Chemistry of 2-(phenylazo)pyridine complexes of osmium: Synthesis, characterization and reactivities

Article abstract of DOI:10.1016/S0277-5387(00)00378-8

Reaction of 2-(phenylazo)pyridine (pap) with [Os(PPh₃)₃Br₂] afforded a mixed ligand complex of the type [Os(PPh₃)₂(pap)Br₂]. The structure of this complex was determined by X-ray crystallography. The PPh₃ ligands are trans and the bromides are in cis positions. The pap ligand is coordinated to osmium as a bidentate N,N-donor forming a five-membered chelate ring. The complex is diamagnetic (low-spin d⁶, S=0) and in dichloromethane solution shows intense MLCT transitions in the visible region. The two bromides were replaced from the coordination sphere of [Os(PPh₃)₂(pap)Br₂] under mild conditions by a series of anionic ligands L (where L=quinolin-8-olate (q), picolinate (pic), oxalate (Hox), 1-nitroso-2-naphtholate (nn) and acetyl acetonate (acac)) to afford complexes of the type [Os(PPh₃)₂(pap) (L)]⁺, which were isolated and characterized as the perchlorate salt. The structure of the [Os(PPh₃)₂(pap) (acac)]ClO₄ complex was determined by X-ray crystallography. The PPh₃ ligands occupy trans positions and the acetylacetonate anion is coordinated to osmium as a bidentate O,O-donor forming a six-membered chelate ring. The [Os(PPh₃)₂(pap) (L)]⁺ complexes are diamagnetic and show multiple MLCT transitions in the visible region. [Os(PPh₃)₂(pap)Br₂] shows an osmium(II)-osmium(III) oxidation at 0.49 V versus SCE. The same oxidation is displayed by the [Os(PPh₃)₂(pap) (L)]⁺ complexes within 0.69 to 0.96 V versus SCE. Two successive one-electron reductions of the coordinated pap ligand are also observed in all the complexes below -0.90 V versus SCE. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00378-8

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1227–1232
Chemistry of 2-(phenylazo)pyridine complexes of osmium:
synthesis, characterization and reactivities
Anindya Das a, Shie-Ming Peng b, Samaresh Bhattacharya a,
*
a Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Calcutta 700032, India
b Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROC
Received 5 January 2000; accepted 24 February 2000
Abstract
Reaction of 2-(phenylazo)pyridine (pap) with [Os(PPh3)3Br2] afforded a mixed ligand complex of the type [Os(PPh3)2(pap)Br2]. The
structure of this complex was determined by X-ray crystallography. The PPh3 ligands are trans and the bromides are in cis positions. The pap
ligand is coordinated to osmium as a bidentate N,N-donor forming a five-membered chelate ring. The complex is diamagnetic (low-spin d6,
Ss0) and in dichloromethane solution shows intense MLCT transitions in the visible region. The two bromides were replaced from the
coordination sphere of [Os(PPh3)2(pap)Br2] under mild conditions by a series of anionic ligands L (where Lsquinolin-8-olate (q),
picolinate (pic), oxalate (Hox), 1-nitroso-2-naphtholate (nn) and acetyl acetonate (acac)) to afford complexes of the type
[Os(PPh3)2(pap)(L)]q, which were isolated and characterized as the perchlorate salt. The structure of the [Os(PPh3)2(pap)(acac)]ClO4
complex was determined by X-ray crystallography. The PPh3 ligands occupy trans positions and the acetylacetonate anion is coordinated to
osmium as a bidentate O,O-donor forming a six-membered chelate ring. The [Os(PPh3)2(pap)(L)]q complexes are diamagnetic and show
multiple MLCT transitions in the visible region. [Os(PPh3)2(pap)Br2] shows an osmium(II)–osmium(III) oxidation at 0.49 V versus SCE.
The same oxidation is displayed by the [Os(PPh3)2(pap)(L)]q complexes within 0.69 to 0.96 V versus SCE. Two successive one-electron
reductions of the coordinated pap ligand are also observed in all the complexes below y0.90 V versus SCE.
Ltd All rights reserved.
q2000 Elsevier Science
Keywords: Osmium; Triphenylphosphine; 2-(Phenylazo)pyridine; Synthesis; Structures; Reactivities
1. Introduction
in this OsBr2 moiety, two p-acid ligands, i.e. 2-(phenyl-
azo)pyridine (pap, 1) and triphenylphosphine (PPh3), have
The chemistry of osmium has been receiving considerable
attention [1–18], largely because of the variety ofreactivities
exhibited by its complexes. Most of these reactions require
directcontactof thereactantwiththemetalcenter.Asosmium
is usually coordinatively saturated in its complexes, such
direct links can only be established via dissociation of rela-
tively weak metal–ligand bonds. Osmium complexes having
potentially labile ligands are of particular importance in this
regard. In the present work, which has emerged from our
interest in the chemistry of osmium in different coordination
environments [19–23], we have chosen an OsBr2 moiety as
the reactive fragment, because the Os–Br bonds are known
to undergo dissociation under rathermildconditions[24,25].
To satisfy the remaining four coordination sites of osmium
been utilized. 2-(Phenylazo)pyridine is well known for its
strong p-acidity [26–28], by virtue of which it stabilizes the
lower oxidation states of a metal. Triphenylphosphine also
favors the lower oxidation states of a metal via dp–dp inter-
action. Coordination by these p-acid ligands has been
planned in order to stabilize the bivalent state of osmium,
which in turn is expected to favor dissociation of the Os–Br
bonds. The targeted complex, [Os(PPh3)2(pap)Br2], has
been synthesized and the reactivity of the OsBr2 fragment
towards displacement by a group of bidentate ligands (L) of
different types has been studied. An account of the chemistry
of [Os(PPh3)2(pap)Br2] and [Os(PPh3)2(pap)(L)]q
complexes is reported here with special reference to synthe-
sis, structure and redox properties.
* Corresponding author. Tel.: q91-33-483-8393; fax: q91-33-473-4266;
e-mail: samaresh b@hotmail.com
–
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(00)00378-8
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2. Experimental
2.1. Materials
In the case of HLsHq and Hnn, 2-methoxyethanol was
used as solvent instead of ethanol and triethanolamine was
used as base instead of triethylamine.
Osmium tetroxide was purchased from Arora Matthey,
Calcutta, India and was converted into [NH4]2[OsBr6] by
reduction with HBr [29]. [Os(PPh3)3Br2] was synthesized
from [NH4]2[OsBr6] using a literature method [30]. Tri-
phenylphosphine, acetylacetone (Hacac), oxalic acid
(H2ox) and 1-nitroso-2-naphthol (Hnn) were purchased
from Loba Chemie, Mumbai, India. Picolinic acid (Hpic)
and quinoline-8-ol (Hq) were purchased from E. Merck
(India). 2-(Phenylazo) pyridine was prepared by following
a literature procedure [31]. All other chemicals and solvents
were reagent grade commercial materials and were used as
received. Purification of acetonitrile and dichloromethane,
and preparation of tetrabutylammoniumperchlorate(TBAP)
for electrochemical work were performed as reported in the
literature [32,33].
2.3. Physical measurements
Microanalyses (C, H, N) were performed using a Perkin-
Elmer 240C elemental analyzer. Infrared spectra were
obtained on a Perkin-Elmer 783 spectrometer with samples
prepared as KBr pellets. Electronic spectra were recorded on
a Shimadzu UV 1601 spectrophotometer. Magnetic suscep-
tibilities were measured using a PAR 155 vibrating sample
magnetometer fitted with a WalkerScientificL75FBALmag-
1
net. H NMR spectra were obtained on a Bruker AC-200
NMR spectrometer using TMS as the internal standard. Solu-
tion electrical conductivities were measured using a Philips
PR 9500 bridge with a solute concentration of 10y3 M. Elec-
trochemical measurements were made using a PAR model
273 potentiostat. A platinum disk or graphite working elec-
trode, a platinum wire auxiliary electrode and an aqueous
saturated calomel reference electrode (SCE) were used in a
three-electrode configuration. A RE 0089 X-Y recorder was
used to trace the voltammograms. Dinitrogengaswaspurified
by successively bubbling it through alkaline dithionite and
concentrated sulfuric acid and all electrochemical measure-
ments were performed under this dinitrogen atmosphere. All
electrochemical data were collected at 298 K and are uncor-
rected for junction potentials.
2.2. Preparation of the complexes
2.2.1. [Os(PPh3)2(pap)Br2]
To a mixture of [Os(PPh3)3Br2] (100 mg, 0.09 mmol)
and 2-(phenylazo)pyridine (16 mg, 0.09 mmol), 2-meth-
oxyethanol (30 cm3) was added. The resulting mixture was
refluxed for 2 h. A red crystalline precipitate started to sep-
arate during reflux. After cooling the solution to room tem-
perature, the precipitate was collected by filtration, washed
thoroughly with ethanol and dried in air. The yield was 52
mg (56%).
2.4. Crystallography
2.2.2. [OsII(PPh3)2(pap)(L)]ClO4 (Lspic, q, Hox, nn,
acac) complexes
The [OsII(PPh3)2(pap)(L)]ClO4 (Lspic, q, Hox, nn,
acac) complexes were synthesized usingageneralprocedure.
Yields varied in the range of 60–65%. Specific details are
given for one complex.
Single crystals of [Os(PPh3)2(pap)Br2] were obtained
directly from the synthetic reaction carried out in 2-meth-
oxyethanol. Selected crystal data and data collection para-
meters are given in Table 1. Data were collected on a Siemens
Smart CCD diffractometer using graphite-monochromated
[Os(PPh3)2(pap)(acac)]ClO4. [Os(PPh3)2(pap)Br2]
(100 mg, 0.10 mmol) was dissolved in dichloromethane (20
cm3) and to this solution was added acetylacetone (10 mg,
0.10 mmol) followed by ethanol (30 cm3) and triethylamine
(10 mg, 0.10 mmol). The solution was boiled for a few
minutes in air to remove dichloromethaneasmuchaspossible
and then it was heated at reflux for 48 h. After being cooled
to room temperature, a saturated aqueous solution of NaClO4
(0.5 cm3) was added to it. [Os(PPh3)2(pap)(acac)]ClO4
precipitated as a red solid and was collected by filtration,
washed with ice-cold water and dried in vacuo over P4O10.
Purification of the product was done by thin layer chroma-
tography on a silica-gel plate, using 1:1 benzene–acetonitrile
as the eluant. A red band separated and was extracted with
acetonitrile. On evaporation of the acetonitrile solution,
[Os(PPh3)2(pap)(acac)]ClO4 was obtained as a red micro-
crystalline solid. The yield was 64 mg (61%).
˚
Mo Ka radiation (ls0.71073 A) by frame using v scans
within the angular range 1.488-u-26.378. X-raydatareduc-
tion and structure solution and refinement were done using
the SHELXTL package. The structure was solved by direct
methods.
Single crystals of [Os(PPh3)2(pap)(acac)]ClO4 were
grown by slow diffusion of hexane into a dichloromethane
solution of the complex. Selected crystal data and data col-
lection parameters are given in Table 1. Data were collected
on a Siemens Smart CCD diffractometer using graphite-
˚
monochromated Mo Ka radiation (ls0.71073 A) by frame
using v scans within the angular range 1.578-u-26.378. X-
ray data reduction and structure solution and refinement were
done using the SHELXTL package. The structure was solved
by direct methods.
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Table 1
Crystallographic data for [Os(PPh3)2(pap)Br2] and [Os(PPh3)2-
(pap)(acac)]ClO4
Formula
FW
C47H39Br2N3P2Os
1057.77
C52H46ClN3O6P2Os
1096.51
Space group
monoclinic, P21/c
10.1561(2)
17.3501(2)
22.8526(3)
90
97.624(1)
90
3991.24(11)
4
monoclinic, P21/n
14.3739(1)
15.2881(1)
22.2380(1)
90
99.894(1)
90
4814.11(5)
4
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
V (A )
Z
rcalc (g cmy3
)
1.760
0.71073
1.513
0.71073
˚
l (A)
Crystal size (mm)
T (K)
0.18=0.08=0.03
295(2)
5.316
0.0503
0.0793
0.80=0.12=0.10
295(2)
2.823
0.0322
0.0664
m (mmy1
)
a
R1
b
wR2
GOF on F2 c
1.078
1.093
a R1s8NNFoNNyNNFcNN/8NFoN.
2
2
b wR2s[8[w(Fo yFc )2]/8[w(Fo2)2]]1/2
.
c GOFs[8[w(Fo yFc )2]/(MyN)]1/2, where M is the number of reflec-
tions and N is the number of parameters refined.
2
2
´
3. Results and discussion
l
3.1. Synthesis and characterization
3.1.1. [Os(PPh3)2(pap)Br2]
Smooth displacement of one PPh3 from [Os(PPh3)3Br2]
by 2-(phenylazo)pyridine in refluxing 2-methoxyethanol
affords the [Os(PPh3)2(pap)Br2] complex in decent yield.
The composition of the complex was confirmed by its ele-
mental (C, H, N) analytical data (Table 2). The complex is
diamagnetic, which corresponds to the q2 oxidation state of
osmium (low-spin d6, Ss0) in this complex. As 2-(phenyl-
azo)pyridine is an unsymmetrical bidentate ligand, this
[Os(PPh3)2(pap)Br2] complex may, in principle, exist in
four geometrical isomeric forms (2–5). To find out
the actual stereochemistry of [Os(PPh3)2(pap)Br2], its
structure was determined by X-ray crystallography. The
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A. Das et al. / Polyhedron 19 (2000) 1227–1232
Table 3
structure is shown in Fig. 1 and selected bond parameters are
listed in Table 3. The pap ligand is coordinated to osmium in
the usual manner with a bite angle of 76.6(2)8. The two PPh3
ligands are mutually trans, while the two bromides occupy
mutually cis positions. The structure determination thus
showsthat[Os(PPh3)2(pap)Br2]hasstereochemistry2.The
N2P2Br2 coordination sphere around osmium is distorted
from ideal octahedral geometry, as reflected in the bond par-
ameters centering osmium. The Os–P and Os–Br bond dis-
tances are quite normal, as observed in other complexes
containing these bonds [23,24]. While the Os–N1 length is
also normal [24], the Os–N3 bond is noticeably short and
the azo N2–N3 distance is longer than the uncoordinated azo
distance [34,35]. The short Os–N3 distance and increase in
N2–N3 bond order reflect the considerable p-interaction
between osmium(II) and the azo function.
Selected bond distances and bond angles for Os(PPh3)2(pap)Br2 and
[Os(PPh3)2(pap)(acac)]ClO4
[Os(PPh3)2(pap)Br2]
[Os(PPh3)2(pap)(acac)]ClO4
Os–P1
Os–P2
Os–N1
Os–N3
Os–Br1
Os–Br2
N2–N3
2.417(2)
Os–P1
Os–P2
Os–O1
Os–O2
Os–N1
Os–N3
O1–C13
O2–C15
N2–N3
2.4485(10)
2.4740(9)
2.082(2)
2.096(2)
2.033(3)
1.977(3)
1.297(5)
1.280(4)
1.329(4)
2.430(2)
2.031(5)
1.978(5)
2.5872(7)
2.5602(7)
1.314(7)
N1–Os–N3
N1–Os–Br1
N3–Os–Br2
P1–Os–P2
76.6(2)
170.5(2)
175.05(14)
175.10(6)
N3–Os–N1
N3–Os–O1
N1–Os–O2
P1–Os–P2
O1–Os–O2
76.29(12)
171.77(11)
175.89(10)
172.77(3)
87.89(10)
1
The H NMR spectrum of [Os(PPh3)2(pap)Br2] was
recorded in CDCl3 solution. The spectrum is rather complex
in nature owing to overlapping of signals and hence assign-
ment of all the signals in this region to specific protons has
not been possible. However, two doublets (1H each)
observed at 8.22 and 7.87 ppm are assigned to the two pyri-
dine-protons of pap at positions 6 and 3, respectively (see
1). The other resonances appear within 6.7 to 7.5 ppm and
intensity measurement of these signals corresponds to the
remaining number (37) of protons present in the complex.
The IR spectrum of [Os(PPh3)2(pap)Br2] shows many
vibrations in the 1600–400 cmy1 region. Strong vibrations
observed at 740, 690, and 522 cmy1 indicate the presence of
the Os(PPh3)2 moiety [36]. A sharp and strong vibration at
1310 cmy1 is assigned to the nN_N stretch [37]. The
[Os(PPh3)2(pap)Br2] complex is poorly soluble in solvents
such as acetonitrile, acetone, ethanol, etc. and moderately
soluble in solvents such as dichloromethane, chloroform,
N,N-dimethylformamide, etc., producing intense red solu-
tion. The electronic spectrum of the complex has been
recorded in dichloromethane solution. The complex shows
intense absorptions in the visible and UV region (Table 2).
The absoptions in the UV region are attributabletotransitions
within the ligand orbitals, whereas the absorptions in the
visible region are probably due to allowed metal-to-ligand
charge-transfer transitions.
3.1.2. [Os(PPh3)2(pap)(L)]ClO4
One major objective of undertaking this present work has
been to scrutinize the reactivity of the OsBr2 fragment of
[Os(PPh3)2(pap)Br2] towards displacement by ligands of
different types. This was carried out by reacting
[Os(PPh3)2(pap)Br2] with five selected acidic ligands, i.e.
quinoline-8-ol (Hq, 6), picolinic acid (Hpic, 7), oxalic acid
(H2ox, 8), 1-nitroso-2-naphthol (Hnn, 9) and acetylacetone
(Hacaac, 10). The reactions proceed smoothly in
ethanol/2-methoxyethanolmedium(alittledichloromethane
was necessary initially to take [Os(PPh3)2(pap)Br2] into
alcoholic medium) in the presence of a base to afford the
expected complexes of the type [Os(PPh3)2(pap)(L)]q
(Lsq, pic, Hox, nn and acac). It is interesting to note here
that during the reaction with oxalic acid, only one proton is
lost and the monoanionic oxalate ion (Hox) coordinates to
osmium. The complex cations were isolated as perchlorate
salts in the solid state. Microanalytical data of these five
complexes agree well with their compositions (Table 2).
These complexes are diamagnetic which shows that the q2
state of osmium is retained in them. Several geometric iso-
Fig. 1. Structure of [Os(PPh3)2(pap)Br2].
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mers are possible for these complexes. The structure of
[Os(PPh3)2(pap)(acac)]ClO4 was determined by X-ray
crystallography. The structure is shown in Fig. 2 and selected
bond distances and angles are presented in Table 3. The
coordination sphere around osmium is N2O2P2 which is
slightly distorted octahedral in nature, as reflected in all the
bond angles with osmium as the central atom. The acetyl-
acetonate anion is coordinated to osmium as a O,O-donor
with a bite angle of 87.898. The two PPh3 ligandsaremutually
trans as observed in the parent [Os(PPh3)2(pap)Br2] com-
plex. Distances within the Os(PPh3)2(pap) fragment are
comparable to those observed in the [Os(PPh3)2(pap)Br2]
complex [23]. The bond lengths in the Os(acac) fragment
are also normal [21,38]. The other four [Os(PPh3)2-
(pap)(L)]q complexes have the same Os(PPh3)2(pap)
fragment and hence they are assumed to have similar struc-
tures with the PPh3 ligands in mutually trans positions. Syn-
thesis of the [Os(PPh3)2(pap)(L)]q complexes from
[Os(PPh3)2(pap)Br2] is therefore stereoretentive.
1H NMR spectra of the [Os(PPh3)2(pap)(L)]ClO4 com-
plexes, recorded in CDCl3 solution, show many signals in the
aromatic region and the spectra are complex in nature. In the
[Os(PPh3)2(pap)(acac)]ClO4 complex, two sharp methyl
resonances are observed at 1.67 and 1.58 ppm due to the
coordinated acac, and the central C–H proton signal of the
same ligand appears at 5.09 ppm. Infrared spectra of the
[Os(PPh3)2(pap)(L)]ClO4 complexes are mostly similar
to the spectrum of the parent [Os(PPh3)2(pap)Br2] com-
plex. Some additional vibrations are observed in all the
[Os(PPh3)2(pap)(L)]ClO4 complexes, of which the two
intense ones observed near 1100 and 625 cmy1 indicate the
presence of perchlorate ion. The nCO(carboxylate) vibration is
observed at 1700 cmy1 in the Lspic complex and at 1650
cmy1 in the LsHox complex. In the Lsnn complex the nNO
vibration is observed at 1256 cmy1. The [Os(PPh3)2-
(pap)(L)]ClO4 complexes are soluble in acetonitrile solu-
tion, producing brown solutions. Conductivitymeasurements
in acetonitrile solution show that all these complexes behave
as 1:1 electrolytes (LMs145–160 Vy1 cm2 My1), as
expected. Electronic spectra of the [Os(PPh3)2(pap)-
(L)]ClO4 complexes, recorded in acetonitrile solution
(Table 2), show several intense absorptions in the visible
and UV region as before.
Fig. 2. Structure of [Os(PPh3)2(pap)(acac)]ClO4.
Fig. 3. Cyclic voltammograms of (a) [Os(PPh3)2(pap)Br2] in dichloro-
methane solution (0.1 M TBAP) and (b) [Os(PPh3)2(pap)(Hox)]ClO4
in acetonitrile solution (0.1 M TBAP) at a scan rate of 50 mV sy1
.
cene–ferrocenium couple under identical experiment. The
reductions are assigned to reductions of the coordinated 2-
(phenylazo)pyridine ligand. The 2-(phenylazo)pyridine
ligand is known to accept successively two electrons in its
lowest unoccupied molecular orbital which is largely azo in
nature [39]. Both of these reductions are indeed observed
in [Os(PPh3)2(pap)Br2]. Cyclic voltammetry on the
[Os(PPh3)2(pap)(L)]q complexes in acetonitrile solution
also shows a reversible osmium(II)–osmium(III) oxidation
and two reductions of the coordinated pap (Table 2, Fig. 3).
The potential of the osmium(II)–osmium(III)oxidationvar-
ies significantly (0.69–1.01 V) as L is varied. Reductions of
the coordinated pap are observed below y0.9 V.
3.2. Cyclic voltammetric properties
Electrochemical properties of all the complexes were stud-
ied by cyclic voltammetry. Voltammetric data are given in
Table 2 and selected voltammograms are shown in Fig. 3.
Cyclic voltammetry on [Os(PPh3)2(pap)Br2] in dichloro-
methane solution shows a reversible oxidative response at
0.49 V (all potentials are referenced to SCE) and two quasi-
reversible reductive responses at y1.03 and y1.40 V. The
oxidation isassigned toosmium(II)–osmium(III)oxidation.
The one-electron nature of this oxidation was established by
comparing its current heights with those of standard ferro-
4. Conclusion
The Os–Br bonds in the [Os(PPh3)2(pap)Br2] complex
are found to be displaceable by bidentate chelating ligands
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[11] L.D. Cola, F. Barigelletti, V. Balzani, P. Belser, A.V. Zelewsky, C.
Seel, M. Frank, F. Vogtle, Coord. Chem. Rev. 111 (1991) 255.
[12] E.C. Constable, C.E. Housecroft, Coord. Chem. Rev. 124 (1993) 183.
[13] M.D. Ward, Coord. Chem. Rev. 127 (1993) 1.
[14] M. Furue, K. Maruyama, Y. Kanematsu, T. Kushida, M. Kamachi,
Coord. Chem. Rev. 132 (1994) 201.
under relatively mild conditions. Hence this complexappears
to be suitable as a building unit for the preparation of com-
plexes of higher nuclearity and suchpossibilitiesarecurrently
being explored.
[15] F. Barigelletti, L. Flamigni, V. Balzani, J.P. Collin, J.P. Sauvage, A.
Sour, E.C. Constable, A.M.W.C. Thompson, Coord. Chem. Rev. 132
(1994) 209.
Supplementary data
[16] K. Kalyansundaram, S.M. Zakeeruddin, M.K. Nazeeruddin, Coord.
Chem. Rev. 132 (1994) 259.
Supplementary data are available from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: q44-1223-336033; e-mail: deposit@
cdc.cam.ac.uk), on request quoting the deposition numbers
CCDC 137568 and CCDC 137569.
[17] M.G. Richmond, Coord. Chem. Rev. 141 (1995) 63.
[18] M.D. Ward, Coord. Chem. Rev. 146 (1995) 99.
[19] F. Basuli, S.M. Peng, S. Bhattacharya, Inorg. Chem. 36 (1997) 5645.
[20] F. Basuli, S.M. Peng, S. Bhattacharya, Polyhedron 17 (1998) 2191.
[21] F. Basuli, S.M. Peng, S. Bhattacharya, Polyhedron 18 (1998) 391.
[22] F. Basuli, M. Ruf, C.G. Pierpont, S. Bhattacharya, Inorg. Chem. 37
(1998) 6113.
Acknowledgements
[23] A. Das, F. Basuli, S.M. Peng, S. Bhattacharya, Polyhedron 18 (1999)
2729.
[24] B.K. Ghosh, A. Mukhopadhyay, S. Goswami, S. Ray, A. Chakravorty,
Inorg. Chem. 23 (1984) 4633.
[25] E.M. Kober, J.V. Casper, B.P. Sullivan, T.J. Meyer, Inorg. Chem. 27
(1988) 4587.
Financial assistance received from the Department of Sci-
ence and Technology, New Delhi (Grant No. SP/S1/F33/
98) is gratefully acknowledged. Thanks are also due to the
Third World Academy of Sciences for financial support ena-
bling the purchase of an electrochemical cell system.
[26] R.A. Krause, K. Krause, Inorg. Chem. 19 (1980) 2600.
[27]
S. Goswami, A.R. Chakravarty, A. Chakravorty, Inorg. Chem. 20
(1981) 2246.
[28]
[29]
[30]
[31]
[32]
R.A. Krause, K. Krause, Inorg. Chem. 21 (1982) 1714.
F.P. Dwyer, J.W. Hogarth, Inorg. Synth. 5 (1957) 204.
P.R. Hoffman, K.G. Caulton, J. Am. Chem. Soc. 97 (1975) 4221.
N. Campbell, A.W. Henderson, D. Taylor, J. Chem. Soc. (1953)1281.
D.T. Sawyer, J.L. Roberts Jr., Experimental Electrochemistry for
Chemists, Wiley, New York, 1974, pp. 167–215.
M. Walter, L. Ramaley, Anal. Chem. 45 (1973) 165.
A. Seal, S. Ray, Acta Crystallogr., Sect. C 40 (1984) 929.
P. Majumdar, S.M. Peng, S. Goswami, J. Chem. Soc., Dalton Trans.
(1998) 1569.
S. Bhattacharya, C.G. Pierpont, Inorg. Chem. 30 (1991) 2906.
B.K. Ghosh, S. Goswami, A. Chakravorty, Inorg. Chem. 22 (1983)
3358.
K. Sui, S.M. Peng, S. Bhattacharya, Polyhedron 18 (1999) 631.
S. Goswami, R.N. Mukherjee, A. Chakravorty, Inorg. Chem. 22
(1983) 2825.
References
[1] K.R. Seddon, Coord. Chem. Rev. 41 (1982) 159.
[2] D.S. Moore, Coord. Chem. Rev. 44 (1982) 127.
[3] D.J. Gulliver, W. Levason, Coord. Chem. Rev. 46 (1982) 1.
[4] E.A. Seddon, Coord. Chem. Rev. 67 (1985) 243.
[5] M.O. Albers, D.J. Robinson, E. Singleton, Coord. Chem. Rev. 79
(1987) 1.
[6] N.C. Thomas, Coord. Chem. Rev. 93 (1989) 225.
[7] D. Rong, H.G. Hong, Y.I. Kim, J.S. Krueger, J.E. Mayer, T.E.
Mallouk, Coord. Chem. Rev. 97 (1990) 237.
[8] V.W.W. Yam, C.M. Che, Coord. Chem. Rev. 97 (1990) 93.
[9] R. Hage, Coord. Chem. Rev. 111 (1991) 161.
[10] J.P. Collin, S. Guillerez, J.P. Sauvage, F. Barigelletti, L. Flamigni,
L.D. Cola, V. Balzani, Coord. Chem. Rev. 111 (1991) 291.
[33]
[34]
[35]
[36]
[37]
[38]
[39]
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