Ruthenium-carbonyl complexes of 1-alkyl-2-(arylazo)imidazoles: Synthesis, structure, spectra and redox properties

Article abstract of DOI:10.1016/j.poly.2008.06.027

trans-(Cl)-[Ru(CO)₂Cl₂(PaiR/TaiR)] compounds have been synthesized by reacting 1-alkyl-2-(phenylazo)imidazole (PaiR) or 1-alkyl-2-(p-tolylazo)imidazoles (TaiR) with [Ru(CO)₂Cl₂]_n in methanol under refluxing conditions. The X-ray crystallographic study of trans-(Cl)-[Ru(CO)₂Cl₂(PaiEt)] (PaiEt = 1-ethyl-2-(phenylazo)imidazole) shows a distorted octahedral geometry with a trans-Cl,Cl configuration. An intermolecular hydrogen bonded dimer serves as a motif in the supramolecular network with C-H?π and π?π interactions. The complexes show metal oxidation, Ru(III)/Ru(II); and reduction of the coordinated azo (-N{double bond, long}N-) function. The molecular orbital diagram has been drawn by density functional theory (DFT) using an optimized geometry from the single crystal X-ray parameters. The electronic movement and assignment of electronic spectra have been carried out by TD-DFT calculations both in the gas and acetonitrile phase.

Full text of DOI:10.1016/j.poly.2008.06.027

Polyhedron 27 (2008) 3020–3028
Contents lists available at ScienceDirect
Polyhedron
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Ruthenium–carbonyl complexes of 1-alkyl-2-(arylazo)imidazoles: Synthesis,
structure, spectra and redox properties
T.K. Mondal a, S.K. Sarker a, P. Raghavaiah b, C. Sinha a,
*
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, West Bengal, India
b School of Chemistry, National Single Crystal X-ray Diffractometer Facility, University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 April 2008
Accepted 3 June 2008
trans-(Cl)-[Ru(CO)2Cl2(PaiR/TaiR)] compounds have been synthesized by reacting 1-alkyl-2-(pheny-
lazo)imidazole (PaiR) or 1-alkyl-2-(p-tolylazo)imidazoles (TaiR) with [Ru(CO)2Cl2]n in methanol under
refluxing conditions. The X-ray crystallographic study of trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (PaiEt = 1-ethyl-
2-(phenylazo)imidazole) shows a distorted octahedral geometry with a trans-Cl,Cl configuration. An
intermolecular hydrogen bonded dimer serves as a motif in the supramolecular network with C–Hꢀ ꢀ ꢀ
p
Keywords:
and interactions. The complexes show metal oxidation, Ru(III)/Ru(II); and reduction of the coordi-
pꢀ ꢀ ꢀp
Azoimidazoles
Ruthenium–carbonyl
X-ray structure
Electrochemistry
DFT calculation
nated azo (–N@N–) function. The molecular orbital diagram has been drawn by density functional theory
(DFT) using an optimized geometry from the single crystal X-ray parameters. The electronic movement
and assignment of electronic spectra have been carried out by TD-DFT calculations both in the gas and
acetonitrile phase.
Ó 2008 Published by Elsevier Ltd.
1. Introduction
of CO2 or the water gas shift reaction [59–61]. They are used as
building blocks for making organometallic-based nanostructures
The tremendous development of the coordination chemistry of
2,2-bipyridine and its applications [1–4] have inspired the design
of N,N-donor ligands in which one of the donor centers comes
from pyridine or a N-heterocycle. Ligands consisting of one N-het-
erocyclic ring with a conjugated pendant azo (–N@N–) group at
the ortho-position give an azoimine (–N@N–C@N–) linkage, iso-
electronic with the diimine function (–N@C–C@N–), and serve
e.g., Ru-wire polymeric materials, [Ru(bpy)(CO)2]n [62]. Among
these, [Ru(CO)2Cl2(bpy)] is the main precursor [63,64]. This has
prompted us to undertake a study of Ru–carbonyl complexes of
azoheterocycles.
We have been engaged for the last few years in the design of
azoimidazole molecules [18–29]. Imidazole and its derivatives
were chosen because of their chemical and biological ubiquity
as an efficient
ity of the azo-N participates through the
p
-acidic ligand [5–40]. The high
p
-acceptance abil-
[65], whilst the azo group enhances p-acidity and is responsible
for photochromism [66–68], pH-responsive and redox activity in
p
*-azo orbital. Conse-
quently, the ligands are able to stabilize metal ions in their
lower oxidation states. Examples are 2-(arylazo)pyridines, whose
ruthenium(II) compounds have been reported in recent years
[48–52,12,53–58] with reference to the exploration of their struc-
tural diversity, electrochemical properties, catalytic and antican-
cer activities.
Ruthenium and osmium carbonyl complexes of azopyridines
act as a CO reservoir and may be used for hydroformylation or
other CO insertion reactions [30–44,6,45,7,46,47]. In organic trans-
formations these metal carbonyls play a crucial role [1–4,41–
44,6,45,7,46,47]. Carbonyl–ruthenium(II) polypyridine complexes
are excellent catalysts and catalyst precursors for the reduction
the molecules [26–44,6,45,7,46–52,12,53–58].
In this work, we report on the reaction of 1-alkyl-2-(ary-
lazo)imidazole [1-alkyl-2-(phenylazo)imidazoles (PaiR, 1) and 1-
alkyl-2-(p-tolylazo)imidazoles (TaiR, 2)] with [Ru(CO)2Cl2]n. The
products are characterized by microanalytical and spectroscopic
data which support the composition, [Ru(CO)2Cl2(PaiR)] (3) and
[Ru(CO)2Cl2(TaiR)] (4). The electronic structures of [Ru(CO)2-
Cl2(PaiEt)] (3b) and [Ru(CO)Cl2(PaiEt)(NCMe)] (5b) have been cal-
culated by DFT and TD-DFT methods. The calculated information
has been used to rationalize the electronic spectra and redox prop-
erties of the complexes:
½RuðCOÞ Cl2ꢁ þ N;N0
!
Reflux;MeOH trans-ðClÞ-½RuðCOÞ Cl2ðN;N0Þꢁ
ð1Þ
ð2Þ
2
n
2
trans-ðClÞ-½RuðCOÞ Cl2ðN;N0Þꢁ þ Me3NO
2
Reflux;MeCN trans-ðClÞ-½RuðCOÞCl2ðN;N0ÞðMeCNÞꢁ
* Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
!
0277-5387/$ - see front matter Ó 2008 Published by Elsevier Ltd.
doi:10.1016/j.poly.2008.06.027

T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
3021
2. Results and discussion
2.1. Synthesis and formulation
Reaction of [Ru(CO)2Cl2]n as a methanol suspension with 1-al-
kyl-2-(phenylazo)imidazole (PaiR) (1) or 1-alkyl-2-(p-tolylazo)-
imidazole (TaiR) (2) (where R = Me (a), CH2CH3 (b), CH2Ph (c))
under refluxing conditions in a dinitrogen atmosphere resulted in
a brown solution Eq. (1). Upon slow evaporation of the solvent a
brown crystalline product was left. The formulation of the com-
plexes, [Ru(CO)2Cl2(PaiR)] (3) and [Ru(CO)2Cl2(TaiR)] (4) have been
supported by microanalytical data (Section 4). Although three geo-
metrical isomers (3 and 4; 30 and 40; 300 and 400) are possible, we
have isolated only one isomer, with the CO groups cis to each other
(3 and 4) and two Cl ligands in a trans disposition (Scheme 1). The
complexes are diamagnetic, indicating the presence of the metal in
the +2 oxidation state (d6). Three stereo-isomers of 3/4, 30/40 and 300/
400 are possible. The structure has been established by a single crys-
tal X-ray diffraction study in the case of [Ru(CO)2Cl2(PaiEt)] and
has a trans-(Cl,Cl) geometry, abbreviated as trans-(Cl)-[Ru(CO)2-
Cl2(PaiR/TaiR)] (3 or 4). The higher stability of the trans-(Cl)-
cis-(CO) isomer relative to the cis-(Cl)-trans-(CO) isomer is not
surprising due to the trans weakening effect of CO. The selectivity
of the trans-(Cl) configuration has also been supported by DFT cal-
culations (vide Section 2.3). Complexes 3 and 4 undergo a selective
mono-decarbonylation reaction upon refluxing with Me3NO in ace-
tonitrile Eq. (2). In this process one CO is released and MeCN is
coordinated, trans-(Cl)-[Ru(CO)Cl2(PaiR)(NCMe)] (5) and trans-
(Cl)-[Ru(CO)Cl2(TaiR)(NCMe)] (6) are formed. The structure of the
mono-carbonylated product (5, 6) is supported by a single stretch
Fig. 1. Molecular structure of two conformers of trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b)
(30% probability ellipsoids).
m
(CO) in the FT-IR spectra (Fig. 1), elemental analysis and 1H NMR
spectroscopic measurements. Although isomerisation to give cis-
(Cl)-[Ru(CO)Cl2(ligand)(NCMe)] is possible, we cannot establish
the presence of this isomer, even in the mixed form. The photo-
chemical treatment of the precursor was also unsuccessful for
isomerisation and giving the full decarbonylated complexes. The
crystals of these complexes are weakly diffracting for X-ray struc-
ture determination. The full removal of CO has not been achieved
even under drastic reaction conditions in the presence of a large
excess of Me3NO [69,70]. This reaction yielded an intractable
brown solid.
2.2. Molecular structure
The X-ray structure of [Ru(CO)2Cl2(PaiEt)] (3b) is shown in Fig.
1; selected bond parameters are listed in Table 1. The ligands dis-
positions determine the structure as trans-(Cl)-[Ru(CO)2Cl2(PaiEt)].
The molecule consists of a central Ru surrounded by six donor cen-
ters, and the arrangement is distorted octahedral. The atomic
arrangement involves two trans-chlorine, two cis-CO and a che-
lated 1-ethyl-2-(phenylazo)imidazole (PaiEt) ligand within the
RuCl2C2N2 coordination sphere. The two CO ligands are trans to
the azo-N and imidazole-N coordinated centers. The asymmetric
unit of the lattice consists of two molecules. A view of the diad,
including the atomic numbering scheme, is given in Fig. 1. In terms
of bond distances and angles, as well as gross geometry, the two
molecules are closely alike to one another. The chelate ring dimen-
sions (\N(3)–Ru(1)–N(1): 75.13(9) and \N(5)–Ru(2)–N(7):
75.28(9)) are comparable with those in other structurally
characterized chelates of the azoimine function [26–29,41–
44,6,45,7,46–52,12,53–58]. The trans chlorine angles, Cl(4)–
Ru(1)–Cl(5), 177.14(3) and Cl(3)–Ru(2)–Cl(6), 176.04(3), lie in the
range of reported data [51,52,12,53–58]. Other angles about Ru de-
fine the distorted octahedral geometry.
4
5
4
5
N
N
N
N
N
N
R
R
N
N
N
N
9
11
10
7
8
7
8
11
10
Me
(PaiR)(1)
(TaiR)(2)
The Ru–N(azo) distance (Ru(1)–N(1), 2.132(2); Ru(2)–N(5),
2.123(2) Å) is slightly longer than Ru–N(imidazole) (Ru(1)–N(3),
2.102(2); Ru(2)–N(7), 2.106(2) Å). In general, the Ru–N(azo) bond
distance is shorter than the Ru–N(imidazole) bond, which is
R = Me (a), CH2CH3 (b), CH2Ph (c); N = imidazole-N, N/ = azo-N
Cl
CO
Ru
Cl
Cl
CO
CO
Cl
Cl
NCMe
N
N
Cl
N
N
N
mainly due to dp(Ru) ? p
*(azo) back bonding [26–44,6,45,7,46–
Ru
Ru
Ru
48]. The –N@N– bond length is 1.275–1.279 Å and is longer than
N
N
CO
the free ligand azo distance (1.258 Å) [66–68], which supports
N
CO
the dp(Ru)–p
*(azo) back bonding. Of the Ru–C bond lengths,
CO
Cl
CO
Cl
(Ru(1)–C(1), 1.879(3); Ru(1)–C(2), 1.894(3); Ru(2)–C(14),
1.876(3); Ru(2)–C(15), 1.894(3) Å) the bonds trans to Ru–N(imid-
azole) (Ru(1)–C(1) and Ru(2)–C(14)) are shorter than the bonds
3/4
3''/4''
3'/4'
5/6
Scheme 1.

3022
T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
Table 1
Selected bond distances (Å) and bond angles (°) of (3b), X-ray and theoretical
Molecule-1
Molecule-2
Calculated structure
C(1)–O(1)
C(2)–O(2)
Ru(1)–C(1)
Ru(1)–C(2)
Ru(1)–N(1)
Ru(1)–N(3)
Ru(1)–Cl(4)
Ru(1)–Cl(5)
N(1)–N(2)
1.133(4)
1.116(4)
1.879(3)
1.894(3)
2.132(2)
2.102(2)
2.3798(8)
2.3852(9)
1.279(3)
C(14)–O(3)
C(15)–O(4)
Ru(2)–C(14)
Ru(2)–C(15)
Ru(2)–N(5)
Ru(2)–N(7)
Ru(2)–Cl(3)
Ru(2)–Cl(6)
N(5)–N(6)
1.130(4)
1.113(4)
1.876(3)
1.894(3)
2.123(2)
2.106(2)
2.3823(8)
2.3799(9)
1.275(3)
1.139
1.122
1.884
1.906
2.138
2.112
2.394
2.390
1.288
O(1)–C(1)–Ru(1)
O(2)–C(2)–Ru(1)
C(1)–Ru(1)–C(2)
C(1)–Ru(1)–N(3)
C(2)–Ru(1)–N(3)
C(1)–Ru(1)–N(1)
C(2)–Ru(1)–N(1)
C(1)–Ru(1)–Cl(4)
C(2)–Ru(1)–Cl(4)
C(1)–Ru(1)–Cl(5)
C(2)–Ru(1)–Cl(5)
N(3)–Ru(1)–N(1)
N(1)–Ru(1)–Cl(4)
N(3)–Ru(1)–Cl(4)
N(1)–Ru(1)–Cl(5)
N(3)–Ru(1)–Cl(5)
177.6(3)
177.9(3)
O(3)–C(14)–Ru(2)
O(4)–C(15)–Ru(2)
C(14)–Ru(2)–C(15)
C(14)–Ru(2)–N(7)
C(15)–Ru(2)–N(7)
C(14)–Ru(2)–N(5)
C(15)–Ru(2)–N(5)
C(14)–Ru(2)–Cl(3)
C(15)–Ru(2)–Cl(3)
C(14)–Ru(2)–Cl(6)
C(15)–Ru(2)–Cl(6)
N(7)–Ru(2)–N(5)
N(7)–Ru(2)–Cl(6)
N(5)–Ru(2)–Cl(6)
N(7)–Ru(2)–Cl(3)
N(5)–Ru(2)–Cl(3)
176.0(3)
178.9(3)
178.1
178.2
90.21
174.1
95.06
98.70
170.9
92.42
91.64
89.92
91.80
75.93
89.67
89.88
86.55
87.47
88.34(12)
172.53(12)
98.53(11)
98.13(11)
173.53(11)
93.37(10)
89.77(11)
88.98(10)
91.94(11)
75.13(9)
89.08(14)
171.38(12)
98.51(11)
97.11(11)
173.79(11)
94.00(10)
90.64(11)
89.40(10)
91.44(11)
75.28(9)
87.69(7)
89.61(7)
90.35(7)
87.87(7)
86.35(7)
88.14(7)
90.01(7)
89.43(7)
that are trans to Ru–N(azo) (Ru(1)–C(2) and Ru(2)–C(15)). This is
usual due to a better trans influence of imidazole-N compared to
azo-N donors. The C–O distances (C(1)–O(1), 1.133(4); C(2)–O(2),
1.116(4); C(14)–O(3), 1.130(4); C(15)–O(4), 1.113(4) Å) vary to
within 0.01–0.02 Å. The difference between the two molecules in
the lattice primarily lies in the detail of the conformation. The
pendant phenyl ring is inclined to the mean plane of the chelate
ring, and the angles are molecule-1, 36.73(17); molecule-2,
41.99(15). The torsion angles vary in a characteristic manner.
Examples from those among the atoms of the chelate ring are:
Ru(1)–N(3)–C(9)–N(2): 2.2(4); Ru(2)–N(7)–C(22)–N(6): ꢂ3.3(4);
C(9)–N(2)–N(1)–Ru(1): ꢂ1.3(3); C(22)–N(6)–N(5)–Ru(2): 2.4(3);
N(2)–N(1)–Ru(1)–N(3): 1.8(2); N(6)–N(5)–Ru(2)–N(7): ꢂ3.2(2).
Thus, these two molecules represent a subtle form of conforma-
tional isomerism in a metal chelate, sustained by the crystal lattice.
spectra, we performed TD-DFT calculations of the low lying excita-
tion at the singlet optimized geometry, including the solvation ef-
fect by means of the non-equilibrium implementation of the
polarizable continuum model [74]; as in the experimental condi-
tions, the chosen solvent was acetonitrile. GaussSum [75] was used
to calculate the fractional contributions of various groups to each
molecular orbital. This is done using Mulliken population analysis.
The calculated structure of 3b correlates very well with the re-
sults of its X-ray analysis (Fig. 1, Table 1). The theoretical Ru–N
bond lengths are about 0.010 Å longer than those observed. Simi-
larly the experimental Ru–Cl distances are shorter by 0.015 Å than
the theoretical data. The Ru–C and C–O distances are also reduced
by 0.006–0.010 Å in the experimental data compared to the calcu-
lated structure. The computation of
m(CO) from the DFT calculation
shows a lowering of frequency by 8–10 cmꢂ1
.
Non-covalent interactions, C–Hꢀ ꢀ ꢀ
p
and
p
ꢀ ꢀ ꢀ
p
, exist to provide
The DFT calculation shows a lower energy of the HOMO of
trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b) (EHOMO): ꢂ6.17 eV) than that
of cis-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b0) (EHOMO): ꢂ5.60 eV) and cis-
(Cl)-cis-(CO)-[Ru(CO)2Cl2(PaiEt)] (3b00) (EHOMO): ꢂ5.86 eV). This re-
flects better stability of the trans-(Cl,Cl) than cis-(Cl,Cl) configura-
tion. An interesting feature of the valence orbitals is that the
highest occupied MOs (HOMO, abbreviated as H, H ꢂ 1, H ꢂ 2,
H ꢂ 3) contain >65% and >45% of the Cl atomic functions in 3b
and 5b, respectively. Metal orbitals contribute >20% to H and
H ꢂ 1. The LUMO (abbreviated L) is mostly characterized by the
azoimidazole ligand function (>80%) for both these complexes,
while other unoccupied molecular orbitals have CO >20% and Ru
contribution varies from 5% to 35%. The results in acetonitrile
phase show a significant difference from the gas phase, in particu-
lar to the occupied MOs. In the HOMO the contribution of PaiEt (L)
is 42% in MeCN and 1% in the gas phase, while the Cl contribution is
28% in MeCN and the gas phase contribution is 67% for 3b. The sit-
uation is different for 5b: 14% (gas) and 24% (MeCN). H ꢂ 1 in the
gas and acetonitrile phases remains more or less the same. The
HOMO is stabilized by 0.63 eV in 3b and 0.72 eV in 5b from the
gas to acetonitrile phase. The HOMO is also lowered in energy by
0.54 eV in 3b compared to 5b and the HOMO–LUMO energy gaps
are 3.04 eV for 3b and 2.83 eV for 5b in MeCN (Fig. 3).
rigidity to the supramolecule. An intermolecular hydrogen bond
between one of the coordinated Cl ligands and the H atom of the
ortho C–H of the pendant azophenyl group of an adjacent molecule
constitutes a dimer structure (Fig. 2a). Each dimer interacts with
adjacent dimers via C–Hꢀ ꢀ ꢀ
p
and
p p interactions to generate a
ꢀ ꢀ ꢀ
supramolecular network (Fig. 2b). The interactions are summa-
rized in Table 2.
2.3. DFT and TD-DFT calculations
DFT and TD-DFT calculations were performed for complexes 3b
and 5b. All the calculations were performed using the GAUSSIAN03
(G03) [71] software package, running under Windows. The Becke’s
three-parameter hybrid exchange functional and the Lee–Yang–
Parr non-local correlation functional [72] (B3LYP) was used
throughout. Elements except ruthenium were assigned a 6-31 G*
basis set in our calculations. For ruthenium the Los Alamos effec-
tive core potential plus double zeta (LanL2DZ) [73] basis set was
employed. Gas and solution-phase geometry optimization was car-
ried out. In all cases, vibrational frequencies were calculated to en-
sure that the optimized geometries represented local minima. To
check the effect of solvation on the calculated optical absorption

T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
3023
Fig. 2. (a) C–Hꢀ ꢀ ꢀCl hydrogen bonded dimer unit, (b)
p
ꢀ ꢀ ꢀ
p
and CHꢀ ꢀ ꢀ
p
interacted ab-plane (
p
ꢀ ꢀ ꢀ
p
; C–Hꢀ ꢀ ꢀ
p
in yellow; C–Hꢀ ꢀ ꢀCl in magenta). (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of this article.)
Table 2
Distance of non-covalent interactions in 3b
dC–H (Å)
dHꢀ ꢀ ꢀCl (Å)
dCꢀ ꢀ ꢀCl (Å)
Angle (°)
Symmetry
Hydrogen bonding
C(4)–H(4)ꢀ ꢀ ꢀCl(6)
C(17)–H(17)ꢀ ꢀ ꢀCl(5)
0.930
0.930
2.680
2.660
3.560(4)
3.456(3)
157.0
144.0
ꢂ1 + x, y, z
1 + x, y, z
dHꢀ ꢀ ꢀCg (Å)
dC—Cg (Å)
Angle (°)
Symmetry
C–Hꢀ ꢀ ꢀ
p interaction
C(13)–H(13 C) ? Cg(3)
2.984
3.799(8)
Alpha
143.45
ꢂ1 + x, y, z
Symmetry
dCgꢀ ꢀ ꢀCg (Å)
d (perpendicular)
p p interaction
ꢀ ꢀ ꢀ
Cg(2) ? Cg(5)
3.691(2)
1.02
3.447
x, y, z
Cg(2): N(7)–C(22)–N(8)–C(24)–C(23); Cg(3): C(16)–C(17)–C(18)–C(19)–C(20)–C(21); Cg(5): N(3)–C(9)–N(4)–C(11)–C(10).

3024
T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
Fig. 3. Energy level correlation diagram of 3b and 5b in the gas and acetonitrile phase (top) and HOMO, LUMO picture (bottom).
2.4. Spectra and bonding
quencies, m(C@N), m(N@N), m(CO) and m(Ru–Cl), by the DFT calcula-
tion shows a slightly lower frequency (5–10 cmꢂ1) than that of the
experimental data, but still being within the reported frequency
range.
The infrared spectra of 3 and 4 show the presence
m (CO)
stretching vibrations at 1990–2010 and 2065–2075 cmꢂ1 (Table
3) which indicates the cis coordination of two CO ligands [67–
The electronic spectra of 3 and 4 show an intense broad band at
470–500 nm, and in addition to this the molecules show a more in-
tense and sharp band at 380–400 nm. The lower energy band in the
mono-carbonyl complexes (5 and 6) has been shifted to a longer
wavelength by 15–20 nm compared to the di-carbonyl precursors,
3 and 4 (Fig. 4). Thus, the energy of transition is lowered in 5/6
compared to 3/4. This is well explained on the basis of the DFT cal-
culation using the optimized geometry of a representative com-
plex. The DFT calculations of 3b and 5b show that the HOMO–
LUMO energy gap decreased by 0.21 eV in 5b compared to 3b in
acetonitrile (Fig. 3). The TD-DFT calculations of 3b and 5b show
that the transition at 470–530 nm (Table 5) could be assigned to
H/H ꢂ 1 ? L. H and H ꢂ 1 are localized on parts of the metal and
Cl, and L have major ligand character. Thus, the transition is admix-
70,76–78] (Fig. 1.)
icant peaks appear at 1570–1590 cmꢂ1 and 1350–1370 cmꢂ1
corresponding to (C@N) and (N@N), respectively. The azo
m
(Ru–Cl) appears at 330–340 cmꢂ1. Other signif-
,
m
m
stretching is significantly shifted to the lower frequency region
compared to the free ligand value (1400–1410 cmꢂ1) [79,80],
which supports an efficient back donation, d
The infrared spectra of 5 and 6 show one
1985 cmꢂ1, which is in support of mono-carbonyl formulation,
and the shifting to the lower frequency region compared to (CO)
of 3/4 is an indication of better d (Ru(II)) ?
*(CO) donation in
p(Ru(II)) ?
p
*(azo).
m
(CO) at 1980–
m
p
p
5/6. The Mulliken population analysis of 3b and 5b show that the
positive charge on CO in 5b (0.18619) is less than that of the CO
groups in 3b (0.21986 and 0.23749). Computation of the major fre-

T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
3025
Table 3
FT-IRa, UV–Vis spectralb and cyclic voltammetricc data of the complexes
a
Complex
IR data
m
(CO) (cmꢂ1
)
UV–Vis spectral datab kmax (nm)
Cyclic voltammetric datac
(10ꢂ3 2 Mꢂ1 cmꢂ1
)
ERu(III)/Ru(II), V (
D
Ep, mV)
Ligand reduction, V (
D
Ep, mV)
trans-(Cl)-[Ru(CO)2Cl2(PaiMe)] (3a)
trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b)
trans-(Cl)-[Ru(CO)2Cl2(PaiBz)] (3c)
trans-(Cl)-[Ru(CO)2Cl2(TaiMe)] (4a)
trans-(Cl)-[Ru(CO)2Cl2(TaiEt)] (4b)
trans-(Cl)-[Ru(CO)2Cl2(TaiBz)] (4c)
trans-(Cl)-[Ru(CO)Cl2(PaiMe)(NCMe)] (5a)
trans-(Cl)-[Ru(CO)Cl2(PaiEt)(NCMe)] (5b)
trans-(Cl)-[Ru(CO)Cl2(PaiBz)(NCMe)] (5c)
trans-(Cl)-[Ru(CO)Cl2(TaiMe)(NCMe)] (6a)
trans-(Cl)-[Ru(CO)Cl2(TaiEt)(NCMe)] (6b)
trans-(Cl)-[Ru(CO)Cl2(TaiBz)(NCMe)] (6c)
1995, 2068
2010, 2072
2000, 2070
2000, 2068
2003, 2070
1990, 2068
1975
1980
1970
1972
1982
388(13.76), 500(3.07)
399(12.43), 480(2.88)
390(12.83), 498(3.05)
392(12.84), 498(2.37)
395(13.64), 500(2.82)
390(11.49), 505(2.73)
369(11.28), 540(3.24)
386(12.50), 515(2.92)
382(10.64), 530(4.65)
383(11.34), 530(3.21)
383(10.84), 530(4.68)
378(11.33), 525(2.94)
1.35(130)
1.30(130)
1.40(140)
1.36(140)
1.30(130)
1.35(140)
0.82(110)
0.84(110)
0.85(110)
0.80(110)
0.85(100)
0.87(100)
ꢂ0.46(120), ꢂ1.30(210)
ꢂ0.48(120), ꢂ1.32(210)
ꢂ0.50(120), ꢂ1.30(210)
ꢂ0.48(120), ꢂ1.25(210)
ꢂ0.55(120), ꢂ1.30(210)
ꢂ0.53(120), ꢂ1.35(210)
ꢂ0.53(125), ꢂ1.25(220)
ꢂ0.58(130), ꢂ1.28(220)
ꢂ0.60(120), ꢂ1.26(220)
ꢂ0.57(120), ꢂ1.26(220)
ꢂ0.62(125), ꢂ1.30(220)
ꢂ0.65(120), ꢂ1.27(220)
1968
a
KBr disc.
Solvent, dry acetonitrile.
b
c
Solvent MeCN, Pt-disk working electrode, Ag/AgCl reference electrode, Pt-wire auxiliary electrode, [nBu4N][ClO4] supporting electrolyte. ERu(III)/Ru(II) = 0.5(Epa + Epc), V for
Ep = Epa ꢂ Epc, mV where Epc (cathodic-peak-potential), Epa (anodic-peak-potential).
Ru(III)/Ru(II) couple in unit of V,
D
Fig. 4. Experimental UV–Vis spectra and calculated transitions for 3b (left) and 5b (right) in acetonitrile.
ture of MLCT and XLCT transitions (X = Cl) [81]. Because of the Cl
contribution to H ꢂ n (n = 2, 3, 4, 5) (40–80%), the H ꢂ n ? L tran-
sitions may be attributed to XLCT and contribute to the broadening
of the band. The transitions H/H ꢂ n (n = 1–5) ? L + p (p = 1, 2, 3,
separation (DEp > 100 mV). The nature of the voltammogram does
not change with the scan rate (50–250 mV sꢂ1). The Ru(III)/Ru(II)
potential, ca. 1.35 V, of trans-(Cl)-[Ru(CO)2Cl2(PaiR/TaiR)] (3, 4) is
significantly shifted to ca. 0.85 V for trans-(Cl)-[Ru(CO)Cl2(PaiR/
TaiR)(NCMe)] (5, 6). This may be due to the better electron with-
drawing effect of two CO in 3, 4 than that of one CO in 5, 6. The
DFT calculation in acetonitrile also supports the lower energy of
the HOMO in 3b (ꢂ6.80 eV) compared to that of 5b (ꢂ6.26 eV).
The HOMO is also contributed to by the metal (Ru) orbitals, thus
the redox response is assigned to the Ru(III)/Ru(II) couple.
etc.) may be explained as p(PaiEt) ? p
*(CO), an inter-ligand charge
transfer transition. This transition is also mixed with
p (Pai-
Et) ?
p
*(PaiEt) transitions.
The imidazole protons (4- and 5-H) of the coordinated PaiR or
TaiR in the complexes trans-(Cl)-[Ru(CO)2Cl2(PaiR/TaiR)] (3, 4)
show downfield shifting by 0.3–0.4 ppm compared to the free li-
gand data [75–81] and appear at 7.70–7.85 ppm (4-H) and 7.35–
7.50 (5-H) ppm (Table 4). This supports the strong preference of
the binding of imidazole-N to Ru(II). 1-Me of the coordinated
PaiMe/TaiMe in 3a or 4a is singlet at 4.25–4.30 ppm; 1-CH2–CH3
of coordinated PaiEt or TaiEt in 3b or 4b appears as a quartet at
On scanning in the negative direction (0 to ꢂ2.0 V), two redox
responses are observed. The first response is observed at
>ꢂ0.70 V, and is quasireversible (
the second one appears at <ꢂ1.2 V (
ligand belongs to the -acidic azoimine family and can accommo-
D
Ep P 120 mV) in nature, while
D
Ep P 200 mV). The chelated
p
4.60–4.65 ppm, (J = 8.0 Hz) and
a
triplet 1.70–1.72 ppm
date two electrons centered at the azo group (–N@N–). The reduc-
(J = 7.5 Hz) for –CH2– and –CH3, respectively; 1-CH2–(Ph) in (3c
and 4c) is singlet at 5.80–5.90 ppm. The mono-carbonyl com-
plexes, 5 and 6, in general, show aromatic proton signals at a lower
chemical shift position (d) compare to 3 and 4 (with a difference in
tive responses are assigned to accommodatiꢂon of electronsꢂin the
. . .
. . .
azo dominated function [–N@N–]/[–N N–] and [–N N] /[–N–
•
•
N–]2ꢂ. Ligand reduction of azoimidazole complexes appear at neg-
ative potentials and the present data appear at a less negative va-
lue (ꢂ0.5 to ꢂ0.6 V) than that of trans-[Ru(ligand)2Cl2] (ꢂ0.7 to
ꢂ0.8 V). The DFT data have assigned that the LUMO of the com-
plexes are constituted mainly of the azo group of the ligand
(>80%) and thus the reduction is considered as electron accommo-
dation at the azo dominated orbitals.
chemical shift (Dd) of 0.1–0.3 ppm). This may be due to removal of
the strongly -acidic CO from the Ru(CO)2-motif (3, 4) to prepare
p
the Ru(CO)-motif in 5 and 6. The coordinated MeCN in 5 and 6 ap-
pears as a singlet at 2.07-2.15 ppm for d (CH3).
2.5. Electrochemistry
3. Conclusion
The complexes show a Ru(III)/Ru(II) couple (Table 3, Fig. 5)
when scanned in the potential range 0.0–2.0 V. The response is
quasireversible in nature, as is evident from their peak-to-peak
A series of di-carbonyl complexes of the formulae trans-(Cl)-
[Ru(CO)2Cl2(PaiR or TaiR)] (for PaiR: R = Me (3a), Et (3b), CH2Ph

3026
T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
Table 4
1H NMR spectral data of the complexes in CDCl3 at 298 K
Compound
d, ppm (J, Hz)
4-Ha
5-Ha
7, 11-Hb
8, 10-H
9-H/Me
1-R
CH3CN
3a
3b
3c
4ª
4b
4c
5ª
5b
5c
6a
6b
6c
7.78
7.82
7.84
7.76
7.78
7.78
7.61
7.62
7.65
7.56
7.52
7.48
7.44
7.48
7.50
7.44
7.45
7.47
7.21
7.28
7.31
7.30
7.25
7.22
8.08 (7.5)
8.08 (7.5)
8.10 (7.5)
7.98 (8.0)
8.00 (8.0)
8.05 (8.0)
7.80 (7.5)
7.85 (7.5)
7.83 (7.5)
7.68 (8.0)
7.70 (8.0)
7.80 (8.0)
7.52c
7.52c
7.62c
7.60c
2.50d
2.50d
2.48d
7.42c
7.42c
7.50c
2.50d
2.54d
2.50d
4.27e
7.62c
4.65 (8.0)g, 1.70 (7.5)h
7.60c
5.82f
7.36b (8.0)
7.40b (8.0)
7.42 (7.8)
7.42c
4.30e
4.62 (8.0)g, 1.70 (7.5)h
5.94f
4.20e
2.06
2.07
2.06
2.06
2.07
2.07
7.42c
4.60 (7.5)g, 1.74 (7.5)h
7.50c
5.90f
7.16b (8.0)
7.22b (7.5)
7.22 (8.0)
4.18e
4.60 (7.5)g, 1.75 (7.5)h
5.85f
a
Broad singlet.
b
c
d
e
f
Doublet.
Multiplet.
d(Ar-Me).
d(N(1)–Me).
d(N(1)–CH2–Ph).
g
h
d(–CH2–CH3) quartet for –CH2–.
Triplet for –CH3.
Table 5
Selected list of calculated data from TD-DFT excitation energies for 3b and 5b in acetonitrile
Excited state
k, nm(f ꢃ 103)
Major contribution
Compound 3b
1
2
3
5
7
551.8(10.9)
512.8(19.2)
435.8(358.3)
415(93.7)
(79%)HOMO ? LUMO (MLCT, IL), (14%)H ꢂ 2 ? LUMO (IL)
(86%)H ꢂ 1 ? LUMO (MLCT, IL), (10%)H ꢂ 2 ? LUMO (IL)
(49%)H ꢂ 2 ? LUMO, (18%)H ꢂ 4 ? LUMO (IL)
(67%)H ꢂ 3 ? LUMO, (10%)H ꢂ 2 ? LUMO, (10%)H ꢂ 4 ? LUMO] (IL)
(65%)H ꢂ 4 ? LUMO, (19%)H ꢂ 3 ? LUMO] (IL)
394.7(66.2)
Compound 5b
2
4
5
6
528.7(61.2)
436.7(95.3)
404.2(119.8)
400.4(211.0)
(70%)H ꢂ 1 ? LUMO, (19%)HOMO ? LUMO (MLCT, IL)
(33%)H ꢂ 2 ? LUMO, (32%)H ꢂ 3 ? LUMO, (17%) H ꢂ 4 ? LUMO (IL)
(64%)H ꢂ 1 ? L + 1, (MLCT, IL), (18%)H ꢂ 2 ? LUMO (IL)
(28%)H ꢂ 2 ? LUMO, (20%)H ꢂ 3 ? LUMO, (16%)H ꢂ 4 ? LUMO (IL), (16%)H ꢂ 1 ? L + 1 (MLCT, IL)
4. Experimental
4.1. Materials
1-Alkyl-2-(phenylazo)imidazole (1) and 1-alkyl-2-(p-toly-
lazo)imidazole (2) were synthesized following a previously pub-
lished procedure [75–81]. [Ru(CO)2Cl2]n was also prepared by the
reported method [63,64,76–78]. Imidazole and all other organic
chemicals and inorganic salts were available from Sisco Research
Lab., Mumbai, India. The purification of acetonitrile and prepara-
tion of n-tetrabutylammonium perchlorate [nBu4N][ClO4] for elec-
trochemical work were done as reported before [75–81].
Fig. 5. Cyclic voltammogram of (3b) (—) and (5b) (–––) in MeCN using Pt-disk
working and Pt-wire auxiliary electrodes and referenced to the Ag/AgCl electrode.
Dinitrogen was purified by bubbling through an alkaline pyrogallol
solution. All other chemicals and solvents were of reagent grade
and were used without further purification.
(3c); for TaiR: R = Me (4a), Et (4b), CH2Ph (4c)) has been synthe-
sized by reacting [Ru(CO)2Cl2]n with PaiR or TaiR. The complexes
are selectively decarbonylated to isolate trans-(Cl)-[Ru(CO)Cl2(PaiR
or TaiR)(NCMe)] (5/6). However, complete decarbonylation, either
by thermal or photochemical methods, has not been possible. The
complexes are characterized by spectroscopic data and in one case
by an X-ray structure. The computational (DFT) study has dis-
cussed the separation of a single isomer on the basis of energy cal-
culation. The electronic structures support metal centered
oxidations, and reductions of the chelated ligand.
4.2. Physical measurements
Microanalytical data (C, H, N) were collected on Perkin–Elmer
2400 CHNS/O elemental analyzer. Spectroscopic data were ob-
tained using the following instruments: UV–Vis spectra, Perkin–El-
mer, model Lambda 25; IR spectra (KBr disk, 4000–200 cmꢂ1),
Perkin–Elmer, model RX-1; 1H NMR spectra, Bruker (AC)
300 MHz FTNMR spectrometer. Electrochemical measurements
were performed using a computer-controlled PAR model 250 Vers-
aStat electrochemical instrument with a Pt-disk electrode. All

T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
3027
Table 6
Summarised crystallographic data for trans-(Cl)-[Ru(CO)2Cl2(PaiEt)](3b)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C13H12Cl2N4O2Ru
428.24
monoclinic
P21/c
10.6772(14)
14.1537(18)
23.074(3)
107.173(5)
0.42 ꢃ 0.19 ꢃ 0.13
3331.5(7)
0.71073
1.708
b (Å)
c (Å)
b (°)
Size (mm3)
V(Å3)
k (Å)
qcalcd (Mg mꢂ3
)
Z
8
T (K)
298(2)
1.272
l(Mo K
a
) (mmꢂ1
)
Total reflection collected
19700
Unique reflections
6522
Refined parameters
399
Largest difference in peak and hole (e Åꢂ3
)
0.604 and ꢂ0.242
Ra (I > 2
r(I))
0.0330
wRb
0.0809
1.034
Goodness-of-fitc
P
P
a
R = ||Fo | ꢂ|Fc||/ |Fo|.
P
P
2
2
1=2
2
wR ¼ ½ wðF2o ꢂ Fc2Þ = wðFo2Þ ꢁ ; w ¼ 1=½s2ðFo2Þ þ ð0:0417PÞ þ 1:1071Pꢁ; where P ¼ ðFo2 þ 2F2c Þ /3.
b
c
GOF (Goodness of fit) = [w(Fo ꢂ Fc)/(no ꢂ nv)]1/2, where no and nv denote the number of data and variable.
measurements were carried out under a dinitrogen environment at
16.39%. Calc. for C14H15N5OCl2Ru (5b): C, 38.09; H, 3.40; N,
15.87. Found: C, 38.00; H, 3.32; N, 15.83%. Calc. for C19H17N5O2Cl2-
Ru (5c): C, 45.33; H, 3.38; N, 13.92. Found: C, 45.22; H, 3.30; N,
13.98%. Calc. for C14H15N5OCl2Ru (6a): C, 38.09; H, 3.40; N, 15.87.
Found: C, 38.18; H, 3.46; N, 15.82%. Calc. for C15H17N5OCl2Ru
(6b): C, 39.56; H, 3.74; N, 15.38. Found: C, 39.44; H, 3.67; N,
15.30%. Calc. for C20H19N5OCl2Ru (6c): C, 46.42; H, 3.67; N, 13.54.
Found: C, 46.33; H, 3.64; N, 13.48%.
298 K with reference to Ag/AgCl in acetonitrile using [nBu4N][ClO4]
as a supporting electrolyte. The reported potentials are uncor-
rected for junction potentials.
4.3. Synthesis of trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b)
[Ru(CO)2Cl2]n (0.31 g, 1.4 mmol) was dissolved in hot methanol
(30 ml). A methanolic solution of PaiEt (0.28 g, 1.4 mmol) was
added and the solution was refluxed for 2 h under a dinitrogen
atmosphere. The color of the solution changed from orange-red
to brown. Under slow evaporation of the solvent, a brown crystal-
line product was left. The product was further purified from
CH2Cl2–MeOH solution. The yield was 0.34 g (58%).
The other complexes were prepared following an identical pro-
cedure. The yield varied from 50% to 60%. Microanalytical data:
Calc. for C12H10N4O2Cl2Ru (3a): C, 34.78; H, 2.41; N, 13.53. Found:
C, 34.62; H, 2.38; N, 13.47%. Calc. for C13H12N4O2Cl2Ru (3b): C,
36.45; H, 2.80; N, 13.08. Found: C, 36.50; H, 2.81; N, 13.00%. Calc.
for C18H14N4O2Cl2Ru (3c): C, 44.08; H, 2.86; N, 11.43. Found: C,
43.92; H, 2.81; N, 11.38%. Calc. for C13H12N4O2Cl2Ru (4a): C,
36.45; H, 2.80; N, 13.08. Found: C, 36.34; H, 2.78; N, 13.04%. Calc.
for C14H14N4O2Cl2Ru (4b): C, 38.01; H, 3.17; N, 12.67. Found: C,
37.92; H, 3.23; N, 12.60%. Calc. for C19H16N4O2Cl2Ru (4c): C,
45.24; H, 3.17; N, 11.11. Found: C, 45.02; H, 3.21; N, 11.17%.
4.5. X-ray crystal structure determination
Crystals of trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b) were grown by
slow diffusion of a CH2Cl2 solution of the complex into hexane.
The prismatic red crystal used was of dimensions
0.13 ꢃ 0.19 ꢃ 0.42 mm. Diffraction data were collected with a Bru-
ker SMART 1 K CCD area-detector diffractometer using fine focused
sealed tube graphite-monochromatized Mo Ka radiation
(k = 0.7107 Å). A summary of the crystallographic data and struc-
ture refinement parameters are given in Table 6. Data were cor-
rected for Lorentz and polarization effects. Data reduction was
carried out using the ‘Bruker SAINT’ program. The structure was
solved by direct methods using SHELXS-97 [82] and successive differ-
ence Fourier syntheses. All non-hydrogen atoms were refined
2
anisotropically. Full matrix least squares refinements on F0 were
carried out using SHELXL-97 [83] with anisotropic displacement
parameters for all non-hydrogen atoms. Hydrogen atoms were
constrained to ride on the respective carbon or nitrogen atoms
with isotropic displacement parameters equal to 1.2 times the
equivalent isotropic displacement of their parent atom in all cases.
All calculations were carried out using SHELXS 97 [82] and PLATON 99
[84] programs.
4.4. Synthesis of trans-(Cl)-[Ru(CO)Cl2(PaiEt)(NCMe)] (5b)
trans-(Cl)-[Ru(CO)2Cl2(PaiEt)] (3b) (0.1 g, 0.24 mmol) was dis-
solved in dry MeCN and sublimed Me3NO (0.025 g, 0.33 mmol)
was added as a pinch under a dry N2 environment. The solution
was then refluxed for 2 h. The intensity of the bright brown solu-
tion was reduced to light brown. The solution was evaporated
slowly in air while crystals were deposited on the wall of the bea-
ker. They were collected and dried over a CaCl2 desiccator. These
crystals were unstable to X-ray irradiation and we could not per-
form X-ray diffraction analysis. The yield was 0.087 g (84%).
The other complexes were prepared following an identical pro-
cedure. The yield varied from 80% to 90%. Calc. for C13H13N5OCl2Ru
(5a): C, 36.38; H, 2.97; N, 16.30. Found: C, 36.53; H, 3.04; N,
5. Supplementary data
CCDC 645194 contains the supplementary crystallographic data
for [Ru(CO)2Cl2(PaiEt)] (3b). 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,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.

3028
T.K. Mondal et al. / Polyhedron 27 (2008) 3020–3028
[43] S. Goswami, R.N. Mukherjee, A. Chakravorty, Inorg. Chem. 22 (1983)
Acknowledgements
2825.
[44] P. Ghosh, A. Chakravorty, J. Chem. Soc., Dalton Trans. (1985) 361.
[45] G.K. Lahiri, S. Bhattacharya, S. Goswami, A. Chakravorty, J. Chem. Soc., Dalton
Trans. (1990) 561.
[46] G.K. Lahiri, S. Goswami, L.R. Falvello, A. Chakravorty, Inorg. Chem. 26 (1987)
3365.
Financial support from DST and UGC, New Delhi are thankfully
acknowledged. We thank Dr. A.D. Jana for crystallographic
graphics.
[47] R. Samanta, P. Munshi, B.K. Santra, N.K. Loknath, M.A. Sridhar, J.S. Prasad, G.K.
Lahiri, J. Org. Met. Chem. 579 (1999) 311.
[48] R.A. Krause, K. Krause, Inorg. Chem. 19 (1980) 2600. 1982 (21) 1714; 1984 (23)
219.
References
[49] A. Bharat, B.K. Santra, P. Munshi, G.K. Lahiri, J. Chem. Soc., Dalton Trans. (1998)
2643.
[50] A. Seal, S. Roy, Acta Crystallogr., Sect C C40 (1984) 929.
[51] A.H. Velders, H. Kooijman, A.L. Spek, J.G. Haasnoot, D. de Vos, J. Reedijk, Inorg.
Chem. 39 (2000) 2966.
[1] J. Reedijk, in: G. Willkinson, J.A. Mccleverty (Eds.), Comprehensive
Coordination Chemistry, vol. 2, Pergamon, Oxford, UK, 1987, p. 430.
[2] W.T. Wong, Coord. Chem. Rev. 131 (1994) 45.
[3] G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive Organometallic
Chemistry, Pergamon Press, New York, 1982.
[52] A.C.G. Hotze, A.H. Velders, F. Ugozzoli, M. Bicingi, A.M. Manotti-Lanfredi, J.G.
Haasnoot, J. Reedijk, Inorg. Chem. 39 (2000) 3838.
[4] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley-
Intersciences, New York, 1994.
[53] M. Shivakumar, K. Pramanik, P. Ghosh, A. Chakravorty, Chem. Commun. (1998)
2103.
[54] K.S.Y. Leung, Y. Li, Inorg. Chem. Commun. 2 (1999) 599.
[55] W.Y. Wong, S.H. Cheung, S.M. Lee, S.Y. Leung, J. Org. Chem. 596 (2000) 36.
[56] K. Pramanik, M. Shivakumar, P. Ghosh, A. Chakravorty, Inorg. Chem. 39 (2000)
195.
[57] V.W.W. Yam, V.C.Y. Lan, L.X. Wu, J. Chem. Soc., Dalton Trans. (1998) 1461.
[58] R. Samanta, P. Munshi, B.K. Santra, N.K. Loknath, M.A. Sridhar, J.S. Prasad, G.K.
Lahiri, J. Organomet. Chem. 579 (1999) 311.
[59] G. Cripps, A. Pellissier, S. Chardon-Noblat, A. Deronzier, R.J. Haines, J.
Organomet. Chem. 689 (2004) 484.
[5] K. Kalyansundaram, Coord. Chem. Rev. 46 (1982) 159.
[6] B.K. Ghosh, A. Chakravorty, Coord. Chem. Rev. 95 (1989) 239.
[7] N. Bag, A. Pramanik, G.K. Lahiri, A. Chakravorty, Inorg. Chem. 31 (1992) 40.
[8] S. Serroni, S. Campagna, F. Puntoriero, C.D. Pietro, N.D. Mcclenaghan, F. Loisean,
Chem. Soc. Rev. 30 (2001) 367.
[9] A.C.G. Hotze, H. Kooijman, A.L. Spek, J.G. Haasnoot, J. Reedijk, New J. Chem. 28
(2004) 565.
[10] R.E. Shepherd, Coord. Chem. Rev. 247 (2002) 147.
[11] M.J. Overett, J.R. Moss, Inorg. Chim. Acta 358 (2005) 1715.
[12] S.J. Dougan, M. Melchart, A. Habtemariam, S. Parsons, P.J. Sadler, Inorg. Chem.
45 (2006) 10882.
[60] S. Chardon-Noblat, A. Deronzier, R. Ziessel, D. Zsoldos, J. Electroanal. Chem. 444
(1998) 253.
[13] C.K. Pal, S. Chattopadhyay, C. Sinha, D. Bandhyopadhyay, A. Chakravorty,
Polyhedron 13 (1994) 999.
[61] J.-M. Lehn, R. Ziessel, J. Organomet. Chem. 382 (1990) 157.
[62] S. Chardon-Noblat, A. Deronzier, R. Ziessel, Collect. Czech. Chem. Commun. 66
(2001) 207.
[14] P.K. Santra, R. Roy, C. Sinha, Proc. Indian Acad. Sci. (Chem. Sci.) 112 (2000) 523.
[15] B.K. Santra, P. Munshi, G. Das, P. Bharadwaj, G.K. Lahiri, Polyhedron 18 (1999)
617.
[63] J.M. Kelly, C.M. O_Connell, J.G. Vos, Inorg. Chim. Acta 64 (1982) L75.
[64] S. Chardon-Noblat, P. Da Costa, A. Deronzier, M. Haukka, T.A. Pakkanen, R.
Ziessel, J. Electroanal. Chem. 490 (2000) 62.
[65] H. Sigel (Ed.), Metal Ions in Biological System, vol. 13, Marcel Dekker, New
York, 1981.
[66] J. Otsuki, K. Suwa, K. Narutaki, C. Sinha, I. Yoshikawa, K. Araki, J. Phys. Chem. A
109 (2005) 8064.
[67] J. Otsuki, K. Suwa, K.K. Sarker, C. Sinha, J. Phys. Chem. A 111 (8) (2007)
1403.
[68] P. Bhunia, B. Baruri, U.S. Ray, C. Sinha, S. Das, J. Cheng, T.-H. Lu, Transition Met.
Chem. 31 (2006) 310.
[69] E.Y. Li, Y.-M. Cheng, C.-C. Hsu, P.-T. Chou, G.-S. Lee, I.-H. Lin, Y. Chi, C.-S. Liu,
Inorg. Chem. 45 (2006) 8041.
[70] E. Eskelinen, M. Haukka, T. Venalainen, T.A. Pakkanen, M. Wasberg, S. Chardon-
Noblat, A. Deronzier, Organometallics 19 (2000) 163.
[71] M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.M.W. Gill, B.G. Johnson, M.A. Robb, J.R.
Cheeseman, T.A. Keith, G.A. Petersson, J.A. Montgomery, K. Raghavachari, M.A.
Al-Laham, V.G. Zakrzewski, J.V. Ortiz, J.B. Foresman, J. Cioslowski, B.B. Stefanov,
A. Nanayakkara, M. Challacombe, C.Y. Peng, P.Y. Ayala, W. Chen, M.W. Wong,
J.L. Andres, E.S. Replogle, R. Gomperts, R.L. Martin, D.J. Fox, J.S. Binkley, D.J.
Defrees, J. Baker, J.P. Stewart, M. Head-Gordon, C. Gonzalez, J.A. Pople,
GAUSSIAN98, Gaussian, Inc., Pittsburgh, PA, 1998.
[16] P.K. Santra, P. Byabratta, S. Chattopadhyay, C. Sinha, L.R. Falvello, Eur. J. Inorg.
Chem. (2002) 1124.
[17] M. Panda, S. Das, G. Mostafa, A. Castineiras, S. Goswami, J Chem. Soc., Dalton
Trans. (2005) 1249.
[18] U.S. Ray, B.K. Ghosh, M. Monfort, J. Ribas, G. Mostafa, T.-H. Lu, C. Sinha, Eur. J.
Inorg. Chem. (2004) 250.
[19] U.S. Ray, B.G. Chand, G. Mostafa, J. Cheng, T.-H. Lu, C. Sinha, Polyhedron 22
(2003) 2587.
[20] D. Banerjee, U.S. Ray, J.-C. Liou, C.-N. Lin, T.-H. Lu, C. Sinha, Inorg. Chim. Acta
358 (2005) 1019.
[21] U.S. Ray, D. Banerjee, B.G. Chand, J. Cheng, T. –H. Lu, C. Sinha, J. Coord. Chem. 58
(2005) 1105.
[22] B.G. Chand, U.S. Ray, J. Cheng, T.-H. Lu, C. Sinha, Polyhedron 22 (2003) 1213.
[23] B.G. Chand, U.S. Ray, G. Mostafa, T.-H. Lu, C. Sinha, Polyhedron 23 (2004) 1669.
[24] B.G. Chand, U.S. Ray, G. Mostafa, T.-H. Lu, C. Sinha, J. Coord. Chem. 57 (2004) 627.
[25] B.G. Chand, U.S. Ray, J. Cheng, T.-H. Lu, C. Sinha, Inorg. Chim. Acta 358 (2005)
1927.
[26] T.K. Misra, D. Das, C. Sinha, P.K. Ghosh, C.K. Pal, Inorg. Chem. 37 (1998) 1672.
[27] T.K. Misra, D. Das, C. Sinha, Polyhedron 16 (1997) 4163.
[28] T.K. Misra, D. Das, C. Sinha, Indian J. Chem. A 37 (1998) 741.
[29] S. Pal, T.K. Misra, P. Chattopadhyay, C. Sinha, Proc. Indian Acad. Sci. (Chem. Sci.)
111 (1999) 687.
[72] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[73] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270.
[74] M. Cossi, V.J. Barone, Chem. Phys. 115 (2001) 4708.
[75] N.M. O’Boyle, J.G. Vos, GaussSum 1.0, Dublin City University, Dublin, Ireland,
2005. <http://www.gausssum.sourceforge.net>.
[76] M.I. Bruce, Ruthenium carbonyls and related compounds, in: G. Wilkinson,
F.G.A. Stone, E.W. Abel (Eds.), Comprehensive Organometallic Chemistry, vol.
4, Pergamon Press, Oxford, 1982, p. 661.
[30] M.N. Ackermann, C.R. Barton, C.J. Deodene, E.M. Specht, S.C. Keill, W.E.
Schreiber, Hiodong. Kim, Inorg. Chem. 28 (1989) 397.
[31] F. Alper, C. Kayram, S. Ozkar, J. Organomet. Chem. 691 (2006) 2734.
[32] W. Kaim, S. Ernst, S. Kohlmann, Polyhedron 5 (1986) 295.
[33] W. Kaim, S. Kohlmann, Inorg. Chem. 25 (1986) 3442.
[34] W. Kaim, S. Kohlmann, Inorg. Chem. 26 (1987) 68.
[35] M.N. Ackermann, W.G. Fairbrother, N.S. Amin, C.J. Deodene, C.M. Lamborg, P.T.
Martin, J. Organomet. Chem. 523 (1996) 145.
[77] A.J. Deeming, C. Forth, G. Hogarth, Transition Met. Chem. 31 (2006) 42.
[78] M. Haukka, J. Kiviaho, M. Ahlgren, T.A. Pakkam, Organometallics 14 (1995)
825.
[79] J. Dinda, Ph.D. Thesis, The University of Burdwan, Burdwan, India, 2003.
[80] J. Dinda, K. Bag, C. Sinha, G. Mostafa, T.-H. Lu, Polyhedron 22 (2003) 1367.
[81] A. Gabrielsson, S. Zalis, P. Matousek, M. Towrie, A. Vlcek Jr., Inorg. Chem. 43
(2004) 7380.
[36] M.J. Alder, W.I. Cross, K.R. Flower, R.G. Pritchard, J. Organomet. Chem. 568
(1998) 279.
[37] M.N. Ackermann, S.R. Kiihne, P.A. Saunders, C.E. Barnes, S.C. Stalling, H. Kim, C.
Woods, M. Lagunoff, Inorg. Chim. Acta 334 (2002) 193.
[38] M.N. Ackermann, M.P. Robinson, I.A. Maher, E.B. LeBlane, R.V. Raz, J.
Organomet. Chem. 682 (2003) 248.
[39] P. Datta, P. Gayen, C. Sinha, Polyhedron 25 (2006) 3435.
[40] M.A. Moreno, M. Haukka, A. Turunen, T.A. Pakkanen, J. Mol. Catal. A: Chem. 240
(2005) 7.
[82] G.M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structure,
University of Gottingen, Germany, 1997.
[83] G.M. Sheldrick, SHELXL-97, Program for the Solution of Crystal Structure,
University of Gottingen, Germany, 1997.
[41] E.A. Seddon, K.R. Seddon, The Chemistry of Ruthenium;, Elsevier, Amsterdam,
1984.
[84] A.L. Spek, PLATON, Molecular Geometry Program, University of Utrecht, The
Netherlands, 1999.
[42] S. Goswami, A.R. Chakravarty, A. Chakravorty, Inorg. Chem. 20 (1981) 2246. 21
(1982) 2173; 22 (1983) 602.