Synthesis, structures, and properties of palladium(II) and platinum(II) complexes with didentate ligands derived from 1-phenylazo-2-naphthylamine and 2-(diphenylphosphino)benzaldehyde or 2-(tert-butylthio)benzaldehyde

Article abstract of DOI:10.1016/S0020-1693(03)00335-9

New palladium(II) and platinum(II) complexes with didentate ligands derived from 1-phenylazo-2-naphthylamine and 2-(diphenylphosphino)benzaldehyde or 2-(tert-butylthio)benzaldehyde have been prepared and their structures are determined by X-ray crystallography. The palladium(II) and platinum(II) complexes containing a phosphorus donor atom ([MCl₂(L¹)] (M=Pd²⁺ (1), Pt²⁺ (2))) are mononuclear, whereas the complex containing a sulfur donor atom ([PdCl(L²)]₃ (3)) has a trinuclear structure. The three palladium atoms of complex 3 are bound to each other through bridging sulfur (thiolato) donor atoms and a six-membered ring (Pd₃S₃) is formed. Complex 3 reacts with potassium iodide in acetonitrile to yield a dinuclear complex, [PdI(L²)] ₂ (4), which has a bent structure. The short Pd-Pd distance (2.8855(7) ?) of complex 4 suggests a Pd-Pd bonding interaction. The coordinated ligands (L¹ and L²) contain a six-membered heterocyclic ring, whose bond and electronic structures are also discussed.

Full text of DOI:10.1016/S0020-1693(03)00335-9

Inorganica Chimica Acta 355 (2003) 197ꢂ204
/
www.elsevier.com/locate/ica
Synthesis, structures, and properties of palladium(II) and
platinum(II) complexes with didentate ligands derived from 1-
phenylazo-2-naphthylamine and 2-(diphenylphosphino)benzaldehyde
or 2-(tert-butylthio)benzaldehyde
Zhicheng Zhu a, Tomohiro Kajino a, Masaaki Kojima b, Kiyohiko Nakajima a,*
a Department of Chemistry, Aichi University of Education, Kariya, Aichi 448-8542, Japan
b Faculty of Science, Department of Chemistry, Okayama University, Tsushima, Okayama 700-8530, Japan
Received 3 March 2003; accepted 18 April 2003
Abstract
New palladium(II) and platinum(II) complexes with didentate ligands derived from 1-phenylazo-2-naphthylamine and 2-
(diphenylphosphino)benzaldehyde or 2-(tert-butylthio)benzaldehyde have been prepared and their structures are determined by X-
ray crystallography. The palladium(II) and platinum(II) complexes containing a phosphorus donor atom ([MCl2(L1)] (MꢀPd2ꢁ
/
(1), Pt2ꢁ (2))) are mononuclear, whereas the complex containing a sulfur donor atom ([PdCl(L2)]3 (3)) has a trinuclear structure.
The three palladium atoms of complex 3 are bound to each other through bridging sulfur (thiolato) donor atoms and a six-
membered ring (Pd3S3) is formed. Complex 3 reacts with potassium iodide in acetonitrile to yield a dinuclear complex, [PdI(L2)]2 (4),
˚
which has a bent structure. The short Pdꢀ
/
Pd distance (2.8855(7) A) of complex 4 suggests a Pdꢀ
/
Pd bonding interaction. The
coordinated ligands (L1 and L2) contain a six-membered heterocyclic ring, whose bond and electronic structures are also discussed.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Palladium(II) complexes; Platinum(II) complexes; Crystal structures; Six-membered heterocyclic ring
1. Introduction
extensively investigated from both fundamental and
applied points of view [1]. It is reported that azo anion
radicals are formed by the addition of an electron to the
low-lying azo-p* orbital [2]. The coordination property
and reactivity of the azo compounds are expected to
relate closely to the electronic structure of the azo group.
Our current research focuses on the synthesis of
photoreactive metal complexes. In a previous paper,
we reported the photochromic reversible substitution of
ruthenium(II) complexes with tri- or tetradentate Schiff
base ligands derived from aromatic aldehyde and
aminoalcohol or diamine [3]. Accordingly, we planned
to prepare the complexes with new azo ligands that were
obtained by the reactions of aromatic aldehydes and
azoamine compounds, and expected new photoreactions
for them. We obtained the palladium(II) and plati-
num(II) complexes with the ligands derived from 1-
Azo compounds have long been investigated, parti-
cularly in connection with the development of new dyes.
In addition, it is well known that photoisomerization
(trans l
pꢂp* and nꢂ
/
cis) of azobenzene occurs by irradiation of the
/
/
p* bands with UV light. Recently, research
interest has focused on the photo- and thermochromic
properties of metal complexes containing azo ligands,
because they are applicable to optical sensors, photo-
switching devices, molecular memory storage, and so
on. Thus, the metal complexes containing such ligands
as azoimines, azophenols, and azooxims have been
* Corresponding author.
E-mail address: knakajim@auecc.aichi-edu.ac.jp (K. Nakajima).
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00335-9

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Z. Zhu et al. / Inorganica Chimica Acta 355 (2003) 197ꢂ204
/
2.2.2. [PtCl2(L1)] (2)
Complex 2 was prepared according to the same
procedure as that described for complex 1, except that
[PtCl2(PhCN)2] was used instead of [PdCl2(PhCN)2].
The crude product was recrystallized from
dichloromethaneꢂ
32.1%. Found: C, 52.50; H, 3.39; N, 5.05. Calc. for
[PtCl2(L1)]×
H2OꢁC35H28Cl2N3OPPt: C, 52.31; H, 3.51;
N, 5.23%. H NMR (chloroform-d) dꢀ8.18 (d, 1H),
8.00 (d, 1H), 7.98 (d, 1H), 7.89 (s, 1H), 7.27ꢂ7.68 (m,
Vis {dichloro-
/
n-hexane to yield red crystals. Yield:
/
/
1
/
Fig. 1. Schematic representation of the ligands (L1 and L2) (a) and the
feasible Schiff base ligand (b).
/
17H), 7.08ꢂ
/
7.17 (m, 4H) ppm. UVꢂ
/
methane, s 10ꢃ3 cmꢃ1 (log o (Mꢃ1 cmꢃ1))} 18.7
(3.94), 22.6 (4.01), 23.6 (3.98 sh), 30.7 (3.99 sh), 32.9
(4.13), 38.0 (4.42 sh).
phenylazo-2-naphthylamine and 2-(diphenylphosphi-
no)benzaldehyde or 2-(tert-butylthio)benzaldehyde
(Fig. 1(a)). In this report, we describe their structures
and properties.
2.2.3. [PdCl(L2)]3 (3)
1-Phenylazo-2-naphthylamine (0.079 g, 0.32 mmol)
was added to a methanol solution (20 cm3) of 2-(tert-
butylthio)benzaldehyde (0.062 g, 0.32 mmol) and the
solution was refluxed for 2 h. A methanol solution (20
cm3) of [PdCl2(PhCN)2] (0.118 g, 0.31 mmol) was added
with stirring, and the reaction mixture was refluxed for 3
h to yield a red precipitate, which was filtered, washed
with methanol (10 cm3), and air-dried at room tempera-
ture. The reaction product was dissolved in dichloro-
2. Experimental
2.1. General procedures
[PdCl2(PhCN)2] [4] and [PtCl2(PhCN)2] [5] were
prepared according to the literature procedure. 1H
NMR spectra were recorded at 400 MHz on a JEOL
JNM LA-400 spectrometer with TMS as an internal
reference. IR spectra were obtained with a Perkinꢂ
Elmer Spectrum 2000 spectrophotometer. UVꢂVis
methane (20 cm3)ꢂN,N-dimethylformamide (1 cm3). By
/
/
slow diffusion of ethanol to the solution, red crystals of
complex 3 were obtained. Yield: 0.133 g, 80.6%. Found:
/
spectra were measured on a Shimadzu UV-2500PC
spectrophotometer.
C, 53.86; H, 3.30; N, 8.15. Calc. for [PdCl(L2)]3×
C69H50Cl3N9OPd3S3: C, 53.71; H, 3.27; N, 8.17%. H
/
H2Oꢁ
/
1
NMR (chloroform-d) dꢀ8.54 (s, 1H), 8.50 (d, 1H), 8.40
(s, 1H), 8.22 (d, 1H), 8.14 (d, 1H), 8.13 (d, 1H), 8.06 (s,
1H), 7.96 (d, 2H), 7.78 (d, 3H), 7.71 (d, 1H), 7.66 (d,
/
2.2. Preparations
2.2.1. [PdCl2(L1)] (1)
1H), 7.12ꢂ7.58 (m, 31H), 7.04 (d, 1H), 7.02 (d, 1H), 6.94
/
1-Phenylazo-2-naphthylamine (0.040 g, 0.16 mmol)
was added to a methanol solution (30 cm3) of 2-
(diphenylphosphino)benzaldehyde (0.046 g, 0.16
mmol). The solution was refluxed for 2 h and evapo-
rated to dryness. The red oily residue was dissolved in
dichloromethane (30 cm3) and [PdCl2(PhCN)2] (0.058 g,
0.15 mmol) was added with stirring. The red reaction
mixture was refluxed for 6 h and evaporated to a small
volume. n-Hexane (20 cm3) was added to the solution to
yield a dark red precipitate, which was filtered and
washed with ether. The crude product was dissolved in a
small amount of acetonitrile and diethyl ether was
added slowly. The mixture was left at room temperature
for several days to yield red prismatic crystals. Yield:
0.086 g, 80.3%. Found: C, 59.63; H, 3.81; N, 7.30. Calc.
(d, 1H) ppm. UVꢂ
Vis {dichloromethane, s 10ꢃ3 cmꢃ1
/
(log o (Mꢃ1 cmꢃ1))} 18.8 (4.43), 23.2 (4.60 sh), 24.0
(4.61), 32.3 (4.85), 40.4 (5.10).
2.2.4. [PdI(L2)]2 (4)
Potassium iodide (0.010 g, 0.059 mmol) was added to
an acetonitrile solution (10 cm3) of complex 3 (0.018 g,
0.012 mmol), and the reaction mixture was refluxed for
5 h to yield a red precipitate, which was filtered and air-
dried. The crude product was dissolved in dichloro-
methane (20 cm3) and insoluble materials were removed
by filtration. The filtrate was evaporated to a small
volume (ca. 5 cm3) followed by addition of n-hexane (20
cm3) to yield dark red crystals. Yield: 0.019 g, 85.0%.
for [PdCl2(L1)]×
60.27; H, 3.86; N, 6.83%. 1H NMR (chloroform-d)
dꢀ8.17 (d, 1H), 8.03 (d, 1H), 8.01 (d, 1H), 7.79 (m,
1H), 7.27ꢂ
/
0.5CH3CNꢁ
/
C36H27.5Cl2N3.5PPd: C,
Found: C, 45.58; H, 2.58; N, 7.17. Calc. for [PdI(L2)]2ꢁ
C46H32I2N6Pd2S2: C, 46.06; H, 2.69; N, 7.01%. 1H
NMR (chloroform-d) dꢀ8.29 (s, 2H), 8.14 (d, 2H),
7.67 (dd, 2H), 7.63 (d, 4H), 7.21ꢂ7.49 (m, 16H), 7.17 (t,
/
/
/
/
7.66 (m, 17H), 7.08ꢂ
/
7.20 (m, 4H) ppm. UVꢂ
/
/
Vis {dichloromethane, s 10ꢃ3 cmꢃ1 (log o (Mꢃ1
cmꢃ1))} 18.9 (3.96), 23.2 (3.96), 24.1 (3.94 sh), 31.2
(4.08 sh), 34.0 (4.27 sh), 38.0 (4.50 sh), 41.2 (4.70).
2H), 7.11 (t, 2H), 7.00 (d, 2H) ppm. UVꢂVis {dichlor-
/
omethane, s 10ꢃ3 cmꢃ1 (log o (Mꢃ1 cmꢃ1))} 19.2
(4.19), 23.4 (4.32 sh), 24.3 (4.33), 32.3 (4.72), 40.0 (4.88).

Z. Zhu et al. / Inorganica Chimica Acta 355 (2003) 197ꢂ
/204
199
Table 1
Crystallographic data and experimental details
Compound
Formula
1×
/
0.5CH3CN
2×
/
H2O
3×
/
4H2O
4×0.5CH2Cl2
/
C36H27.5Cl2N3.5PPd
714.42
C35H28Cl2N3OPPt
803.60
C69H56Cl3N9O4Pd3S3
1597.00
triclinic
C46.5H33ClI2N6Pd2S2
1241.99
triclinic
M
Crystal system
Space group
Unit cell dimensions
monoclinic
C2/c
monoclinic
C2/c
¯
P1
¯
P1
/
/
˚
a (A)
31.031(4)
11.391(2)
18.913(3)
30.771(3)
11.438(1)
18.840(2)
17.621(3)
19.180(4)
14.754(3)
110.049(9)
97.541(8)
106.281(7)
4351(1)
2
12.5901(8)
16.538(1)
11.7903(8)
97.132(3)
99.306(3)
86.345(3)
2401.5(3)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
100.415(3)
100.640(5)
g (8)
3
V (A )
˚
6574(1)
8
8.06
6516(1)
8
45.34
Z
m(Mo Ka) (cmꢃ1
Transmission factor
Crystal color
)
8.21
22.16
0.9843ꢂ/0.9891
0.5512ꢂ/0.6826
0.7316ꢂ/0.8022
0.6033ꢂ0.7334
/
red
prism
red
prism
red
prism
red
prism
Crystal habit
Crystal size (mm3)
Dcalcd (g cmꢃ3
2umax (8)
R1 (R) a
Rw
0.13ꢄ
1.449
55.0
/0.16ꢄ
/0.20
0.20ꢄ
1.638
55.0
/
0.30ꢄ
/
0.30
0.20ꢄ
1.219
55.0
/
0.30ꢄ
/
0.40
0.16ꢄ
1.717
55.0
/0.30ꢄ0.30
/
)
0.052
0.065 b
1.34
0.048
0.069 b
1.97
0.079 (0.133)
0.236 c
2.71
0.058
0.098 b
2.89
d
S
a
R1ꢀ
/
SjjFojꢃ
/
jFcjj/SjFoj, where R is obtained for all observed data.
2 1/2
/
b
c
Rw
Rw
ꢀ
ꢀ
/
[Sw(jFojꢃ
jFcj)2/SwjFoj ]
.
2
2 2
2 2 1/2
/
[Sw(jFoj ꢃ
/
jFcj ) /Sw(jFoj ) ]
.
d
Sꢀ
/
[Sw(jFojꢃ
/
jFcj)2/(mꢃ
/
n)]1/2 (mꢀ
/
no. of used reflections, nꢀno. of refined parameters).
/
2.3. X-ray crystallography
3. Results and discussion
Crystallographic data and experimental details for
complexes 1, 2, 3 and 4 are summarized in Table 1. Each
single crystal of complexes 1, 2 and 4 was glued on a
glass fiber and coated with epoxy resin and that of
complex 3 was sealed in a glass capillary with the mother
liquor to prevent loss of the solvent of crystallization. X-
ray diffraction data were collected on a Rigaku RAXIS-
3.1. Structures of [PdCl2(L1)] (1) and [PtCl2(L1)]
(2)
Complex 1 was prepared in good yield by treating
[PdCl2(PhCN)2] with the reaction mixture of 1-pheny-
lazo-2-naphthylamine and 2-(diphenylphosphino)ben-
zaldehyde in dichloromethane. Complex
2
was
RAPID diffractometer using graphite-monochromated
˚
0.71069 A). A numerical absorp-
prepared in a similar manner as complex 1 by using
[PtCl2(PhCN)2] instead of [PdCl2(PhCN)2]. Crystals of
complexes 1 and 2 were grown by diffusion of diethyl
ether (for complex 1) and n-hexane (for complex 2) into
each solution of the complex in acetonitrile (for complex
1) and dichloromethane (for complex 2) at room
temperature, and their structures were determined by
an X-ray method. The structures of both complexes
were similar to each other, and Fig. 2 shows a
perspective view of complex 1 representatively. The
selected bond distances and angles of complexes 1 and
2 are summarized in Table 2. We expected that the
complexes containing a tridentate Schiff base ligand
(Fig. 1(b)) would be prepared by the reaction; however,
complexes 1 and 2 had didentate ligand L1 (Fig. 1(a)).
The coordination geometry around the Pd atom is
square-planar with a small distortion. The strong trans
Mo Ka radiation (lꢀ
/
tion correction using the program NUMABS [6] was
applied to the intensity data. The structures were solved
by direct methods (SIR92 [7]) and expanded using
Fourier techniques (DIRDIF94 [8]). The structures
were refined by full-matrix least-squares based on F
(1, 2 and 4) and F2 (3) with anisotropic displacement
parameters for all non-hydrogen atoms except those of
the disordered solvent molecules of crystallization
incorporated in the crystal lattice. The relatively high
R-factor value for complex 3 is due to the disorder of
crystallization water. Hydrogen atoms were placed at
idealized positions and included in the refinement, but
not refined. All calculations were performed using the
teXsan [9] crystallographic software package of Mole-
cular Structure Corporation.

200
Z. Zhu et al. / Inorganica Chimica Acta 355 (2003) 197ꢂ204
/
Scheme 1.
influence of the coordinating P(1) atom is reflected in
the PdꢀCl bonds; that is, the bond length of Pd(1)ꢀCl(2)
/
/
˚
(2.349(2) A) is considerably longer than that of Pd(1)ꢀ
/
˚
Cl(1) (2.278(2) A). The N(3) atom is attached to the C(7)
atom, and a six-membered ring composed of C(7), N(1),
C(8), C(9), N(2) and N(3) atoms is formed. The C(7)
˚
atom is 0.573(7) A out of the mean plane defined by
N(1), C(8), C(9), N(2), and N(3) atoms. The bond
˚
C(7) (1.477(6)
lengths (N(1)ꢀ
/
C(7) (1.464(6) A), N(3)ꢀ
/
˚
˚
A), C(1)ꢀ
single bond lengths, and that of N(2)ꢀ
indicates an NꢁN double bond. The bond angles
/
C(7) (1.526(7) A)) are in the range of common
˚
N(3) (1.329(6) A)
/
/
around the N(3) atom (117.3(4)ꢂ121.2(4)8) suggest
/
that the N(3) atom is sp2-hybridized. These results are
consistent with those of the expected structure of
complex 1, which is illustrated in Scheme 1(a). However,
Fig. 2. An ORTEP drawing of complex 1 with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability.
˚
the bond lengths of N(1)ꢀ
C(9) (1.322(6) A) indicate Cꢁ
/
C(8) (1.320(7) A) and N(2)ꢀ
/
˚
/
N double bonds. Accord-
Table 2
˚
Selected bond lengths (A) and angles (8) for complexes 1 and 2
1 (Mꢀ/Pd)
2 (Mꢀ/Pt)
1 (Mꢀ
/
Pd)
2 (MꢀPt)
/
M(1)ꢀ
M(1)ꢀ
M(1)ꢀ
M(1)ꢀ
N(1)ꢀ
N(1)ꢀ
N(2)ꢀ
N(2)ꢀ
N(3)ꢀ
N(3)ꢀ
C(1)ꢀ
/
Cl(1)
Cl(2)
P(1)
2.278(2)
2.349(2)
2.256(1)
2.017(4)
1.464(6)
1.320(7)
1.329(6)
1.322(6)
1.477(6)
1.419(6)
1.526(7)
2.291(2)
2.346(2)
2.229(2)
1.997(6)
1.47(1)
C(8)ꢀ
C(8)ꢀ
C(9)ꢀ
/
C(9)
C(17)
C(10)
1.452(7)
1.437(7)
1.461(7)
1.387(9)
1.389(9)
1.417(9)
1.36(1)
1.45(1)
1.45(1)
1.47(1)
1.41(1)
1.43(1)
1.40(1)
1.41(2)
1.36(2)
1.43(1)
1.43(1)
1.34(1)
/
/
/
/
/N(1)
C(10)ꢀ
C(10)ꢀ
C(11)ꢀ
C(12)ꢀ
C(13)ꢀ
C(14)ꢀ
C(15)ꢀ
C(16)ꢀ
/
C(11)
C(15)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
/
C(7)
C(8)
N(3)
C(9)
C(7)
C(18)
/
/
1.319(9)
1.322(9)
1.31(1)
/
/
/
/
/
1.36(1)
/
1.450(9)
1.425(9)
1.54(1)
/
1.41(1)
1.44(1)
1.356(9)
/
/
/
C(7)
M(1)ꢀ
M(1)ꢀ
M(1)ꢀ
M(1)ꢀ
M(1)ꢀ
/
Cl(1)ꢀ
Cl(1)ꢀ
Cl(1)ꢀ
Cl(2)ꢀ
Cl(2)ꢀ
P(1)ꢀM(1)ꢀ
M(1)ꢀN(1)ꢀ
M(1)ꢀN(1)ꢀ
N(3)ꢀN(2)ꢀ
N(2)ꢀN(3)ꢀ
/
/
Cl(2)
P(1)
N(1)
P(1)
N(1)
90.85(6)
89.12(6)
176.2(1)
173.90(6)
90.5(1)
90.00(8)
90.26(8)
177.5(2)
175.28(8)
89.5(2)
N(2)ꢀ
N(1)ꢀ
N(1)ꢀ
N(3)ꢀ
N(1)ꢀ
N(1)ꢀ
C(9)ꢀC(8)ꢀ
N(2)ꢀC(9)ꢀ
N(2)ꢀC(9)ꢀ
C(8)ꢀC(9)ꢀ
/
N(3)ꢀ
C(7)ꢀ
C(7)ꢀ
C(7)ꢀ
C(8)ꢀ
C(8)ꢀ
/
C(18)
117.3(4)
108.2(4)
109.1(4)
112.8(4)
119.4(5)
122.0(5)
118.6(5)
120.9(5)
117.9(5)
120.5(5)
118.0(6)
109.5(6)
109.1(6)
112.3(6)
119.4(7)
122.8(7)
117.8(7)
120.8(7)
118.4(7)
120.3(7)
/
/
/
/
N(3)
C(1)
C(1)
C(9)
C(17)
/
/
/
/
/
/
/
/
/
/
/
/
/
/
N(1)
89.9(1)
90.4(2)
/
/
/
/
C(7)
116.0(3)
126.5(4)
117.0(4)
119.9(4)
116.4(5)
127.1(5)
117.5(6)
119.1(6)
/
/
C(17)
/
/
C(8)
/
/C(8)
/
/
C(9)
/
/C(10)
/
/
C(7)
/
/
C(10)

Z. Zhu et al. / Inorganica Chimica Acta 355 (2003) 197ꢂ
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201
ingly, a resonance hybrid of the two structures 1a and 1b
(Scheme 1) may be the most reasonable representation
of complex 1.
It could be presumed that the didentate L1 ligand
(Fig. 1(a)) is in equilibrium with the tridentate Schiff
base ligand (Fig. 1(b)) in dichloromethane; however, our
efforts to isolate either of them were unsuccessful.
view of complex 3, and selected bond distances and
angles are summarized in Table 3. The structure of
complex 3 appears to be trinuclear, where each Pd atom
has a square-planar geometry. De-tert-butylation of the
ligand occurred during preparation of the complex. It is
t
reported that de-tert-butylation of the Buꢂ
/S moiety
occurs upon coordination of sulfur to metal ions with
high Lewis acidity, such as Ni2ꢁ, Cu2ꢁ, Zn2ꢁ and Cuꢁ
[10]. In a previous paper, we prepared [RuCl2(btb-en)]
3.2. Structure of [PdCl(L2)]3 (3)
(btb-enꢀN,N?-bis(2-tert-butylthiobenzilidene)-1,2-
/
t
ethanediamine), where the Bu group attached persis-
tently to the coordinated S atoms [3a]. On the other
hand, the de-tert-butylated complex of [M(tsal-en)]
Complex 3 was obtained by treating [PdCl2(PhCN)2]
with the reaction mixture of 1-phenylazo-2-naphthyla-
mine and 2-(tert-butylthio)benzaldehyde in dichloro-
methane. The complex crystallized with four water
molecules of crystallization. Fig. 3 shows a perspective
(Mꢀ
1,2-ethanediamine) was obtained by the reaction of
btb-en and NiCl2×H2O [11] or [PdCl2(cod)] [12] (codꢀ
1,5-cyclooctadiene). These results suggest that de-tert-
S moiety occurs readily upon
/
Ni2ꢁ
,
Pd2ꢁ
;
tsal-enꢀ
/
N,N?-dithiosalicylidene-
/
/
butylation of the tBuꢂ
/
coordination of sulfur to Pd2ꢁ but not with the Ru2ꢁ
ion. The L2 ligand and the Clꢃ ligand occupy three of
the four coordination sites, and a bridging sulfur atom
of the neighboring ligand fills the fourth site. The core of
complex 3 consists of a six-membered ring of alternating
Pd and S atoms in a twist-boat conformation. The bond
angles involving bridging sulfur atoms are: Pd(1)ꢀ
Pd(2), 109.93(8)8; Pd(2)ꢀS(2)ꢀPd(3), 104.20(8)8; Pd(1)ꢀ
S(3)ꢀPd(3), 97.53(8)8. The deviations of the Pd atoms
from the least-squares planes of the PdS2NCl set are
/
S(1)ꢀ
/
/
/
/
/
˚
˚
0.0054(9) A (for Pd(1) (plane 1)), 0.0199(9) A (for Pd(2)
˚
(plane 2)) and 0.0013(10) A (for Pd(3) (plane 3)), and the
coordination planes form dihedral angles of 112.08(7)8
(planes 1 and 2), 93.75(7)8 (planes 1 and 3) and 98.23(7)8
(planes 2 and 3). The Nꢀ
/
C and Nꢀ
/
N bond lengths that
are included in the coordinated L2 ligand are essentially
similar to those of the L1 ligand in complexes 1 and 2.
The distances between the Pd atoms (Pd(1)ꢀ
/
Pd(2),
˚
˚
3.7627(8) A; Pd(1)ꢀ
/
Pd(3), 3.4812(8) A; Pd(2)ꢀ
/
Pd(3),
˚
3.6856(8) A) indicate that there are no direct bonds.
Trinuclear palladium(II) and nickel(II) complexes con-
taining thiolato sulfur bridges have been reported. For
example, [Ni(mpg)]3×
(2-mercaptopropionyl)glycine), [Pd(4MeOAp4Me2)]3×
DMSO [14] (4MeOAp4Me2ꢀ2-hydroxy-4-methoxyace-
tophenone N4-dimethylthiosemicarbazone dianion) and
[Ni(bit)3] [15] (H2bitꢀ2-(OH)C6H4CHꢁN(CH2)2SH)
have a chair-like conformation of M3S3 (Mꢀ
Pd2ꢁ or
Ni2ꢁ) six-membered rings. It seems that the conforma-
DMF [16] (Ap4Eꢀ2-hydroxyace-
/
3MeOH×
/
0.5Et2O [13] (mpgꢀ
/
N-
/
/
/
/
/
tion in [Pd(Ap4E)]3×
/
/
tophenone N4-ethylthiosemicarbazone dianion) is
similar to complex 3. The Pd3S3 six-membered ring of
complex 3 cannot have a chair-like conformation
because of the steric repulsion between the adjacent
ligands. Thus the conformational stability of the M3S3
ring is presumably affected by the steric bulkiness of the
coordinated ligands.
Fig. 3. An ORTEP drawing of complex 3 with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability. The Pd3S3 six-
membered ring has a twist-boat conformation.

202
Z. Zhu et al. / Inorganica Chimica Acta 355 (2003) 197ꢂ204
/
Table 3
˚
Selected bond lengths (A) and angles (8) for complex 3
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
N(2)ꢀ
/
Cl(1)
2.316(2)
2.280(2)
2.310(2)
2.022(6)
1.34(1)
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
N(5)ꢀ
/
Cl(2)
2.348(2)
2.315(2)
2.312(2)
2.059(6)
1.318(9)
Pd(3)ꢀ
Pd(3)ꢀ
Pd(3)ꢀ
Pd(3)ꢀ
N(8)ꢀ
/
Cl(3)
2.327(2)
2.359(2)
2.319(2)
2.040(7)
1.29(1)
/S(1)
/S(1)
/S(2)
/S(3)
/S(2)
/S(3)
/N(1)
/N(4)
/N(7)
/
N(3)
/
N(6)
/
N(9)
Cl(1)ꢀ
Cl(1)ꢀ
Cl(1)ꢀ
S(1)ꢀPd(1)ꢀ
S(1)ꢀPd(1)ꢀ
S(3)ꢀPd(1)ꢀ
Cl(2)ꢀ
Cl(2)ꢀ
Cl(2)ꢀ
S(1)ꢀPd(2)ꢀ
S(1)ꢀPd(2)ꢀ
S(2)ꢀPd(2)ꢀ
Cl(3)ꢀ
Cl(3)ꢀ
/
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
/
S(1)
176.4(1)
95.37(8)
91.4(2)
Cl(3)ꢀ
S(2)ꢀPd(3)ꢀ
S(2)ꢀPd(3)ꢀ
S(3)ꢀPd(3)ꢀ
Pd(1)ꢀS(1)ꢀ
Pd(1)ꢀS(1)ꢀ
Pd(2)ꢀS(1)ꢀ
Pd(2)ꢀS(2)ꢀ
Pd(2)ꢀS(2)ꢀ
Pd(3)ꢀS(2)ꢀ
Pd(1)ꢀS(3)ꢀ
Pd(1)ꢀS(3)ꢀ
Pd(3)ꢀS(3)ꢀ
/
Pd(3)ꢀN(7)
/
89.9(2)
/
/S(3)
/
/
S(3)
91.05(7)
174.3(2)
86.6(2)
/
/N(1)
/
/N(7)
/
/
S(3)
84.02(7)
89.5(2)
/
/N(7)
/
/N(1)
/
/Pd(2)
109.93(8)
112.0(3)
103.2(2)
104.20(8)
108.8(3)
107.7(2)
97.53(8)
106.3(3)
112.1(3)
/
/N(1)
171.8(2)
86.85(8)
170.59(8)
92.9(2)
/
/C(2)
/
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
/
S(1)
S(2)
N(4)
/
/C(2)
/
/
/
/
Pd(3)
C(25)
N(25)
Pd(3)
C(48)
C(48)
/
/
/
/
/
/S(2)
90.53(7)
174.2(2)
90.6(2)
/
/
/
/N(4)
/
/
/
/N(4)
/
/
/
Pd(3)ꢀ
/
S(2)
92.53(8)
176.41(8)
/
/
/
Pd(3)ꢀ
/
S(3)
3.3. Structure of [PdI(L2)]2 (4)
complex 4 is depicted in Fig. 4 and selected bond
distances and angles are summarized in Table 4. The
complex is dinuclear and crystallizes with a dichloro-
methane molecule incorporated in the crystal lattice.
The L2 ligand bridges two Pd atoms with its thiolato
sulfur atom. The coordination geometry around each Pd
atom is essentially square-planar, and the deviations of
the Pd atoms from the least-squares planes of the
We tried to oxidize complex 3 using iodine in
dichloromethane, however, no oxidation products were
obtained. When potassium iodide was added to the
acetonitrile solution of complex 3, the color of the
solution changed from red to brown and complex 4
crystallized out of the solution. A perspective view of
˚
PdS2NI set are 0.0279(6) A (for Pd(1) (plane 1)) and
˚
0.0300(7) A (for Pd(2) (plane 2)). The folding angle
between the two coordination planes of 100.34(4)8 is
surprisingly small, and a Pd(1)ꢀ
2.8855(7) A is observed, which suggests a PdꢀPd
/
Pd(2) distance of
˚
/
bonding interaction. There are many studies on the
structures of double-bridged dinuclear complexes of the
type [M2(m-SRn)2L4] (Rꢀ
/
alkyl; Lꢀ
Clꢃ, Brꢃ, Iꢃ, CO;
/
nꢀ0ꢂ2) [17]. It is said that the planar structure should
/
/
be highly unstable for the palladium(II) complexes and
Table 4
˚
Selected bond lengths (A) and angles (8) for complex 4
Pd(1)ꢀ ꢀ ꢀPd(2)
I(1)ꢀPd(1)
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
N(2)ꢀ
2.8855(7)
2.5664(7) I(2)ꢀ
/
/
Pd(2)
2.5637(8)
2.303(2)
2.329(2)
2.030(5)
1.334(9)
/
S(1)
S(2)
N(1)
2.322(2)
2.317(2)
2.030(5)
1.320(8)
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
N(5)ꢀ
/
S(1)
S(2)
N(4)
/
/
/
/
/
N(3)
/N(6)
I(1)ꢀPd(1)ꢀ
I(1)ꢀPd(1)ꢀ
I(1)ꢀPd(1)ꢀ
S(1)ꢀPd(1)ꢀ
S(1)ꢀPd(1)ꢀ
S(2)ꢀPd(1)ꢀ
Pd(1)ꢀS(1)ꢀ
Pd(1)ꢀS(1)ꢀ
Pd(2)ꢀS(1)ꢀ
/
/
S(1)
S(2)
N(1)
173.84(5) I(2)ꢀ
98.65(4) I(2)ꢀ
91.3(1)
I(2)ꢀ
/
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
S(2)ꢀ
S(2)ꢀ
S(2)ꢀ
/
S(1)
S(2)
N(4)
97.17(5)
172.85(5)
94.5(2)
/
/
/
/
/
/
/
/
/
/S(2)
79.25(6) S(1)ꢀ
/
/S(2)
79.38(6)
165.2(2)
88.0(2)
/
/
N(1)
N(1)
Pd(2)
C(2)
C(2)
90.0(2)
167.3(2)
S(1)ꢀ
S(2)ꢀ
/
/
N(4)
N(4)
Pd(2)
C(25)
C(25)
/
/
/
/
Fig. 4. An ORTEP drawing of complex 4 with the atom labeling
scheme. All non-hydrogen atoms are represented by their thermal
displacement vibrational ellipsoids at 30% probability. The bottom
/
/
77.20(5) Pd(1)ꢀ
/
/
76.77(5)
111.1(2)
111.6(2)
/
/
111.0(2)
116.2(2)
Pd(1)ꢀ
Pd(2)ꢀ
/
/
/
/
/
/
view shows the folding angle along the S(1)ꢀS(2) axis.
/

Z. Zhu et al. / Inorganica Chimica Acta 355 (2003) 197ꢂ
/204
203
the bent structure is preferable. It is also reported that
the most favorable ligands for a bonding metalꢀmetal
interaction are those with good s-donor and p-acceptor
character [18]. However, most PdꢀPd distances in
sulfur-bridged dinuclear palladium(II) complexes are
complexes 1 and 2, respectively) are explained by their
tri- and dinuclear structures. The question is whether the
dimeric and trimeric structures of complexes 3 and 4
/
1
/
remain intact in solution. In the H NMR spectra of
trinuclear [Ni(bit)3], it was reported that the signals of a
dinuclear species were observed apart from the major
resonances of the trinuclear compound in CDCl3 [15].
˚
larger than 3.0 A, and that of complex 4 (2.8855(7) A)
˚
is one of the shortest distances that have been reported
˚
1
so far. A short Pdꢀ
/
Pd distance of 2.964(2) A was also
reported in [PdI(o-SC6H4PPh2)]2 [19]. The Iꢃ ligand
We measured the H NMR spectra of the complexes in
dichloromethane-d2. All the complexes gave compli-
could be preferable for the Pdꢀ
/
Pd bonding interaction
cated spectral patterns in the 7.0ꢂ8.6 ppm region,
/
in such dinuclear complexes, although s-basicity of the
however, an important observation is that there is only
one set of sharp resonances in each spectrum at room
temperature. Although, we cannot deny the possibility
of rapid interconversion that is faster than the NMR
time scale between the dinuclear and trinuclear forms, it
seems unreasonable that such a marked structural
transformation of palladium(II) complexes occurs so
rapidly. The structures of complexes 3 and 4 in the solid
state should persist in a non-coordinating solvent such
as dichloromethane.
Iꢃ ligand is weak.
3.4. IR, UVꢂVis and NMR spectra of the complexes
/
It is reported that nNꢁN of 2-(phenylazo)aniline (H2L)
is observed at 1460 cmꢃ1, while the nNꢁN of Pd(HL)2 is
shifted to a lower wavenumber (1340 cmꢃ1) [20]. In the
IR spectra of complexes 1ꢂ
/
4, however, many bands
1450 cmꢃ1 region that were not
appeared in the 1200ꢂ
/
assigned. On the other hand, a band of medium intensity
was observed at 1612 cmꢃ1 (complex 1), 1602 cmꢃ1
(complex 2), 1604 cmꢃ1 (complex 3) and 1614 cmꢃ1
(complex 4). These bands could be assigned to the nCꢁN
of the coordinated ligands (Scheme 1(b)), in view of the
bond lengths of the complexes in the crystal. An
observation of the nCꢁN band (1600 cmꢃ1) of Pd(HL)2
4. Supplementary material
Tables of non-hydrogen atom coordinates and aniso-
tropic thermal parameters, coordinates of the hydrogen
atoms, and bond lengths and angles have been deposited
as CIF files (Nos. 207566ꢂ
the Cambridge Crystallographic Data Center, 12 Union
Road, Cambridge, CB2 1EZ, UK (Fax: ꢁ44ꢂ1223ꢂ
/
207569 for complexes 1ꢂ4) at
/
[20] is consistent with our assignment. The UVꢂVis
/
spectra of the complexes were measured in dichloro-
methane (Fig. 5). The spectra show strong bands in the
visible region, and the spectral patterns are very similar
to one another. The absorption band at ca. 530 nm is
/
/
/
336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
probably due to a transition of the Nꢁ
ligand. The high-intensity band observed at ca. 410ꢂ
nm can be assigned to a combination of dꢂd band and
/
N moiety of the
/440
/
Acknowledgements
charge-transfer transition from the ligand to palladium
(MLCT). The large absorption coefficients of complexes
3 and 4 (three times and twice as large as those of
This work was supported by a Grant-in-Aid for
Scientific Research No. 13640557 from the Ministry of
Education, Science, and Culture.
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