl Kirchner c, B. Ramachandra Bhat d, R. Karvembu a,
*
a Department of Chemistry, National Institute of Technology, Tanjore Road, Tiruchirappalli 620 015, Tamil Nadu, India
b Institute of Chemical Technologies and Analytics, Vienna University of Technology, A-1060 Vienna, Austria
c Institute of Applied Synthetic Chemistry, Vienna University of Technology, A-1060 Vienna, Austria
d Department of Chemistry, National Institute of Technology, Surathkal 575 025, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Five mononuclear nickel(II) complexes, viz. [Ni(L1)(PPh3)] (1), [Ni(L2)(PPh3)] (2), [Ni(L3)(PPh3)] (3),
[Ni(L4)(PPh3)] (4) and [Ni(L5)(PPh3)] (5) (where L1, L2, L3, L4 and L5 are dianions of N-(2-mercaptophenyl)
salicylideneimine, 5-methyl-N-(2-mercaptophenyl)salicylideneimine, 5-chloro-N-(2-mercaptophenyl)
salicylideneimine, 5-bromo-N-(2-mercaptophenyl)salicylideneimine and N-(2-mercaptophenyl)naphthy-
lideneimine, respectively), have been synthesized and characterized by means of elemental analysis, elec-
tronic, IR, 1H, 13C and 31P NMR spectroscopy. Single crystal X-ray analysis of two of the complexes (1 and 5)
has revealed the presence of a square planar coordination geometry (ONSP) about nickel. The crystal struc-
Received 13 May 2008
Accepted 10 April 2009
Available online 24 April 2009
Keywords:
Schiff base ligand
Triphenylphosphine
Ni(II) complexes
Spectral studies
Crystal structures
tures of the complexes are stabilized by intermolecular
ious C–HÁÁÁ interactions.
p
–
p
stacking between the ligands (L) and by var-
p
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
nyl)naphthylideneimine with Ni(II). Here, we report square planar
nickel(II) complexes of O,N,S donor ligands and triphenylphos-
phine. These complexes were characterized by IR, electronic and
NMR spectral data. The structures of two complexes have been
determined by single crystal X-ray crystallography. The general
structures of the ONS Schiff base ligands used in this study are de-
picted in Fig. 1.
The synthesis of geometrically distorted nickel(II) complexes
with mixed N and S donor sets is the research interest of many
groups [1]. Nickel is present in the active sites of several important
classes of metalloproteins, such as 2-mercaptoethanol-inhibited
urease and Ni/Fe hydrogenases [2]. The nickel coordination sphere
in both of these metalloenzyme systems contains N and S donor
sets. These features led to increased interest in the synthesis of
nickel(II) complexes with mixed N,S donating chelates as structural
and spectroscopic models of the active sites. There are many re-
ports available for nickel(II) complexes with N,S donor ligands
[3], but nickel(II) complexes containing N,S donor ligands as well
as triphenylphosphine are very rare [4]. Complexes of this kind
are interesting in terms of both models of the active sites and
homogeneous catalysis.
In addition, N-(2-mercaptophenyl)salicylideneimine exhibits
different kinds of coordination modes with different metal ions.
It behaves as a bifunctional tridentate ligand with Tc(V), Re(V),
Ru(II) and Ru(III) [5–7]. The same ligand shows monofunctional tri-
dentate coordination with Co(II), Cu(II) and Zn(II) [8] and mono-
functional bidentate coordination with Ru(I) [9]. Hence, we
intend to investigate the coordination behaviour of N-(2-mercap-
tophenyl)salicylideneimine, its derivatives and N-(2-mercaptophe-
2. Experimental
2.1. Materials
All the chemicals used were of analytical grade. Solvents were
purified and dried according to standard procedures [10].
NiCl2Á6H2O was purchased from Qualigens Fine Chemicals and
was used without further purification. The starting complex
[NiCl2(PPh3)2] was prepared by the reaction between NiCl2Á6H2O
and triphenylphosphine in glacial acetic acid [11]. The Schiff base
ligands were prepared by the condensation between salicylalde-
hyde, its derivatives or 2-hydroxy-1-naphthaldehyde and o-amino-
thiophenol in ethanol [5,12].
2.2. Physical measurements
Electronic spectra were measured on a Perkin Elmer EZ 301 UV–
Vis double beam spectrophotometer for CH3CN solutions of the
complexes in the 200–800 nm range. FT-IR spectra were recorded
* Corresponding author. Tel.: +91 422 2501801; fax: +91 431 2503632.
E-mail address: kar@nitt.edu (R. Karvembu).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.04.021

2158
M. Muthu Tamizh et al. / Polyhedron 28 (2009) 2157–2164
2.4. Synthesis of Ni(II) complexes
R
Ligand
H2L1
H2L2
H2L3
H2L4
HO
N
R
H
All the complexes were prepared by stirring an ethanolic solu-
tion of [NiCl2(PPh3)2] with dichloromethane solutions of the li-
gands in a 1:1 molar ratio for 2 h at 25–27 °C. The resulting dark
brown solutions were concentrated to approximately 3 cm3 and
cooled. Hexane (20 cm3) was then added, whereupon the product
complex separated. The brown coloured complex was filtered,
washed with ethanol and then with hexane, and dried in vacuo.
The formation of complex was checked by TLC.
HS
CH3
Cl
Br
[Ni(L1)(PPh3)] (1) is prepared from [NiCl2(PPh3)2] (0.5 g;
0.764 mmol) and H2L1 (0.175 g; 0.764 mmol). Yield: 59%. AnalC. alc.
HO
N
Table 1
Ligand
H2L5
Infrared spectral data (cmÀ1) for the ligands and their Ni(II) complexes.
HS
Compound
m(C@N)
m(C–O)
m(C–S)
m(Ni–O)
m(Ni–N) Bands due to PPh3
H2L1
H2L2
H2L3
H2L4
H2L5
(1)
(2)
(3)
(4)
(5)
1614
1622
1621
1612
1610
1607
1615
1619
1603
1598
1316
1323
1321
1317
1304
1334
1341
1325
1326
1321
754
756
753
757
757
746
744
743
752
750
Fig. 1. General structures of the ligands.
528
532
527
529
529
457
455
455
459
456
1433, 1095, 691
1435, 1096, 693
1434, 1093, 695
1437, 1098, 694
1435, 1097, 695
on a Perkin Elmer Spectrum One FT-IR spectrometer as KBr pellets
in the frequency range 400–4000 cmÀ1. The C, H, N and S contents
were determined by a Thermoflash EA1112 series elemental ana-
lyzer. 1H, 13C, HSQC and HMBC NMR spectra were recorded in a
Bruker AMX 400 instrument using TMS as the internal standard.
31P NMR spectra were recorded in a Bruker AMX 400 instrument
in CDCl3 with H3PO4 as a reference. Melting points were deter-
mined with a Khora digital melting point apparatus.
Table 2
1H, 13C and 31P NMR spectral data of the Ni(II) complexes.
Complex 1H (ppm)
13C (ppm)
31P
(ppm)
2.3. X-ray crystallography
(1)
(2)
(3)
(4)
(5)
6.4–8.0 (m, 23H, aromatic),
8.9 (d, J = 10.36 Hz, 1H,
–CH@N–)
163.98, 154.51, 149.82,
143.98, 143.85, 134.84,
134.72, 133.98, 133.00,
130.59, 130.57, 129.43,
129.00, 128.62, 128.60,
128.21, 128.11, 126.70,
121.88, 121.63, 119.30,
115.44, 114.84
22.3
22.3
22.4
22.5
25.2
Single crystals of 1 and 5 for X-ray diffraction studies were
grown at room temperature from a dichloromethane solution by
the diffusion of diethyl ether vapour. Diffraction data were col-
lected on a Bruker SMART APEX CCD diffractometer using graphite
monochromated Mo Ka radiation (k = 0.71073 Å). The structures
were solved by direct methods (SHELXS-97) [13] and refined by
full-matrix least squares fitting based on F2 using the program
SHELXL-97 [14]. All non-hydrogen atoms were refined with aniso-
tropic displacement parameters. All H atoms were located by dif-
ference Fourier syntheses and were then included in the
refinement with idealized geometry riding on the atoms to which
they were bonded.
2.3 (s, 3H, –CH3), 6.3–8.0 (m, 162.44, 154.25, 149.99,
22H, aromatic), 8.8 (d,
J = 9.36 Hz, 1H, –CH@N–)
144.46, 144.32, 135.95,
134.86, 134,72, 132.73,
130.55, 130.42, 129.69,
129.08, 128.63, 128.20,
128.07, 128.02, 126.52,
124.23, 121.83, 121.35,
118.84, 114.76, 20.23
6.3–8.0 (m, 22H, aromatic),
8.8 (d, J = 9.03 Hz, 1H,
–CH@N–)
162.53, 153.46, 149.43,
144.48, 144.33, 134.79,
134.66, 133.94, 131.84,
130.70, 130,67, 129.36,
128.74, 128.66, 128.28,
128.14, 127.06, 123.07,
122.03, 119.90, 119.54,
114.95
6.3–8.0 (m, 22H, aromatic),
8.8 (d, J = 9.34 Hz, 1H,
–CH@N–)
162.83, 153.39, 149.91,
144.42, 144.24, 136.46,
135.06, 134.79, 134.66,
130.72, 130.67, 129.35,
128.73, 128.66, 128.29,
128.16, 127.09, 123.50,
122.05, 120.83, 114.97,
106.28
6.3–8.1 (m, 25H, aromatic),
8.8 (d, J = 10.27 Hz,1H,
–CH@N–)
164.93, 151.12, 148.32,
143.23, 142.96, 134.84,
134.63, 134.19, 130.64,
130.60, 129.70, 129.08,
128.80, 128.32, 128.10,
127.58, 127.06, 126.03,
124.24, 122.77, 121.98,
118.94, 114.85, 110.29
Fig. 2. Electronic spectra of the nickel(II) complexes.

M. Muthu Tamizh et al. / Polyhedron 28 (2009) 2157–2164
2159
for C31H24NNiOPS: C, 67.90; H, 4.41; N, 2.55; S, 5.85. Found: C,
67.02; H, 3.96; N, 2.41; S, 6.11%. kmax ) CH3CN: 213(42900),
249(35135), 264(35496),
422(9885) nm(dm3 molÀ1 cmÀ1).
253(40015),
Decomposition temperature 246 °C.
[Ni(L4)(PPh3)] (4) is prepared from [NiCl2(PPh3)2] (0.5 g;
0.764 mmol) and H2L4 (0.25 g; 0.764 mmol). Yield: 40%. Anal.Calc.
for C31H23BrNNiOPS: C, 59.37; H, 2.23; N, 2.55; S, 5.11. Found: C,
267(39532),
429(10094) nm(dm3 molÀ1 cmÀ1).
(e
Decomposition temperature 230 °C.
[Ni(L2)(PPh3)] (2) is prepared from [NiCl2(PPh3)2] (0.25 g;
0.382 mmol) and H2L2 (0.093 g; 0.382 mmol). Yield: 67%. AnalC. alc.
for C32H26NNiOPS: C, 68.35; H, 4.66; N, 2.49; S, 5.70. Found: C,
59.18; H, 2.45; N, 2.27; S, 5.71%. kmax
253(40509), 267(40334),
(e) CH3CN: 212(45269),
428(11001) nm(dm3 molÀ1 cmÀ1).
67.99; H, 4.23; N, 2.80; S, 6.00%. kmax
253(43880), 267(45735),
Decomposition temperature 234 °C.
[Ni(L3)(PPh3)] (3) is prepared from [NiCl2(PPh3)2] (0.5 g;
0.764 mmol) and H2L3 (0.202 g; 0.764 mmol). Yield: 58%. AnalC. alc.
for C31H23ClNNiOPS: C, 63.90; H, 3.98; N, 2.40; S, 5.32. Found: C,
(
e
) CH3CN: 216(56603),
Decomposition temperature 239 °C.
431(11252) nm(dm3 molÀ1 cmÀ1).
[Ni(L5)(PPh3)] (5) is prepared from [NiCl2(PPh3)2] (0.5 g;
0.764 mmol) and H2L5 (0.214 g; 0.764 mmol). Yield: 57%. Anal. Calc.
for C35H26NNiOPS: C, 70.26; H, 4.38; N, 2.34; S, 5.36. Found: C,
69.66; H, 3.85; N, 2.18; S, 6.53%. kmax(e) CH3CN: 199(46749),
249(29007), 276(28964), 328(7516), 438(8550), 468(5901) nm
63.34; H, 3.52; N, 2.56; S, 5.85%. kmax
(e
) CH3CN: 216(45411),
(dm3 molÀ1 cmÀ1). Decomposition temperature 245 °C.
Fig. 3. 1H NMR spectrum of [Ni(L1)(PPh3)].
Fig. 4. HSQC spectrum of [Ni(L1)(PPh3)].

2160
M. Muthu Tamizh et al. / Polyhedron 28 (2009) 2157–2164
Fig. 5. HMBC spectrum of [Ni(L1)(PPh3)].
Fig. 6. 31P NMR spectra of the nickel(II) complexes.

M. Muthu Tamizh et al. / Polyhedron 28 (2009) 2157–2164
2161
Table 3
Crystal data, data collection and structure refinement parameters for (1) and (5).
3.2. IR spectra
Selected IR bands of the ligands and complexes are listed in
Table 1. The spectra of the ligands exhibit a strong band around
Parameters
(1)
(5)
Empirical formula
Formula weight
Colour
Habit
Crystal dimensions
(mm)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C31H24NNiOPS
548.25
dark brown
block
C35H26NNiOPS
598.31
dark brown
block
1610–1622 cmÀ1, which is assigned to a
m(C@N) vibration. As a
result of coordination, this band shifts to a lower wavenumber
by ca. 10 cmÀ1 in the complexes [4,16]. The band in the region
0.52 Â 0.42 Â 0.35
0.59 Â 0.55 Â 0.48
Table 4
triclinic
monoclinic
P21/c
13.1734(4)
17.2572(6)
12.6594(4)
90
130.720(1)
90
2795.82(16)
4
Selected bond lengths (Å) and angles (°).
ꢀ
P1
8.9703(4)
9.9644(4)
14.3335(6)
99.836(1)
94.904(1)
97.785(1)
1242.95(9)
2
(1)
(5)
Ni(1)–O(1)
Ni(1)–N(1)
Ni(1)–S(1)
Ni(1)–P(1)
S(1)–C(9)
P(1)–C(20)
P(1)–C(26)
P(1)–C(14)
O(1)–C(2)
N(1)–C(7)
N(1)–C(8)
C(1)–C(2)
C(8)–C(9)
C(1)–C(7)
1.8496(9)
1.9096(10)
2.1359(3)
Ni(1)–O(1)
Ni(1)–N(1)
Ni(1)–S(1)
Ni(1)–P(1)
S(1)–C(12)
P(1)–C(24)
P(1)–C(30)
P(1)–C(18)
O(1)–C(2)
N(1)–C(11)
N(1)–C(13)
C(1)–C(2)
1.8448(8)
1.8956(8)
2.1369(3)
2.1894(3)
1.7499(10)
1.8202(10)
1.8206(10)
1.8228(10)
1.2968(12)
1.3137(12)
1.4247(13)
1.4134(14)
1.4012(13)
1.4169(14)
a
(°)
b (°)
2.2164(3)
c
(°)
1.7512(12)
1.8196(12)
1.8211(11)
1.8214(11)
1.2995(14)
1.3054(15)
1.4268(14)
1.4088(16)
1.3960(16)
1.4216(17)
Volume (Å3)
Z
T (K)
100(2)
1.465
0.955
100(2)
1.421
0.856
DC (Mg/m3)
Absorption coefficient
(mmÀ1
)
F(0 0 0)
k (Å)
h Range (°)
Scan type
568
1240
Mo K
2.58–29.96
, u
a
(0.71073)
Mo K
2.33–29.99
, u
a (0.71073)
C(12)–C(13)
C(1)–C(11)
x
x
Index ranges
À12 6 h 6 12,
À13 6 k 6 13,
À20 6 l 6 20
18 052/7114
À18 6 h 6 17,
À20 6 k 6 24,
À17 6 l 6 17
29 095/8103
O(1)–Ni(1)–N(1)
O(1)–Ni(1)–S(1)
N(1)–Ni(1)–S(1)
O(1)–Ni(1)–P(1)
N(1)–Ni(1)–P(1)
S(1)–Ni(1)–P(1)
C(9)–S(1)–Ni(1)
C(20)–P(1)–C(26)
C(20)–P(1)–C(14)
C(26)–P(1)–C(14)
C(20)–P(1)–Ni(1)
C(26)–P(1)–Ni(1)
C(14)–P(1)–Ni(1)
C(2)–O(1)–Ni(1)
C(7)–N(1)–C(8)
C(7)–N(1)–Ni(1)
C(8)–N(1)–Ni(1)
N(1)–C(7)–C(1)
C(2)–C(1)–C(7)
C(8)–C(9)–S(1)
95.37(4)
173.98(3)
89.32(3)
O(1)–Ni(1)–N(1)
O(1)–Ni(1)–S(1)
N(1)–Ni(1)–S(1)
O(1)–Ni(1)–P(1)
N(1)–Ni(1)–P(1)
S(1)–Ni(1)–P(1)
C(12)–S(1)–Ni(1)
C(24)–P(1)–C(30)
C(24)–P(1)–C(18)
C(30)–P(1)–C(18)
C(24)–P(1)–Ni(1)
C(30)–P(1)–Ni(1)
C(18)–P(1)–Ni(1)
C(11)–N(1)–C(13)
C(11)–N(1)–Ni(1)
C(13)–N(1)–Ni(1)
C(2)–O(1)–Ni(1)
N(1)–C(11)–C(1)
C(2)–C(1)–C(11)
C(13)–C(12)–S(1)
94.34(3)
175.08(2)
90.15(3)
Reflections collected/
unique
Rint
82.58(3)
85.10(2)
174.75(3)
93.056(12)
98.64(4)
177.24(3)
90.311(11)
97.76(3)
0.0161
full-matrix
0.0185
full-matrix
Refinement method
least-squares on F2
Bruker SMART APEX CCD
multi-scan SADABS
0.0285/0.0750
least-squares on F2
Bruker SMART APEX CCD
multi-scan SADABS
0.0244/0.0651
104.11(5)
104.63(5)
105.55(5)
113.56(4)
107.01(4)
120.57(4)
128.25(8)
118.68(10)
122.90(8)
118.37(8)
127.12(11)
122.53(11)
118.42(8)
106.73(5)
104.79(4)
102.19(4)
105.04(3)
117.88(3)
119.02(3)
118.87(9)
123.28(7)
117.73(6)
127.63(7)
127.45(9)
120.51(9)
118.67(8)
Diffractometer
Absorption correction
Final R indices R1/wR2
[I > 2r(I)]
R1/wR2 (all data)
Goodness-of-fit (GOF)
on F2
0.0302/0.0762
1.051
0.0269/0.0665
1.038
D
qmax. (e ÅÀ3
)
0.70 and À0.26
0.42 and À0.33
Data/restraints/
parameters
7114/0/325
8103/117/361
3. Results and discussion
The reaction of equimolar ratios of the ligands (H2L) and
[NiCl2(PPh3)2] yielded the new complexes of the general formula
[Ni(L)(PPh3)] (L = dianionic Schiff base ligand) in moderate to good
yield. All the present complexes were brown in colour. They were
found to be soluble in CH2Cl2, CH3CN, C6H6, DMSO, DMF and
C2H5OH. The analytical data for these complexes are in good agree-
ment with the above molecular formula. In all the reactions, it has
been observed that the Schiff base behaves as a bifunctional triden-
tate ligand by substituting one of the triphenylphosphine ligands
and both the chloride ions from the starting complex.
3.1. Electronic spectra
The electronic spectra of the complexes (Fig. 2) 1, 2, 3 and 4 in
CH3CN showed four bands in the region 198–431 nm. The bands
appearing in the region 198–267 nm have been assigned to intral-
igand transitions. A less intense band in range 423–431 nm corre-
sponds to a forbidden d ? d transition. Complex 5 displayed six
bands in the 199–469 nm range. The extra bands are due to the
additional phenyl ring present in the ligand. Four bands in the re-
gion 199–323 nm are due to intraligand transitions and two bands
at 438 and 469 nm are due to forbidden d ? d transitions. The
same behaviour has been observed in the electronic spectra of
other similar square planar nickel(II) complexes [4,15].
Fig. 7. Molecular structure of complex 1 showing 50% displacement ellipsoids.

2162
M. Muthu Tamizh et al. / Polyhedron 28 (2009) 2157–2164
to the azomethine proton (–C@N–) [20]. Complex 3 exhibits a sin-
glet at 2.3 ppm, corresponding to methyl protons. The absence of a
resonance due to phenolic and thiolato hydrogen atoms indicates
the deprotonation of these groups and the Schiff bases behave as
dianionic ligands. The 1H NMR spectrum of 1 is depicted in
Fig. 3. In the 13C NMR spectra of all the complexes, azomethine car-
bon resonances are observed in the 151.12–154.49 ppm range. The
resonances for C–S, C–N, C–O and C–P are observed in the regions
129.00–129.69, 149.32–149.99, 162.44–164.93 and 142.96–
144.48 ppm, respectively [21,22]. The 13C NMR and DEPT 135 spec-
tra of 1 revealed the presence of seven different carbons (119.30,
129.00, 129.46, 143.85, 143.98, 149.82 and 163.98 ppm). This indi-
cates that the three quaternary carbons arising from triphenyl-
phosphine aromatic units are in different magnetic
environments. The HSQC correlation spectrum of 1 (Fig. 4) estab-
lishes the connection between the imine proton (dH = 8.89, d,
J = 10.36 Hz, 1H) and C-7 (dC = 154.51). The interaction of the imine
proton (dH = 8.89, d, J = 10.36 Hz, 1H) with three quaternary car-
bons viz. C-1 (dC = 119.30), C-2 (dC = 163.98) and C-8 (dC = 149.82)
and the methine carbon C-6 (dC = 134.00) has been understood
from the HMBC correlation spectrum (Fig. 5). The 31P NMR spectra
of all the complexes exhibit a singlet around 22.3–25.2 ppm, sug-
gesting the presence of one coordinated triphenylphosphine ligand
in these nickel(II) complexes [23]. The 31P NMR spectra of all the
complexes are given in Fig. 6.
Fig. 8. Molecular structure of complex 5 showing 50% displacement ellipsoids.
1304–1323 cmÀ1, which is assigned to phenolic
m(C–O) in the free
ligand, is shifted to a higher wavenumber in the complexes, sug-
gesting the coordination of the phenolic oxygen atom to the nickel
ion [4,16]. A weak band observed in the region 753–757 cmÀ1, cor-
3.4. X-ray crystallography
responding to m(C–S) in the ligands, shifts to a lower wavenumber
The compounds 1 and 5 were structurally determined by X-ray
crystallography. The crystallographic and measurement data are
shown in Table 3 and representative bond lengths and bond angles
are listed in Table 4. Figs. 7 and 8 present thermal ellipsoid repre-
sentations of complexes 1 and 5, respectively. In both the com-
plexes, the nickel(II) atom is four coordinated in a square planar
geometry by the Schiff base and triphenylphosphine ligands. The
Schiff base acts as a tridentate ligand through the thiolato sulfur
atom, the imine N and the phenolic O atom. Two units of
[Ni(L1)(PPh3)] and four units of [Ni(L5)(PPh3)] are present in their
respective unit cells. As expected for four coordinate d8 metal com-
plexes, the structure of 1 adopts a nearly ideal square planar geom-
etry with O–Ni–S and N–Ni–P bond angles of 173.98(3) and
174.75(3)°, respectively [24]. The other angles around the nickel(II)
(743–752 cmÀ1) which supports sulfur coordination with the nick-
el centre [17]. The bands around 530 and 460 cmÀ1 in all the com-
plexes are assigned to
m(Ni–O) and m(Ni–N), respectively [18].
Bands due to triphenylphosphine also appear in the expected re-
gion [19].
3.3. NMR spectra
1H, 13C and 31P NMR spectral data of the complexes are given in
Table 2. All the nickel(II) complexes exhibit a multiplet around 6.3–
8.1 ppm, which has been assigned to the protons of the phenyl
groups present in triphenylphosphine and the Schiff base ligand.
A doublet observed at 8.8 ppm in the complexes has been assigned
Fig. 9. Schematic drawing of the crystal packing of 1 showing the p–p stacking parallel to the a-axis. Hydrogen atoms are omitted.

M. Muthu Tamizh et al. / Polyhedron 28 (2009) 2157–2164
2163
Fig. 10. Schematic drawing of the crystal packing of 5 showing the p–p stacking between pairs of complexes via their naphthyl moieties. Hydrogen atoms are omitted.
atom deviate slightly from the ideal value (90°), ranging from
82.58(3) to 95.37(4)°. In structure 5, the O–Ni–S and N–Ni–P bond
angles are 175.08(2) and 177.24(3)°, respectively and other angles
around nickel(II) are in the range 85.10(2) to 94.34(3)°. The Ni–P,
Ni–O, Ni–N and Ni–S bond distances are in the usual range in both
complexes [4]. Disregarding triphenylphosphine, complex 1 is
essentially planar, showing a r.m.s. deviation of 0.030 Å of the
non-hydrogen atoms from a common least-squares plane, from
which the P atom deviates by 0.324(1) Å. Complex 5 is distinctly
more aplanar showing for the Ni(L5) moiety a r.m.s. deviation of
0.154 Å from planarity and a significant twist between the phenyl
and the naphthyl residues of L5 (interplanar angle 14.15(5)°).
These differences between [Ni(L1)(PPh3)] and [Ni(L5)(PPh3)] are
attributable to differences in crystal packing and intermolecular
interactions. The intermolecular interactions in [Ni(L1)(PPh3)] are
intermolecular
p–p stacking between the ligands (L) and by vari-
ous C–HÁÁÁ interactions.
p
Supplementary data
CCDC 663130 and 653443 contain the supplementary crystallo-
graphic data for 1 and 5. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
R.K. and B.R.B. are thankful to the Technical Education Quality
Improvement Program (TEQIP) for financial support under the
institution networking scheme. K.K. also thanks TEQIP, NITT, for
the award of a Visiting Professorship. R.K. and M.M. gratefully
acknowledge CSIR [01(2137)/07/EMR-II] for financial support. We
thank Dr. K. Shanmugasundaram and Mr. S. Ganesamoorthy, Syn-
gene International Pvt. Ltd., Bangalore for useful discussion regard-
ing 2D NMR.
characterized by comparatively weak
continuous chains along the a-axis (Fig. 9). In [Ni(L5)(PPh3)], there
are pairs of complexes stacked via their naphthyl moieties
(Fig. 10). The PPh3 moieties in both [Ni(L1)(PPh3)] and
[Ni(L5)(PPh3)] do not show stacking but contribute by various
C–HÁÁÁ interactions to the coherence of the structures.
p–p stacks of L1, forming
p–p
p–p
p
4. Conclusion
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IR and electronic spectroscopy. Structures of two complexes were
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