Platinum(II) complexes with bidentate iminopyridine ligands: Synthesis, spectral characterization, properties and structural analysis

Article abstract of DOI:10.1016/j.poly.2010.04.015

Four platinum(II) complexes, [PtCl₂L] (L = (4-fluorophenyl) pyridin-2-ylmethylene-amine, 1; (4-chlorophenyl)pyridin-2-ylmethyleneamine, 2; (4-bromophenyl)pyridin-2-ylmethyleneamine, 3 and (4-iodophenyl)pyridin-2- ylmethyleneamine, 4) have been synthesized and characterized by CHN analysis, IR and UV-Vis spectroscopy. The crystal structures of 1 and 2 were determined using single crystal X-ray diffraction. The coordination polyhedron about the platinum (II) center in the complexes is best described as distorted square planar. The complexes undergo stacking to form a zigzag Pt?Pt?Pt chain containing both short (3.57(7) ? in 1 and 3.62(8) ? in 2) and long (5.16(7) ? in 1 and 5.41(9) ? in 2) Pt?Pt separations through the crystal. The compounds absorb moderately in the visible region, owing to a charge-transfer-to-diimine electronic transition. The redox potentials are approximately insensitive to the substituents on the phenyl ring of the ligands.

Full text of DOI:10.1016/j.poly.2010.04.015

Polyhedron 29 (2010) 2190–2195
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Platinum(II) complexes with bidentate iminopyridine ligands: Synthesis,
spectral characterization, properties and structural analysis
b
b
Saeed Dehghanpour a, , Ali Mahmoudi , Soghra Rostami
*
a Department of Chemistry, Alzahra University, P.O. Box 1993891176, Tehran, Iran
b Department of Chemistry, Islamic Azad University, Karaj Branch, Karaj, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Four platinum(II) complexes, [PtCl2L] (L = (4-fluorophenyl)pyridin-2-ylmethylene-amine, 1; (4-chloro-
phenyl)pyridin-2-ylmethyleneamine, 2; (4-bromophenyl)pyridin-2-ylmethyleneamine, 3 and (4-iodo-
phenyl)pyridin-2-ylmethyleneamine, 4) have been synthesized and characterized by CHN analysis, IR
and UV–Vis spectroscopy. The crystal structures of 1 and 2 were determined using single crystal X-ray
diffraction. The coordination polyhedron about the platinum (II) center in the complexes is best described
as distorted square planar. The complexes undergo stacking to form a zigzag PtꢀꢀꢀPtꢀꢀꢀPt chain containing
both short (3.57(7) Å in 1 and 3.62(8) Å in 2) and long (5.16(7) Å in 1 and 5.41(9) Å in 2) PtꢀꢀꢀPt
separations through the crystal. The compounds absorb moderately in the visible region, owing to a
charge-transfer-to-diimine electronic transition. The redox potentials are approximately insensitive to
the substituents on the phenyl ring of the ligands.
Received 21 December 2009
Accepted 13 April 2010
Available online 28 April 2010
Keywords:
Platinum(II) complexes
Diimine ligands
Spectroscopy
Electrochemistry
Crystal structures
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
methods [19]. Samples of [PtCl2(CH3CN)2] were prepared as
described in the literature [20]. The ligands (4-fluorophenyl)
Platinum complexes with the diimine ligands have inspired
considerable research efforts. For example, such complexes have
found widespread use as optical materials, DNA intercalators and
solar cell dyes [1–5]. The interesting photochemical and photo-
physical properties of such compounds have also been thoroughly
investigated [6,7]. Factors such as steric, electronic and conforma-
tional interactions influence the spectroscopic properties of these
complexes and modify their redox potentials, which are important
in practical applications [8–10]. The majority of research in this
field has focused on the use of polypyridine derivatives such as
2,20-bipyridine, 1,10-phenanthroline as ligands [11–14]. However,
there is little data on complexes with unsymmetrical diimine li-
gands containing iminopyridine [15–18]. According to this view,
we describe the synthesis, properties and structural characteriza-
tion of Pt(II) complexes of the type [PtCl2L2] in which L is an
unsymmetrical bidentate iminopyridine ligand.
pyridin-2-ylmethylene-amine, A, (4-chlorophenyl)pyridin-2-ylm-
ethyleneamine, B, (4-bromophenyl)pyridin-2-ylmethyleneamine,
C, and (4-iodophenyl)pyridin-2-ylmethyleneamine, D) were pre-
pared according to reported procedures [21]. Elemental analyses
were performed using a Heraeus CHN-O-RAPID elemental ana-
lyzer. Infrared spectra were recorded on a Bruker Tensor 27 instru-
ment. Electronic absorption spectra were recorded on a JASCO V-
570 spectrophotometer; kmax (log e). NMR spectra were obtained
on a BRUKER AVANCE DRX500 (500 MHz) spectrometer. Proton
chemical shifts are reported in parts per million (ppm) relative to
an internal standard of Me4Si. All Pt chemical shifts are reported
in parts per million (ppm) relative to K2PtCl4. All voltammograms
were recorded using a three electrode system consisting of an
Ag/AgCl reference electrode, a platinum wire counter electrode
and an Au working electrode. A Metrohm multipurpose instrument
model 693 VA processor with 694A Va stand was used. In all elec-
trochemical experiments, the test solutions were purged with ar-
gon gas for at least 5 min.
2. Experimental
2.1. General
2.2. Syntheses
All chemicals used were reagent grade and were used as re-
ceived. Solvents used for the reactions were purified by literature
2.2.1. Synthesis of PtCl2(A), 1
Although complexes 1 and 2 have been synthesized before
[22,23], here we report a new method for their synthesis. A
125 ml Schlenk flask equipped with a magnetic stirring bar was
charged with PtCl2(CH3CN)2 (35.0 mg, 0.1 mmol) and 20 mg
* Corresponding author. Tel./fax: +98 21 88041344.
E-mail address: dehganpour_farasha@yahoo.com (S. Dehghanpour).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.04.015

S. Dehghanpour et al. / Polyhedron 29 (2010) 2190–2195
2191
(0.1 mmol) (4-fluorophenyl)pyridin-2-ylmethyleneamine, A and
flushed with nitrogen. Acetonitrile (20 ml) was added using a syr-
inge and the resulting solution was sealed under nitrogen, heated
to 50 °C, and stirred for 48 h to complete the transformation to
the desired product. The solid precipitating from the solution upon
cooling to ambient temperature was isolated by filtration and
washed with acetonitrile. The precipitate was dissolved in chloro-
form (4 ml). Blowing diethyl ether vapor into the solution gave or-
ange crystals, which were filtered off and washed with diethyl
by filtration and dried in vacuo. As the crystals slowly deteriorated
on standing, presumably due to loss of solvent, samples for micro-
analyses were dried in vacuo. Yield: 79%. IR (KBr/m
, cmꢁ1): 1580
(C=N). 1H NMR (DMSO-d6, ppm): 7.42–7.71 (m, 3H, ArH, amine
ring), 7.99 (t, 1H, JH1,2 = 5.7, JH2,3 = 6.5, H2), 8.22 (d, 1H, JH4,3 = 7.9,
H4), 8.44 (t, 1H, JH3,2 = 6.5, JH3,4 = 7.9, H3), 9.34 (s, 1H, Jpt–H = 44,
H5), 9.45 (d, 1H, JH2,1 = 5.7, Jpt–H = 31, H1). 195Pt NMR (DMSO-d6,
ppm): ꢁ2209. Anal. Calc. for C12H9Cl2FN2Pt: C, 27.34; H, 1.72; N,
5.31. Found: C, 27.38; H, 1.79; N, 5.26%.
ether and dried at reduced pressure. Yield: 81%. IR (KBr/m
, cmꢁ1):
1595 (C@N). 1H NMR (DMSO-d6, ppm): 7.30–7.54 (m, 3H, ArH,
amine ring), 7.98 (t, 1H, JH1,2 = 5.6, JH2,3 = 7.3, H2), 8.21 (d, 1H,
JH4,3 = 8.1, H4), 8.43 (t, 1H, JH3,2 = 7.3, JH3,4 = 8.1, H3), 9.33 (s, 1H,
Jpt–H = 47, H5), 9.46 (d, 1H, JH2,1 = 5.6, Jpt–H = 32, H1). 195Pt NMR
(DMSO-d6, ppm): ꢁ2212. Anal. Calc. for C12H9Cl2FN2Pt: C, 30.92;
H, 1.95; N, 6.01. Found: C, 30.85; H, 1.92; N, 6.09%.
2.2.4. Synthesis of PtCl2(D), 4
This complex was prepared by a procedure similar to that
for the synthesis of 1 using 30.8 mg (0.1 mmol) of (4-iodo-
phenyl)pyridin-2-ylmethyleneamine, D. Orange crystals were
collected by filtration and dried in vacuo. Yield: 79%. IR (KBr/
m
, cmꢁ1): 1575 (C@N). 1H NMR (DMSO-d6, ppm): 7.27–7.87
(m, 3H, ArH, amine ring), 7.98 (t, 1H, JH1,2 = 5.6, JH2,3 = 6.1,
H2), 8.22 (d, 1H, JH4,3 = 9.1, H4), 8.43 (t, 1H, JH3,2 = 6.1,
JH3,4 = 9.1, H3), 9.32 (s, 1H, Jpt–H = 46, H5), 9.46 (d, 1H,
JH2,1 = 5.6, Jpt–H = 33, H1). 195Pt NMR (DMSO-d6, ppm): ꢁ2206.
Anal. Calc. for C12H9Cl2FN2Pt: C, 25.11; H, 1.58; N, 4.88. Found:
C, 25.16; H, 1.62; N, 4.89%.
2.2.2. Synthesis of PtCl2(B), 2
This complex was prepared by a procedure similar to 1 using
21.7 mg (0.1 mmol) of (4-chlorophenyl)pyridin-2-ylmethylene-
amine, B. Orange crystals of 2 suitable for single crystal X-ray dif-
fraction were isolated directly from the solution after a few days.
As the crystals slowly deteriorated on standing, presumably due
to loss of solvent, samples for microanalyses were dried in vacuo.
2.3. X-ray analyses
Yield: 79%. IR (KBr/m
, cmꢁ1): 1586 (C@N). 1H NMR (DMSO-d6,
ppm): 7.36–7.54 (m, 3H, ArH, amine ring), 7.98 (t, 1H, JH1,2 = 5.7,
JH2,3 = 6.4, H2), 8.21 (d, 1H, JH4,3 = 9.1, H4), 8.44 (t, 1H, JH3,2 = 6.4,
JH3,4 = 9.1, H3), 9.32 (s, 1H, Jpt–H = 45, H5), 9.47 (d, 1H, JH2,1 = 5.7,
Jpt–H = 31, H1). 195Pt NMR (DMSO-d6, ppm): ꢁ2211. Anal. Calc. for
Data were collected on a Bruker-Nonius Kappa-CCD diffrac-
tometer using monochromated Mo K
using a combination of / scans and
a
radiation and measured
x
scans with offsets to fill
j
the Ewald sphere. The data was processed using the Denzo-SMN
package [24]. Absorption corrections were carried out using SOR-
TAV [25]. The structures were solved and refined using SHELXTL
V6.1 [26] for full-matrix least-squares refinement based on F2.
All H-atoms were included in calculated positions and allowed
to refine in a riding-motion approximation with Uiso tied to
the carrier atom. Crystallographic data for the compounds are gi-
ven in Table 1.
C
12H9Cl2FN2Pt: C, 29.86; H, 1.88; N, 5.80. Found: C, 29.92; H,
1.85; N, 5.74%.
2.2.3. Synthesis of PtCl2(C), 3
This complex was prepared by a procedure similar to that for
the synthesis of 1 using 26.1 mg (0.1 mmol) of (4-bromophe-
nyl)pyridin-2-ylmethyleneamine, C. Orange crystals were collected
Table 1
Crystal data and single crystal X-ray diffraction refinement details for compounds 1 and 2ꢀ1/4CH3CN.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C12H9Cl2FN2Pt
466.20
150(1)
0.71073
monoclinic
P2/n
7.5531(6)
C12.50H9.75Cl3N2.25Pt
492.92
150(2)
0.71073
monoclinic
C2/c
35.2284(15)
b (Å)
12.1563(10)
7.6261(4)
c (Å)
13.9331(7)
26.0259(9)
b (°)
101.466(5)
1253.77(16)
127.465(2)
5549.7(4)
V (A3)
Z
4
16
2.360
10.675
3672
Density (g cmꢁ3
)
2.470
11.610
864
l
(mmꢁ1
F(0 0 0)
Crystal size
)
0.17 ꢂ 0.07 ꢂ 0.03
0.08 ꢂ 0.04 ꢂ 0.03
Theta range for data collection
Index ranges
Reflections collected
2.86–24.99
2.77–25.00
ꢁ8 6 h 6 8, ꢁ14 6 k 6 14, ꢁ16 6 l 6 16
6907
ꢁ41 6 h 6 41, ꢁ9 6 k 6 9, ꢁ30 6 l 6 30
21,665
Independent reflections
Completeness to theta = 25.00°
Absorption correction
Max. and min. transmission
Refinement method
2186 [Rint = 0.0609]
98.9%
semi-empirical from equivalents
0.654 and 0.345
full-matrix least-squares on F2
2186/0/163
4862 [Rint = 0.1323]
99.7%
semi-empirical from equivalents
0.740 and 0.495
full-matrix least-squares on F2
4862/48/340
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.045
1.030
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0545, wR2 = 0.1417
R1 = 0.0669, wR2 = 0.1554
3.719 and ꢁ2.785
R1 = 0.0539, wR2 = 0.1070
R1 = 0.1150, wR2 = 0.1350
2.920 and ꢁ1.964
Largest differences in peak and hole (e Åꢁ3)

2192
S. Dehghanpour et al. / Polyhedron 29 (2010) 2190–2195
Table 2
UV–Vis spectral data and cyclic voltammetric data of the complexes.
Compound
kmax/nm, log
e
/Mꢁ1 cmꢁ1a
Reductionb
Epc1(ipc/ pa
Oxidationb
i
)
Epc2
Epa
1
2
3
4
423(2.64), 336(3.13), 266(3.79), 260(3.79)
425(2.38), 319(2.91), 267(3.25), 259(3.26)
423(2.68), 334(3.24), 283(3.46), 259(3.56)
424(2.72), 339(3.38), 283(3.56), 259(3.76)
ꢁ1.13(0.3)
ꢁ1.12(0.2)
ꢁ1.14(0.3)
ꢁ1.12(0.2)
ꢁ1.70
ꢁ1.75
ꢁ1.76
ꢁ1.74
0.67
0.65
0.64
0.68
a
Solvent: DMSO.
b
Solvent: CH3CN, scan rate = 0.1 V sꢁ1
.
[21]. The absorption spectra of all the complexes exhibit a broad
band close to 425 nm. This lowest energy feature in each case is
3. Results and discussion
*
the metal-to-ligand (PtII ? imine
p ) charge transfer (MLCT) tran-
3.1. Synthesis and spectral properties
sition. A slight red-shift of this band with an increase in the dipole
moment of the solvent can be noted (Table 3). A similar shift has
been reported for complexes of the type [Pt(NN)Cl2] [8,32,33].
Other higher energy bands are observed, which are combinations
The reaction of the ligands with [PtCl2(CH3CN)2] yields the com-
plexes [PtCl2(L)2]. These complexes are orange solids, which are
soluble in chloroform, methanol, ethanol, and acetone and are sta-
ble under ambient conditions. Although Kawakami et al. described
the synthesis of complex 1 with (C6H5CN)PtCl2 as the starting
material, there is no clear NMR data of the complex due to the
low intensity of the signals. However, using the M–Cl bands ob-
served in the infrared spectrum, a square planar geometry was
concluded for the complex (which is in accord with the X-ray anal-
ysis report in this paper) [22]. The synthesis of complex 1 was also
reported by Scale and co-workers. The precursor complex was
PtCl2(coe)2 and cytotoxic properties, 1H, 13C and 19F NMR data of
the complex have been reported [23].
*
of internal p–p transitions and higher energy MLCT transitions.
The redox behavior of the complexes in CH3CN solution was
examined by cyclic voltammetry. In general, these complexes
show two reduction waves at potentials ranging from ꢁ1.75 to
ꢁ1.12 V (Fig. 1). The first reduction wave is quasireversible and
the ratio of the anodic and cathodic peak currents, ipa/ipc, ap-
proaches 1 as the scan rate increases. The peak-to-peak separation
for the first reduction wave varies from 120 to 180 mV as the scan
rate is changed from 50 to 700 mV/s. The second reduction wave is
irreversible in acetonitrile, showing no anodic peak. The corre-
sponding anodic peak is not observed even under fast-scan-rate
conditions. This is probably due to an irreversible chemical reac-
tion (due to the instability of the reduction products) following
the electron-transfer process. A similar reduction wave is also ob-
served in structurally related complexes [34,35]. A similar differ-
ence between the first and the second reduction potential is
consistent with those found for similar complexes with the same
electrochemical process [8,32,34–36]. An irreversible oxidation is
observed in the anodic region for complexes 1–4 at about
+0.67 V, which can be assigned to platinum [8,32,34–36]. No sig-
nificant changes are observed with variation of the ligands in the
oxidation wave of the complexes.
Elemental analysis confirms the named stoichiometries of all
the complexes. The IR spectra in the 4000–400 cmꢁ1 range show
that the ligand is coordinated to the Pt(II) ions. The most striking
bands of the diimine ligands (m(C@N)) decrease in frequency when
they are part of the complexes [21,27].
The peak assignments for the 1H NMR spectra are presented in
the experimental section for each complex. These peaks are as-
signed based on the splitting of the resonance signals, spin cou-
pling constants, literature data and in accordance with the
molecular structure determined by the X-ray crystal structure
analysis. The 1H resonances of the coordinated ligands are ob-
served in complexes 1–4. Aside from the aromatic H-atoms, which
appear at 7.27–7.87 ppm, the imine protons appear as a singlet at
9.32–9.34 ppm. The downfield shift of the imine protons relative to
the free ligands can be attributed to the deshielding effect resulting
from the coordination of the metal by the ligands [9]. Platinum sat-
ellites are also observed for this resonance (JH–Pt ꢃ 45 Hz) upon
complexation of the ligand with the metal. Similar trends are also
observed for the ortho proton of the pyridine ring as the chemical
shift changes from d 9.45 to 9.47 ppm (JH–Pt ꢃ 32 Hz). The other
protons of the pyridine ring appear at 7.98–8.44 ppm and the
assignments are given in the experimental section. The 195Pt
NMR spectra of the platinum Schiff base complexes show signals
at ꢁ2212 ppm for 1, ꢁ2211 ppm for 2, ꢁ2209 ppm for 3 and
ꢁ2206 ppm for 4. The data is consistent with a platinum environ-
ment of two nitrogens and two chlorines [28–31].
3.2. Crystal structures
The crystallographic data for compounds 1 and 2 are summa-
rized in Table 1 and selected bond distances and angles are given
in Table 4.
The electronic spectra of the complexes were recorded in the
700–200 nm range. The spectral data is presented in Table 2. The
uncoordinated ligands are completely transparent above 335 nm
Table 3
Effect of solvents on the low-energy MLCT band of complexes 1–4.
CHCl3
CH3CN
DMF
DMSO
1
2
3
4
412
414
4.10
415
415
416
414
418
418
420
416
421
423
425
423
424
Fig. 1. Cyclic voltammograms of 1 in acetonitrile at 25 °C, [Bu4N]ClO4 supporting
electrolyte (0.1 M), scan rate = 0.10 V sꢁ1
.

S. Dehghanpour et al. / Polyhedron 29 (2010) 2190–2195
2193
Table 4
Selected bond lengths [Å] and bond angles [°] for 1 and 2ꢀ1/4CH3CN.
1
2 CH3CN
I
II
Pt(1)–N(1)
Pt(1)–N(2)
Pt(1)–Cl(1)
Pt(1)–Cl(2)
N(1)–Pt(1)–N(2)
N(1)–Pt(1)–Cl(1)
N(2)–Pt(1)–Cl(1)
N(1)–Pt(1)–Cl(2)
N(2)–Pt(1)–Cl(2)
Cl(1)–Pt(1)–Cl(2)
2.017(11)
2.027(10)
2.288(3)
2.299(3)
80.1(4)
Pt(1A)–N(1A)
Pt(1A)–N(2A)
Pt(1A)–Cl(2A)
Pt(1A)–Cl(1A)
N(1A)–Pt(1A)–N(2A)
N(1A)–Pt(1A)–Cl(2A)
N(2A)–Pt(1A)–Cl(2A)
N(1A)–Pt(1A)–Cl(1A)
N(2A)–Pt(1A)–Cl(1A)
Cl(2A)–Pt(1A)–Cl(1A)
2.007(11)
2.014(10)
2.285(3)
2.299(4)
79.5(4)
175.6(3)
97.1(3)
94.7(4)
Pt(1B)–N(1B)
Pt(1B)–N(2B)
Pt(1B)–Cl(1B)
Pt(1B)–Cl(2B)
N(1B)–Pt(1B)–N(2B)
N(1B)–Pt(1B)–Cl(1B)
N(2B)–Pt(1B)–Cl(1B)
N(1B)–Pt(1B)–Cl(2B)
N(2B)–Pt(1B)–Cl(2B)
Cl(1B)–Pt(1B)–Cl(2B)
2.030(10)
2.032(10)
2.289(4)
2.289(3)
80.7(4)
94.7(3)
93.5(3)
174.8(3)
175.6(3)
96.6(3)
174.2(3)
177.6(3)
98.0(3)
174.2(3)
88.67(13)
88.56(11)
87.75(13)
Fig. 2. Structure of 1 in the crystal, showing the atom-labelling scheme and thermal ellipsoids with 50% probability.
3.2.1. [Pt(A)Cl2] (1)
A view of complex 1, including the atom numbering scheme, is
illustrated in Fig. 2. The geometry around the d8 Pt center in 1 is a
distorted square plane, where the relatively small N(1)–Pt–N(2)
bond angle of 80.51(8)° is a result of chelating ligand steric con-
straints. The bond angles around the Pt atom are consistent with
a planar geometry, which sum to 359.96°. All of the Pt–N and Pt–
Cl bond lengths and angles are very similar to those previously re-
ported in related systems [14,15]. The relatively short C@N bond
length of 1.284(16) Å for C(6)–N(2), compared to the C(1)–N(1)
bond length of 1.329(17) Å and the C(5)–N(1) bond length of
1.369(18) Å in the pyridine ring, is consistent with a lack of imine
double-bond delocalization in 1 [15].
A mean plane analysis of the five atoms comprising the transi-
tion metal square plane reveals a maximum deviation from ideality
of 0.095(12) Å for N(1). In addition, a least-squares analysis of the
11 atoms, including those in the pyridine and the metal chelate
rings, finds a maximum deviation of only 0.2614(114) Å for C(4).
The aryl ring of the pyridinylimine ligand, containing C(7)–C(12),
is tilted out-of-plane with respect to the metal chelate plane, with
a calculated torsion angle of 42.64(6)° between the two planes.
Terminal phenyl rings which contain bulkier non-hydrogen sub-
stituents tend to adopt a nearly perpendicular position relative to
the metal chelation plane in structurally related compounds [37–
40]. The molecules stack in the a direction in a head to tail fashion
with two different PtꢀꢀꢀPt distances (Fig. 3). In this arrangement, the
short PtꢀꢀꢀPt distance is 3.57(7) Å. The second PtꢀꢀꢀPt distance is
much longer (5.16(7) Å) and the PtꢀꢀꢀPtꢀꢀꢀPt chain angle is
118.66(2)°. The platinum–platinum vector in 1 inclines by only
Fig. 3. Crystal packing of 1, the stacking occurs along the a-axis.

2194
S. Dehghanpour et al. / Polyhedron 29 (2010) 2190–2195
Fig. 4. Structure of 2ꢀ1/4CH3CN in the crystal, showing the atom-labelling scheme and thermal ellipsoids with 50% probability.
Table 5
Geometry of the pyridine, chelate and benzene ring in compounds 1 and 2.
1
2
A
B
Planes 1 (pyridine ring)
Planes 2 (chelate ring)
Planes 3 (benzene ring)
Dihedral angle (°) between planes 1 and 2
Dihedral angle (°) between planes 2 and 3
Dihedral angle (°) between planes 1 and 3
Torsion angle (°) N–C–C–N
N1–C1–C2–C3–C4–C5
N1–C5–C6–N2
C7–C8–C9–C10–C11–C12
2.596(5)
44.262(4)
42.644(5)
N1a–C1a–C2a–C3a–C4a–C5a
N1a–C5a–C6a–N2a
C7a–C8a–C9a–C10a–C11a–C12a
2.711(5)
49.723(5)
47.746(5)
N1b–C1b–C2b–C3b–C4b–C5b
N1b–C5b–C6b–N2b
C7b–C8b–C9b–C10b–C11b–C12b
1.505(5)
47.063(5)
45.754(6)
ꢁ0.266(2)
ꢁ1.573(3)
ꢁ3.492(3)
Although the molecules stack in the a direction in a head to tail
fashion, the phenyl rings of the ligands are on one side and are
approximately parallel to each other. Therefore, there is partial
overlapping between these moieties with a nearest distance of
3.35 Å between the parallel the planes.
3.2.2. [Pt(B)Cl2]ꢀ1/4CH3CN (2ꢀ1/4CH3CN)
Compound 2 crystallizes with two molecules per asymmetric
unit (molecule A and B) showing some conformational differences
(Fig. 4). The crystal structure of complex 2 consists of monomeric
cis-[Pt(B)Cl2] molecules. The Pt center has a typical square planar
geometry in which the largest deviation from the mean coordina-
tion plane is 0.089(2) Å (in N1a) and ꢁ0.064(2) Å (in N1b), very
similar to that of [Pt(A)Cl2]. The average Pt–Cl and Pt–N bond
lengths (2.020, 2.291 Å) can be regarded as normal compared with
the distances reported in the literature (Pt–Cl: 2.281–2.311 Å and
Pt–N: 1.998–2.014 Å) [8,14]. The N(1a)–Pt(1a)–N(2a) and N(1b)–
Pt(1b)–N(2b) bite angles, 79.5(4) and 80.7(4)°, are similar to those
found in 1 and structurally related compounds, e.g. [PtCl2L]
(L = pyridinecarboxaldimines derivative) (79.79°) [14]. The values
for the dihedral angles of N1a–C5a–C6a–N2a and N1b–C5b–C6b–
N2b are ꢁ1.573(3)° and ꢁ3.492(3)°, and comparison of the dihe-
dral angles between the chelate rings and pyridine groups (Table
5) indicates the coplanarity of these moieties. However, the ligand
is not completely planar. The phenyl groups are slightly twisted
with respect to these moieties. In the structure of 2, the plati-
num–platinum vector is inclined by 14.15(9)° with respect to the
coordination plane. The platinum atoms are shifted by 2.34(1) Å
towards the ligand in the a direction. As a consequence, the mole-
cules no longer overlap with the halogen ligands sandwiched be-
tween the chelate planes and vice versa, but there are partially
Fig. 5. Crystal packing of 2, the stacking occurs along the b-axis.
13.08(11)° with respect to the perpendicular of the coordination
plane, and the platinum atoms are not placed orthogonally on
top of one another. Instead, they are shifted by 2.14(6) Å in the
direction towards the ligand. Most of the reported values for PtꢀꢀꢀPt
interactions are in the range 3.09–3.40 Å [13,18,41]. The PtꢀꢀꢀPt sep-
aration is too long to support a significant metal–metal interaction.

S. Dehghanpour et al. / Polyhedron 29 (2010) 2190–2195
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2195
overlapping ligands with a nearest distance between the parallel
pyridine planes of 3.09(2) Å. Again, the molecules stack in the b
direction in a head to tail fashion with two different PtꢀꢀꢀPt dis-
tances (Fig. 5). In this arrangement, the short PtꢀꢀꢀPt distance is
3.62(8) Å. The second PtꢀꢀꢀPt distance is much longer (5.41(9) Å)
and PtꢀꢀꢀPtꢀꢀꢀPt chain angle is 113.91(2)°.
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Four Pt complexes, [Pt(NN)Cl2] (NN = (4-fluorophenyl)pyridin-
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bands at about 424 nm, corresponding to a MLCT transition. In
general, these complexes show two reduction waves at potentials
ranging from ꢁ1.75 to ꢁ1.12 V. An irreversible oxidation is also ob-
served in the anodic region for complexes 1–4 at about +0.67 V.
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CCDC 753586 and 753586 contain the supplementary crystallo-
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Acknowledgment
Financial support by Alzahra University is gratefully
acknowledged.
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