Diimine-acetylide compounds of ruthenium: The structural and spectroscopic effects of oxidation

Article abstract of DOI:10.1021/ic035181v

The reaction of Ru(Me₂bipy)(PPh₃)₂CI ₂ 1 with terminal alkynes HCCR in the presence of TIPF₆ leads to the formation of the vinylidene compounds [Ru(Me ₂bipy)(PPh₃)₂CI(

Full text of DOI:10.1021/ic035181v

Inorg. Chem. 2004, 43, 3492−3499
Diimine−Acetylide Compounds of Ruthenium: The Structural and
Spectroscopic Effects of Oxidation
,†
Christopher J. Adams* and Simon J. A. Pope‡
School of Chemistry, UniVersity of Bristol, Bristol BS8 1TS, U.K., and Department of Chemistry,
The UniVersity of Manchester, Manchester M13 9PL, U.K.
Received October 13, 2003
The reaction of Ru(Me2bipy)(PPh3)2Cl2 1 with terminal alkynes HCCR in the presence of TlPF leads to the formation
6
t
of the vinylidene compounds [Ru(Me2bipy)(PPh3)2Cl(dCdCHR)][PF ] (2) (2a, R ) Bu; 2b, R ) p-C H −Me; 2c,
6
6 4
R ) Ph). These compounds decompose in oxygenated solution to form the carbonyl compound [Ru(Me2bipy)-
(PPh3)2Cl(CO)][PF ] (3), and may be deprotonated by K CO to give the ruthenium(II) terminal acetylide compounds
6
2
3
t
Ru(Me2bipy)(PPh3)2Cl(CtC−R) (4) (4a, R ) Bu; 4b, R ) p-C H −Me; 4c, R ) Ph). Cyclic voltammetry shows
6
4
that 2a−c may also be reductively dehydrogenated to form 4a−c. 4a−c are readily oxidized to their ruthenium(III)
analogues [4a]+−[4c]+, and the changes seen in their UV/visible spectra upon performing this oxidation are analyzed.
These show that whereas the UV/visible spectra of 4a−c show MLCT bands from the ruthenium atom to the
bipyridyl ligand, those of [4a]+−[4c]+ contain LMCT bands originating on the acetylide ligands. This is in agreement
with the IR and ESR spectra of [4a]+−[4c]+. The X-ray crystal structures of the redox pair 4a and [4a][PF ] have
6
been determined, allowing the bonding within the metal−acetylide unit to be analyzed, and an attempt is made to
determine Lever electrochemical parameters (E ) for the vinylidene and acetylide ligands seen herein. Room
L
temperature luminescence measurements on 4a−c show that the compounds are not strongly emissive.
Introduction
shown to possess a metal-based HOMO and a LUMO based
upon a π* orbital on the bipyridyl, and have metal-to-ligand
charge-transfer bands in the visible region of the electromag-
netic spectrum. Furthermore, the compounds photoluminesce
There have been several recent reports on the synthesis
and chemistry of compounds of the general formula bipyridyl-
platinum-bis(acetylide).1-11 These compounds have been
3
from a MLCT state in both fluid and frozen solution.
* Author to whom correspondence should be addressed. E-mail:
chcja@bris.ac.uk.
The same trans arrangement of bipyridyl and acetylide
ligands may be envisaged about the equatorial plane of an
octahedral ruthenium complex. Ruthenium-bipyridyl sys-
tems are well-known luminophores, so this property of the
platinum systems may be preserved upon changing the
metal, but potentially there are several additional properties
that might ensue. For example, the susceptibility of ruthen-
ium(II) compounds to oxidation may allow some kind of
electrochemical switching of optical properties, and the need
to occupy the axial positions at the metal with ancillary
ligands offers both a route into enhanced solubility and, by
varying these ligands, the opportunity to “tune” the electronic
properties of the compounds. No ruthenium compounds
containing both a bipyridine and two acetylide ligands have
been reported before; in reporting details of the chemistry
of bipyridyl-ruthenium-mono(acetylide) systems, with the
axial positions of the central ruthenium atom occupied by
two triphenylphosphine ligands, this work contains details
† University of Bristol.
‡ The University of Manchester.
(1) Adams, C. J.; James, S. L.; Liu, X.; Raithby, P. R.; Yellowlees, L. J.
J. Chem. Soc., Dalton Trans. 2000, 63-67.
(2) Hissler, M.; Connick, W. B.; Geiger, D. K.; McGarrah, J. E.; Lipa,
D.; Lachicotte, R. J.; Eisenberg, R. Inorg. Chem. 2000, 39, 447-457.
(3) Whittle, C. E.; Weinstein, J. A.; George, M. W.; Schanze, K. S. Inorg.
Chem. 2001, 40, 4053-4062.
(4) McGarrah, J. E.; Kim, Y.-J.; Hissler, M.; Eisenberg, R. Inorg. Chem.
2001, 40, 4510-4511.
(5) Chan, S.-C.; Chan, M. C. W.; Wang, Y.; Che, C.-M.; Cheung, K.-K.;
Zhu, N. Chem. Eur. J. 2001, 4180-4190.
(6) Wadas, T. J.; Lachicotte, R. J.; Eisenberg, R. Inorg. Chem. 2003, 42,
3772-3778.
(7) McGarrah, J. E.; Eisenberg, R. Inorg. Chem. 2003, 42, 4355-4365.
(8) James, S. L.; Younus, M.; Raithby, P. R.; Lewis, J. J. Organomet.
Chem. 1997, 543, 233-235.
(9) Pomestchenko, I. E.; Luman, C. R.; Hissler, M.; Ziessel, R.; Castellano,
F. N. Inorg. Chem. 2003, 42, 1394-1396.
(10) Kang, Y.; Lee, J.; Song, D.; Wang, S. J. Chem. Soc., Dalton Trans.
2003, 3493-3499.
(11) Lu, W.; Chan, M. C. W.; Zhu, N.; Che, C.-M.; He, Z.; Wong, K.-Y.
Chem. Eur. J. 2003, 6155-6166.
3492 Inorganic Chemistry, Vol. 43, No. 11, 2004
10.1021/ic035181v CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/24/2004

Diimine-Acetylide Compounds of Ruthenium
was then filtered through a filter-paper-tipped cannula to remove
the white precipitate of TlCl, and 25 cm3 of diethyl ether was added.
Upon refrigeration, orange crystals of [Ru(Me2bipy)(PPh3)2Cl(d
CdCHtBu)][PF6]‚1/2C4H10O were formed, which were isolated by
filtration, washed with diethyl ether, and dried under vacuum to
give 0.213 g (0.191 mmol, 88%) of product. 1H NMR (CD2Cl2) δ:
of studies toward the synthesis of such compounds. The only
reported compound containing both an acetylide ligand and
bipyridine coordinated to a ruthenium atom is [Ru(bipy)-
(PPh3)2(CO)(-CtC-(CH2)2CH2Cl)][PF6].12
The aforementioned platinum systems are synthesized by
a copper(I) iodide catalyzed Sonogashira coupling of the
bipyridyl-metal-dichloride with a terminal alkyne in the
presence of a base. This procedure works for a wide variety
of platinum systems, but is less commonly used for ruthe-
nium systems because of the instability of many ruthenium
compounds to the strong base required. A common alterna-
tive involves the reaction of a coordinatively unsaturated 16-
electron ruthenium fragment with a terminal alkyne to
generate a vinylidene compound (via η2 coordination of the
alkyne followed by a 1,2-hydrogen migration), followed by
deprotonation with a mild base to give the desired acetylide
product.13 This is the method employed herein.
0.95 (9H, s, tBu); 2.35, 2.38 (each 3H, s, Me); 3.28 (1H, t, 4JHP
)
3.3 Hz, Hvinylidene); 6.24 (1H, d, 3JHH ) 6.1 Hz, Hbipy); 6.58 (1H, d,
3JHH ) 5.8 Hz, Hbipy); 7.03-7.27 (31H, m, Hbipy and HPh); 7.85,
3
7.90 (each 1H, s, Hbipy); 8.34 (1H, d, JHH ) 5.8 Hz, Hbipy). 31P
NMR (CD2Cl2) δ: 20.8 (s). FAB+: m/z 927 [M]+. Anal. Calcd
for C56H57N2RuP3F6ClO0.5: C, 60.62; H, 5.18; N, 2.52. Found: C,
60.67; H, 4.87; N, 2.73.
[Ru(Me2bipy)(PPh3)2Cl(dCdCH-p-C6H4-Me)][PF6] (2b). 1
(0.287 g, 0.33 mmol), 0.114 g (0.33 mmol) of TlPF6, and 0.1 cm3
(0.79 mmol) of 4-ethynyltoluene were stirred for 2 h in 30 cm3 of
CH2Cl2. The resulting orange-brown suspension was filtered through
a filter-paper-tipped cannula to remove precipitated TlCl, and 50
cm3 of diethyl ether was added to the stirred filtrate. On refrigera-
tion, yellow-brown crystals of the desired product were formed,
which were isolated by filtration, washed with diethyl ether, and
dried under vacuum. Yield: 0.218 g (0.20 mmol, 61%). 1H NMR
Experimental Section
All new compounds are air stable in the solid state and reasonably
air stable in solution, but standard inert-atmosphere techniques were
used throughout. All solvents were purified using an Anhydrous
Engineering Grubbs-type solvent system.14 The starting material
Ru(Me2bipy)(PPh3)2Cl2 (1) was prepared by literature methods,15
and all other chemicals were used as purchased. IR and UV/visible
spectra were recorded in dichloromethane solution on a Perkin-
Elmer 1600 series FTIR spectrometer and a Perkin-Elmer λ-19
spectrophotometer, respectively. Cyclic voltammetry was carried
out under an atmosphere of nitrogen using the standard three
electrode configuration, with platinum working and counter elec-
trodes, an SCE reference electrode, dichloromethane as solvent,
0.1 M [Bu4N][PF6] as electrolyte and FeCp2 or FeCp*2 as internal
calibrant, and a substrate concentration of approximately 1 mM.
All potentials are reported vs the SCE reference electrode, against
which the FeCp2/[FeCp2]+ couple comes at 0.46 V and FeCp*2/
[FeCp*2]+ is -0.02 V.16 The anisotropic ESR spectra of [4a]+-
[4c]+ were recorded on a Bruker ESP300E X-band spectrometer
calibrated with dpph in frozen 2:1 thf CH2Cl2 solution. NMR spectra
were recorded in CD2Cl2 on a JEOL ECP300 spectrometer, at 300
MHz (1H) and 121 MHz (31P), and referenced to external TMS
and external 85% H3PO4, respectively. UV/visible spectroelectro-
chemical measurements were performed in CH2Cl2 at 243 K using
a locally constructed OTTLE (optically transparent thin-layer
electrode) cell in a Perkin-Elmer λ-19 spectrophotometer, as
described previously.17 Luminescence measurements were con-
ducted using a Perkin-Elmer LS55 fluorimeter. Microanalyses were
carried out by the staff of the Microanalytical Service of the School
of Chemistry at the University of Bristol.
(CD2Cl2) δ: 2.29, 2.37, 2.38 (each 3H, s, Me); 4.70 (1H, t, 4JHP
)
3
3.5 Hz, Hvinylidene); 6.16 (1H, d, JHH ) 5 Hz, Hbipy); 6.64 (1H, d,
3JHH ) 5.8 Hz, Hbipy); 6.83 (2H, d, 3JHH ) 8 Hz, Tol); 6.92 (1H, d,
3JHH ) 5 Hz, Htolyl); 6.97-7.24 (32H, m, Hbipy and HPh); 7.93 (2H,
s, Hbipy); 8.34 (1H, d, 3JHH ) 5.8 Hz, Hbipy). 31P NMR (CD2Cl2) δ:
21.0 (s). FAB+: m/z 962 [M + H]+. Anal. Calcd for C57H50N2-
RuP3F6Cl: C, 61.87; H, 4.55; N, 2.53. Found: C, 61.35; H, 4.58;
N, 2.56.
[Ru(Me2bipy)(PPh3)2Cl(dCdCHC6H5)][PF6] (2c). 1 (0.325 g,
0.37 mmol), 0.129 g of TlPF6 (0.37 mmol), and 0.1 cm3 of
phenylacetylene (1.05 mmol) were stirred for 2 h in 30 cm3 of
CH2Cl2 to give a cloudy solution. This was filtered, and 60 cm3 of
diethyl ether was added. Upon refrigeration, the solution deposited
orange-brown crystals of 2c, which were isolated by filtration,
washed with diethyl ether, and dried in vacuo. Yield: 0.288 g (0.26
1
mmol, 70%). H NMR (CD2Cl2) δ: 2.37, 2.39 (each 3H, s, Me);
4.75 (1H, t, 4JHP ) 3.5 Hz, Hvinylidene); 6.19 (1H, d, 3JHH ) 5.8 Hz,
3
H
bipy); 6.64 (1H, d, JHH ) 5.8 Hz, Hbipy); 6.92-7.25 (36H, m,
3
Hbipy and HPh); 7.95 (2H, s, Hbipy); 8.33 (1H, d, JHH ) 5.8 Hz,
H
bipy). 31P NMR (CD2Cl2) δ: 20.7 (s). FAB+: m/z 947 [M]+. Anal.
Calcd for C56H48N2RuP3F6Cl: C, 61.57; H, 4.43; N, 2.56. Found:
C, 61.76; H, 4.63; N, 2.38.
[Ru(Me2bipy)(PPh3)2Cl(CO)][PF6] (3). 1 (0.151 g, 0.17 mmol)
and 0.060 g of TlPF6 (0.17 mmol) were stirred in 10 cm3 of CH2-
Cl2 for 1 h under a carbon monoxide atmosphere. The resulting
bright yellow suspension was then filtered through a filter-paper-
tipped cannula to remove the white precipitate of TlCl, and 15 cm3
of diethyl ether was added. Upon standing, pale yellow crystals of
3 were formed, which were isolated by filtration, washed with
diethyl ether, and dried under vacuum to give 0.136 g (0.13 mmol,
77%) of product, which may be recrystallized as yellow-green plates
by allowing vapor diffusion of diethyl ether into a dichloromethane
Syntheses. [Ru(Me2bipy)(PPh3)2Cl(dCdCHBut)][PF6]‚0.5Et2O
(2a‚0.5Et2O). 1 (0.191 g, 0.216 mmol), 0.075 g of TlPF6 (0.216
mmol), and 0.2 cm3 (1.62 mmol) of tert-butylacetylene were stirred
in 10 cm3 of CH2Cl2 for 2 h. The resulting yellow-brown solution
1
solution. H NMR (CD2Cl2) δ: 2.35, 2.47 (each 3H, s, Me); 6.22
3
3
(1H, d, JHH ) 5.8 Hz, Hbipy); 6.68 (1H, d, JHH ) 5.8 Hz, Hbipy);
7.15-7.35 (31H, m, Hbipy and HPh); 7.90, 8.04 (each 1H, s, Hbipy);
8.28 (1H, d, 3JHH ) 5.8 Hz, Hbipy). 31P NMR (CD2Cl2) δ: 27.1 (s).
FAB+: m/z 873 [M]+. FT-IR (CH2Cl2) ν(CtO) (cm-1): 1964.
Anal. Calcd for C49H42N2RuOP3F6Cl: C, 57.80; H, 4.16; N, 2.75.
Found: C, 57.74; H, 4.00; N, 2.74.
(12) Santos, A.; Lopez, J.; Galan, A.; Gonzalez, J. J.; Tinoco, P.;
Echavarren, A. M. Organometallics 1997, 16, 3482-3488.
(13) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586-
2617.
(14) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.
(15) Adams, C. J. J. Chem. Soc., Dalton Trans. 2002, 1545-1550.
(16) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-910.
(17) Lee, S.-M.; Kowallick, R.; Marcaccio, M.; McCleverty, J. A.; Ward,
M. D. J. Chem. Soc., Dalton Trans. 1998, 3443-3450.
[Ru(Me2bipy)(PPh3)2Cl(-CtC-But)] (4a). 2a‚0.5Et2O (0.096
g, 0.086 mmol) and 0.050 g of potassium carbonate (0.36 mmol)
Inorganic Chemistry, Vol. 43, No. 11, 2004 3493

Adams and Pope
were stirred overnight in 10 cm3 of thf; 10 cm3 of hexane was added
to the resulting solution, which was then filtered and evaporated
to dryness. The brown solid thus obtained was redissolved in 10
cm3 of toluene, and then 10 cm3 of hexane was added to the
resulting solution, which was filtered. Storage at 4 °C for 72 h
gave the desired product as a brown microcrystalline solid, which
was isolated by filtration, washed with hexane, and dried under
vacuum to yield 0.040 g (0.043 mmol, 50%) of 4a. Large cubic
crystals of 4a‚C4H10O for X-ray structure determination were
isolated from a dichloromethane/diethyl ether solution of the
Scheme 1. Synthesis of Compounds 2a-c
1
compound stored at -10 °C. H NMR (CD2Cl2 + [NEt4]Cl) δ:
1.03 (9H, s, tBu), 2.10, 2.20 (each 3H, s, Me), 5.85 (1H, d, 3JHH
)
6.0 Hz, Hbipy), 6.46 (1H, d, 3JHH ) 5.8 Hz, Hbipy), 6.93-7.08 (18H,
m, HPh), 7.30, 7.39 (each 1H, s, Hbipy), 7.52-7.60 (12H, m, HPh),
(2 × 5 cm3) and dried under vacuum to give about 0.020 g (0.016
mmol, 53%) of the desired product, suitable for X-ray diffraction
study. Anal. Calcd for C64H71N2RuO2.5P3ClF6: C, 61.41; H, 5.72;
N, 2.24. Found: C, 61.96; H, 5.46; N, 2.77.
Crystal Structure Determinations. Data collection was carried
out on a Bruker SMART diffractometer, with the crystal mounted
in a nitrogen stream at -100 °C. Data correction was performed
using the program SADABS,18 and the structure was solved by
direct methods and refined by full-matrix least-squares techniques
against F2 using the programs SHELXS-9719 and SHELXL-97.20
The thf molecules in the structure of [4a][PF6]‚2.5thf are all
disordered to some extent, and were refined isotropically without
the addition of hydrogen atoms.
3
3
8.34 (1H, d, JHH ) 6.0 Hz, Hbipy), 8.61 (1H, d, JHH ) 6.0 Hz,
H
bipy). 31P NMR (CD2Cl2 + [NEt4]Cl) δ: 30.9 (s). FAB+: m/z 926
[M]+. FT-IR (CH2Cl2) ν(CtC) (cm-1): 2078. Anal. Calcd for
C54H51N2RuP2Cl: C, 70.01; H, 5.55; N, 3.02. Found: C, 70.41;
H, 5.84; N, 2.89.
[Ru(Me2bipy)(PPh3)2Cl(-CtC-p-C6H4-CH3)] (4b). 2b (0.092
g, 0.083 mmol) and 0.092 g of potassium carbonate (0.66 mmol)
were stirred overnight in 10 cm3 of CH2Cl2; 20 cm3 of hexane was
added to the resulting brown solution, which was then filtered and
evaporated to dryness in vacuo. The brown solid thus obtained was
extracted in 10 cm3 of toluene, and this solution was filtered and
reduced in volume under vacuum until some solid material began
to appear. Storage at 4 °C overnight gave the product as brown
crystals, which were isolated by filtration, washed with hexane,
and dried under vacuum to give 0.052 g (0.054 mmol, 65%) of 4b.
1H NMR (CD2Cl2 + [NEt4]Cl) δ: 2.11, 2.18, 2.23 (each 3H, s,
Crystal Data. 4a‚C4H10O: C58H61ClN2OP2Ru, M ) 1000.55,
orthorhombic, a ) 27.180(5) Å, b ) 12.912(3) Å, c ) 14.454(3)
Å, V ) 5072.5(18) Å3, T ) 173(2) K, λ ) 0.71073 Å, space group
Pna21 (No. 33), Z ) 4, µ(Mo KR) ) 0.466 mm-1, 32468 reflections
measured, 10671 unique (Rint ) 0.0716), R1 [I > 2σ(I)] ) 0.0446,
3
3
Me), 5.87 (1H, d, JHH ) 6.2 Hz, Hbipy), 6.55 (1H, d, JHH ) 5.8
Hz, Hbipy), 6.76-6.82 (4H, m, C6H4), 6.90-7.08 (18H, m, HPh),
7.34, 7.45 (each 1H, s, Hbipy), 7.48-7.57 (12H, m, HPh), 8.15 (1H,
R1 [all data] ) 0.0866. [4a][PF6]‚2.5C4H8O: C64H51ClF6N2O2.5
-
P3Ru, M ) 1231.50, triclinic, a ) 11.826(8) Å, b ) 13.962(6) Å,
c ) 19.020(11) Å, R ) 78.56(5)°, â ) 87.14(4)°, γ ) 80.52(6) °,
V ) 3035(3) Å3, T ) 173(2) K, λ ) 0.71073 Å, space group P1h
(No. 2), Z ) 2, µ(Mo KR) ) 0.444 mm-1, 31738 reflections
measured, 13796 unique (Rint ) 0.0748), R1 [I > 2σ(I)] ) 0.0664,
R1 [all data] ) 0.1346.
d, JHH ) 6.0 Hz, Hbipy), 8.71 (1H, d, JHH ) 5.8 Hz, Hbipy). 31P
NMR (CD2Cl2 + [NEt4]Cl) δ: 31.1 (s). FAB+: m/z 960 [M]+.
FT-IR (CH2Cl2) ν(CtC) (cm-1): 2067, 2043sh. Anal. Calcd for
C57H49N2RuP2Cl: C, 71.28; H, 5.14; N, 2.92. Found: C, 71.40;
H, 5.10; N, 2.53.
3
3
[Ru(Me2bipy)(PPh3)2Cl(-CtC-C6H5)] (4c). 2c (0.098 g,
0.089 mmol) and 0.098 g of potassium carbonate (0.70 mmol) were
stirred overnight in 10 cm3 of CH2Cl2; 20 cm3 of hexane was added
to the resulting solution, which was then filtered and evaporated
to dryness in vacuo. The brown solid thus obtained was extracted
in 10 cm3 of toluene, and this solution was filtered and reduced in
volume under vacuum until about to crystallize. Storage at 4 °C
for 3 days gave the product as brown crystals, which were isolated
by filtration, washed with hexane, and dried under vacuum to give
0.043 g (0.045 mmol, 51%) of 4c. 1H NMR (CD2Cl2 + [NEt4]Cl)
δ: 2.11, 2.22 (each 3H, s, Me), 5.88 (1H, d, 3JHH ) 6.0 Hz, Hbipy),
6.55 (1H, d, 3JHH ) 5.8 Hz, Hbipy), 6.82-7.08 (23H, m, HPh), 7.31,
7.43 (each 1H, s, Hbipy), 7.48-7.56 (12H, m, HPh), 8.15 (1H, d,
3JHH ) 6.0 Hz, Hbipy), 8.72 (1H, d, 3JHH ) 5.8 Hz, Hbipy). 31P NMR
(CD2Cl2 + [NEt4]Cl) δ: 31.2 (s). FAB+: m/z 684 [M - PPh3]+.
FT-IR (CH2Cl2) ν(CtC) (cm-1): 2063. Anal. Calcd for C56H47N2-
RuP2Cl: C, 71.07; H, 5.01; N, 2.96. Found: C, 71.42; H, 4.94; N,
3.40.
Results
Vinylidene and Carbonyl Complexes. The trans di-
imine-dichloride ruthenium starting material Ru(Me2bipy)-
(PPh3)2Cl2 1 (Me2bipy ) 4,4′-dimethyl-2,2′-bipyridyl) reacts
with terminal alkynes in the presence of 1 equiv of the
chloride abstractor TlPF6 to give the ionic vinylidene
compounds [Ru(Me2bipy)(PPh3)2Cl(dCdCHR)][PF6] (2a, R
) But; 2b, R ) p-C6H4-Me; 2c, R ) C6H5) in good yield
as air stable yellow-brown solids (Scheme 1). Analytical and
spectroscopic data are in accordance with their formulation
and are comparable with those reported in the literature for
other ruthenium-vinylidene compounds; thus their 1H NMR
spectra contain a characteristic signal at between 3 and 5
ppm for the vinylidene proton. The trans nature of the
triphenylphosphine ligands is confirmed by the splitting of
this vinylidene signal into a triplet due to coupling to two
equivalent phosphorus nuclei (4J ≈ 3.5 Hz), and by the single
[Ru(Me2bipy)(PPh3)2Cl(-CtC-But)][PF6]‚2.5thf ([4a][PF6]‚
2.5thf). 4a (0.028 g, 0.03 mmol) and 0.010 g (0.03 mmol) of
ferrocenium hexafluorophosphate were dissolved in 5 cm3 of thf
to give a purple solution. To this was added 5 cm3 of hexane, and
the solution was filtered. Refrigeration for 6 h caused the formation
of purple crystals of [4a][PF6]‚2.5thf. The supernatant liquid was
removed with a syringe, and the crystals were washed with hexane
(18) Sheldrick, G. M. SADABS, version 2.03; University of Go¨ttingen:
Go¨ttingen, 2001.
(19) Sheldrick, G. M. SHELXS-97, Program for crystal structure solution;
University of Go¨ttingen: Go¨ttingen, 1997.
(20) Sheldrick, G. M. SHELXL-97, Program for crystal structure refine-
ment; University of Go¨ttingen: Go¨ttingen, 1997.
3494 Inorganic Chemistry, Vol. 43, No. 11, 2004

Diimine-Acetylide Compounds of Ruthenium
Table 1. Electrochemical Data for All Compounds
Ep/V
E1/2/V
EL/V
2a
2b
2c
3
4a
4b
4c
-1.47
-1.35
-1.39
-1.44
a
1.11
1.19
1.69
0.04
0.13
0.16
0.47
0.55
1.05
-0.60
-0.51
-0.48
a No reversible oxidation process; an irreversible process with a peak
potential of 1.57 V is seen.
Figure 2. UV/visible spectra of 1 and 4a-c. In ascending order of ꢀ at
350 nm: 1, 4a, 4b, 4c.
Table 2. UV/Visible Data for 1 and 4a-c
λ
max/nm (ꢀ/103 M-1 cm-1
)
1
272 (37.9)
277 (29.6)
283 (28.4)
281 (31.6)
299 (20.1)
298 (20.3)
299 (25.8)
297 (28.0)
346 (6.1)
492 (3.2)
501 (3.4)
493 (2.7)
490 (3.7)
4a
4b
4c
353 (6.7)
331 (12.1)
336 (15.3)
Figure 1. CV of 2a, scanned from -0.2 V to 0.25 V to -1.7 V to 0.25
V to -0.2 V, showing how the product wave at 0.04 V is generated by the
irreversible process at -1.47 V.
oxidation at 1.69 V in the cyclic voltammogram, and also
has an irreversible reduction at -1.44 V.
Scheme 2. Synthesis of Compounds 4
Acetylide Complexes. The vinylidene compounds 2a-c
can readily be deprotonated to form the terminal acetylide
complexes Ru(Me2bipy)(PPh3)2Cl(CtCR) (4a, R ) But; 4b,
R ) p-C6H4-Me; 4c, R ) C6H5) (Scheme 2). A number of
different bases will effect this reaction, but for ease of
separation a suspension of K2CO3 was found to be best. The
solution IR spectra of the acetylide compounds each show
the expected CtC absorption between 2040 and 2080 cm-1,
and in addition compound 4b displays a second CtC feature
as a shoulder at 2043 cm-1 on the strong absorption at 2067
cm-1. The most probable explanation for this is Fermi
coupling, which has been observed to create two CtC peaks
in the spectra of mono-acetylide compounds before.21,22 This
occurs when an overtone or combination band that is normal-
ly of negligible intensity is able to gain intensity through an
interaction with a CtC mode of similar energy and the same
symmetry.23 The 31P NMR spectra of 4a-c are broadened
at room temperature, probably due to the transient loss of a
chloride ion from the compounds since the spectra become
sharp on the addition of [NEt4]Cl to the solution.
PPh3 signal seen in the 31P NMR. Compounds 2a-c may
also be synthesized from 1 and the appropriate alkyne with
[NH4][PF6] as the halide acceptor and anion source, but the
reaction is much slower than with TlPF6.
Cyclic voltammetry of 2a-c shows that the compounds
all display an irreversible cathodic process, at around -1.35
V (Table 1). Following this process a product wave is
observed between 0 and 0.4 V, in a position corresponding
to that seen in the CV of the corresponding compound 4
(vide infra) (Figure 1). Thus, reduction of the vinylidene
compound generates the associated acetylide compound,
presumably by the elimination of hydrogen:
The UV/visible spectral data for 4a-c are summarized in
Table 2 and presented in Figure 2. Like the parent dichloride
complex 1, compounds 4a-c have four major absorption
bands in the 250-500 nm range, and in the case of 1 all but
the highest energy of these have previously been attributed
to ruthenium-to-bipyridyl MLCT transitions.24 However,
were this the case, then it would be expected that on
oxidation of the metal center they would be shifted signifi-
cantly to higher energy, or disappear altogether. This is true
[RudCdCHR]+ + e- f Ru-CtC-R + 1/2H2
In addition, compounds 2b and 2c both display a RuII/III
oxidation couple, at 1.11 and 1.19 V, respectively, which is
almost fully reversible for 2b and which is reversible at scan
speeds above 250 mV s-1 for 2c. 2a displays only an
irreversible anodic processes.
Solutions of 2a-c decompose slowly in air to give the
carbonyl compound [Ru(Me2bipy)(PPh3)2Cl(CO)][PF6] (3),
due to reaction between the vinylidene group and atmo-
spheric oxygen. 3 may be deliberately synthesized by reaction
of 1 with 1 equiv of TlPF6 under a carbon monoxide
atmosphere; it is pale yellow when pure, but is often
discolored by impurities. 3 displays a reversible RuII/RuIII
(21) Denis, R.; Toupet, L.; Paul, F.; Lapinte, C. Organometallics 2000,
19, 4240-4251.
(22) Paul, F.; Mevellec, J.-Y.; Lapinte, C. J. Chem. Soc., Dalton Trans.
2002, 1783-1790.
(23) Ebsworth, E. A. V.; Rankin, D. W. H.; Cradock, S. Structural Methods
in Inorganic Chemistry; Blackwell Scientific Publications: Oxford,
1987.
Inorganic Chemistry, Vol. 43, No. 11, 2004 3495

Adams and Pope
Table 3. Spectroscopic Data for [4a]+-[4c]+
gx gy gz
2.387 2.249 1.865 2.167 568
g
λ
max/nm
ν(CtC)/cm-1
[4a]+
2010
1948
1959
[4b]+ 2.286 2.216 1.881 2.127 739, 678
[4c]+
2.370 2.281 1.860 2.170 701, 627
for the two lowest energy bands (at around 490 and 330-
350 nm) (vide infra), but not for the band at about 300 nm,
which may therefore be assigned to a ligand localized bipy
π f π* transition. This is also the origin of the band at
around 280 nm. The cyclic voltammograms of the acetylide
compounds 4a-c all show reversible oxidation waves
corresponding to the RuII/III couple at relatively low potentials,
meaning that their ruthenium(III) analogues [4a]+-[4c]+ can
be readily made by chemical or electrochemical oxidation.
[4a][PF6] is stable enough to be isolated whereas salts of
[4b]+ and [4c]+ are not, but these ions are readily generated
in situ for spectroscopic characterization. Thus, ESR spec-
troscopy was performed on samples of 4a-c oxidized by
ferrocenium hexafluorophosphate under a nitrogen atmo-
sphere in an ESR tube, and IR spectra were obtained by oxi-
dizing solutions of 4a-c with ferrocenium hexafluorophos-
phate and transferring the resulting solutions under nitrogen
to the IR cell. Ferrocenium hexafluorophosphate is a suitable
choice because both it and ferrocene are IR and ESR silent
in the regions of interest, but this is not the case in the UV/
visible region. Therefore, UV/visible spectra were collected
spectroelectrochemically using an OTTLE cell. The integrity
of the spectroelectrochemical results was checked by revers-
ing the oxidation after the process had finished and checking
that the spectrum returned to that of the starting material,
and was also shown by the tight isosbestic points observed.
Spectroscopic results for the ions [4a]+-[4c]+ are collected
in Table 3 and show that upon oxidation the energy of the
CtC absorption in the IR spectrum decreases substantially.
The ESR results are similar to those reported for [1][BF4],
a frozen solution giving a rhombic spectrum with closely
spaced gx and gy values and a much lower gz value. It should
be noted that the cations [4a]+-[4c]+ are all air sensitive
(especially [4b]+ and [4c]+), decomposing to 3.
The most striking observation about the ruthenium(III) ions
is their vivid color. Whereas the ruthenium(II) acetylide
compounds are red-brown, the ruthenium(III) analogue [4a]+
is magenta, and the aryl compounds [4b]+-[4c]+ are blue-
green. This is recorded in their UV/visible spectra, where-
upon oxidation of the parent ruthenium(II) compound the
MLCT bands at around 490 and 330-350 nm diminishes
dramatically in intensity, and a new low-energy band appears
in the range 568-739 nm; as an example, the spectrum of
4c during electrolysis is shown in Figure 3.
Crystal Structure Determinations. The structures of the
redox pair of compounds 4a and [4a][PF6] have both been
determined by X-ray diffraction; that of 4a is shown in Figure
4 and is indistinguishable to the naked eye from that of [4a]+.
A comparison of selected bond lengths and angles is given
Figure 3. The UV/visible spectrum of 4c during oxidation, showing the
LMCT charge-transfer band that grows at around 700 nm.
Figure 4. ORTEP plot of 4a (ellipsoids at the 50% probability level).
Hydrogen atoms have been omitted for clarity.
in Table 4 (the same numbering scheme was used in both
cases), and shows that in both cases the geometry around
the ruthenium atom is approximately octahedral, with devia-
tion from this caused by the small bite angle of the bipyridyl
ligand. The two axial triphenylphosphine ligands are slightly
bent away from a linear trans geometry toward the space
between the chloride and acetylide ligands, and the large
trans influence of the acetylide ligand is shown by the
ruthenium-nitrogen distances, that opposite the chloride
{Ru(1)-N(2)} being shorter than that opposite the acetylide
{Ru(1)-N(1)}. Otherwise the structures are unremarkable,
bond lengths within the metal-acetylide fragment of the
ruthenium(II) compound 4a being similar to those reported
for a number of ruthenium(II) piano-stool type complexes
with the same terminal tert-butylacetylide ligand.25 Variation
between the two structures will be discussed below.
Discussion
Electrochemistry. The reductive dehydrogenation of
vinylidene compounds as demonstrated for compounds 2a-c
(24) Batista, A. A.; Santiago, M. O.; Donnici, C. L.; Moreira, I. S.; Healy,
P. C.; Berners-Price, S. J.; Queiroz, S. L. Polyhedron 2001, 20, 2123-
2128.
(25) Bruce, M. I.; Hall, B. C.; Zaitseva, N. N.; Skelton, B. W.; White, A.
H. J. Chem. Soc., Dalton Trans. 1998, 1793-1803.
3496 Inorganic Chemistry, Vol. 43, No. 11, 2004

Diimine-Acetylide Compounds of Ruthenium
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 4a and [4a]+ a
bond
4a
[4a]+
∆
angle
4a
[4a]+
∆
Ru(1)-N(1)
Ru(1)-N(2)
Ru(1)-Cl(1)
Ru(1)-C(13)
C(13)-C(14)
Ru(1)-P(1)
Ru(1)-P(2)
2.120(4)
2.051(3)
2.4638(12)
2.053(5)
1.174(6)
2.152(4)
2.091(4)
2.3451(18)
1.974(5)
1.197(7)
2.385(20)
2.398(20)
+0.032(6)
P(1)-Ru(1)-P(2)
N(1)-Ru(1)-C(13)
N(2)-Ru(1)-Cl(1)
Cl(1)-Ru(1)-C(13)
N(1)-Ru(1)-N(2)
Ru(1)-C(13)-C(14)
C(13)-C(14)-C(15)
172.02(4)
171.17(15)
169.16(10)
97.89(12)
78.40(14)
173.6(4)
174.67(5)
168.98(18)
168.96(12)
98.73(16)
76.96(17)
177.2(5)
+2.65(6)
-1.19(23)
-0.20(16)
+0.84(20)
-1.44(22)
+3.6(6)
+0.040(5)
-0.1187(22)
-0.079(7)
+0.023(9)
2.3470(13)
2.3697(13)
+0.0380(24)
+0.0283(24)
176.1(6)
179.7(6)
+3.6(8)
a ∆ is the change upon oxidation.
Figure 5. Qualitative MO diagram for 4a-c and [4a]+-[4c]+, viewed down the P-Ru-P (z) axis, showing the interaction of the ruthenium t2g orbitals
with the vacant π orbitals of the triphenyphosphine and the filled π orbitals of the acetylide and chloride ligands. Interaction with the π-type orbitals of the
chloride and bipyridyl ligands is not shown, but does not alter the ordering of orbitals. For the d5 Ru(III) case (shown), the LMCT transition is shown by
the dotted arrow.
is not a novel process, although it has not been seen in
ruthenium compounds before; Bianchini has demonstrated
that, in certain cobalt26 and rhodium27 systems, one-electron
reduction of the vinylidene complex liberates hydrogen and
forms the corresponding acetylide. Much more common is
the oxidative formation of acetylide from vinylidene with
accompanying loss of a proton, which has been demonstrated
in a ruthenium system;28 however, the oxidative decomposi-
tion of 2a in the cyclic voltammogram is not accompanied
by a daughter peak from the acetylide.
(dppe)2], trans-[RuCl(CtCPh)(dppe)2] and trans-[Ru-
(CtCPh)2(dppe)2] are 0.60, 0.55, and 0.56 V, respectively,
which clearly indicate a nonlinear trend upon replacing
chloride by phenylacetylide.30
A previous attempt has been made to assign EL parameters
to vinylidene ligands, though by a more indirect method.31
The values given for tolyl- and phenyl-vinylidene were
0.51 and 0.52 V, compared to values calculated by the above
method from the data for 2b and 2c of 0.47 and 0.55 V,
respectively.
In recent years many ligands have been assigned EL values,
electrochemical parameters based on the additive system
proposed by Lever,29 but there does not seem to have been
any attempt to do so for acetylide systems. Compounds 4a-c
present an opportunity to do this, especially since all the other
ligands in the complex have been parametrized by Lever.
Taking the published values of EL (0.46 V for Me2bipy, 0.39
V for PPh3 and -0.24 V for Cl-) predicts that E1/2 for 1
should be 0.76 V vs NHE in acetonitrile. The published value
of 0.40 V vs SCE in dichloromethane15 allows a correction
of -0.36 V to be made for differences in conditions. The
difference in oxidation potential between the acetylide
compounds and the dichloride compound 1 must be the same
as the difference in EL for the acetylide ligand and the
chloride ligand that it replaces; so, for example, compound
4a is oxidized at 0.04 V, 0.36 V less than 1. Therefore, EL
for the tert-butylacetylide ligand must be 0.36 V less than
the value for chloride (-0.24 V), equaling -0.60 V. Values
derived in the same way for all the acetylide ligands in this
study are shown in Table 1. The value of EL (CO) derived
in this way from the data for compound 3 is 1.05 V, which
may be compared to the published value of 0.99 V to give
an indication of the error involved. It is noteworthy that the
published oxidation potentials (vs Ag/AgCl) of trans-[RuCl2-
Molecular Orbitals. The ordering of the doubly occupied
metal d orbitals of t2g origin in 1 has been assigned as 1
over 2; that is, the dxz and dyz interact with the moderately
π-accepting triphenylphosphine ligand and are lowered in
energy, whereas the dxy orbital has only in-plane π-donor
interactions with the chloride and ligands, and is the
HOMO.32 This arrangement of orbitals is also true for
4a-c, with the added complication of dxz and dyz no longer
being degenerate because of the replacement of one chloride
ligand with an acetylide group (Figure 5). (There has been
considerable debate about the π-character of acetylide ligands
over the years, but the consensus appears to be that in the
(26) Bianchini, C.; Innocenti, P.; Meli, A.; Peruzzini, M.; Zanobini, F.;
Zanello, P. Organometallics 1990, 9, 2514-2522.
(27) Bianchini, C.; Meli, A.; Peruzzini, M.; Zanobini, F.; Zanello, P.
Organometallics 1990, 9, 241-250.
(28) Hurst, S. K.; Cifuentes, M. P.; Morrall, J. P. L.; Lucas, N. T.; Whittall,
I. R.; Humphrey, M. G.; Asselberghs, I.; Persoons, A.; Samoc, M.;
Luther-Davies, B.; Willis, A. C. Organometallics 2001, 20, 4664-
4675.
(29) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271-1285.
(30) Powell, C. E.; Cifuentes, M. P.; Morrall, J. P.; Stranger, R.; Humphrey,
M. G.; Samoc, M.; Luther-Davies, B.; Heath, G. A. J. Am. Chem.
Soc. 2003, 125, 602-610.
(31) Almeida, S. S. P. R.; Pombeiro, A. J. L. Organometallics 1997, 16,
4469-4478.
(32) Chakravarty, J.; Bhattacharya, S. Polyhedron 1994, 13, 2671-2678.
Inorganic Chemistry, Vol. 43, No. 11, 2004 3497

Adams and Pope
majority of cases they act as π-donor ligands with little metal-
to-ligand back-bonding. Replacement of chloride by acetylide
should therefore cause little change in the ordering of
orbitals.)33,34 Thus, on oxidation of 4a-4c from ruthenium-
(II) to ruthenium(III) the electron is removed from the dxy
orbital, creating a metal-based SOMO that causes <g> to
deviate from 2.00.
This MO scheme is supported by the bond lengths seen
in the crystallographically determined structures of the redox
pair 4a and [4a][PF6]. Upon oxidation, the major changes
in bond length are shortenings of the metal-chloride (by
0.119(2) Å) and metal-acetylide (by 0.079(7) Å) distances,
consistent with the removal of an electron from a metal
orbital that is antibonding with respect to both of these
ligands. This must be the dxy orbital, as it is the sole occupied
orbital lying in the plane of both these ligands. The
ruthenium-phosphorus bond lengths increase slightly (by
approximately 0.04 Å), in line with previous studies on the
nature of metal-phosphine bonding in redox pairs.35
The structures of 4a and [4a][PF6] appear to constitute
the fourth crystallographically characterized metal-acetylide
redox pair; those reported previously have been [Mn(dppe)-
(CtCPh)2]0/1,36 [Fe{P(CH2CH2PPh2)3}(CtCPh)]0/1,37 and
[Mo(dppe)(η-C7H7)(CtCPh)]0/1,38 although the large esd’s
on the first two of these pairs preclude any meaningful
discussion of bond length changes on oxidation. The last
pair is a d6/d5 pair as in the current work, and shows a similar
decrease (of 0.071(10) Å) in the metal-acetylide distance.
These decreases provide further support for the absence of
π back-bonding in metal acetylide complexes; if this interac-
tion were present it would be bonding between the dxy orbital
and the ligand π system, and the metal-acetylide bond length
would be expected to increase upon depopulating the
resultant MO.
UV/Visible Spectra of Ru(III) Compounds. The new
absorption observed in the UV/visible spectrum following
oxidation of 4a-c has no counterpart in the spectrum of
[1][BF4], the analogous ruthenium(III) dichloride compound,
and therefore would appear to have some acetylide character.
As the π orbitals of the carbon-carbon triple bond are the
frontier orbitals of this ligand and the LUMO of the
compound is now the metal-based dxy SOMO, this band can
be assigned to a π f dxy LMCT transition. In the tert-
butylacetylide fragment of 4a both alkyne triple-bond π
orbitals are degenerate (assuming free rotation of the tert-
butyl group), but in the arylacetylides 4b and 4c they are
not;33 which of the π orbitals is the donor depends upon the
(unknown) orientation of the aryl ring.
Figure 6. The LMCT bands seen in the UV/visible spectrum upon
electrogeneration of [4a]+-[4c]+. In ascending order of ꢀ at 650 nm: [4a]+,
[4b]+, [4c]+.
Prior reports of the UV/visible spectra of ruthenium(III)
acetylides have reported the presence of a similar LMCT
band, with vibronic structure of 1730-1830 cm-1 in the case
of [Ru(16-TMC)(CtCAr)2]+ 39 and of 2040-2050 cm-1 for
[Ru(CtCAr)2(dppe)2]30 on the high energy side of the band.
The LMCT bands seen on spectroelectrochemical generation
of [4b]+ and [4c]+ also contain some high energy structure,
which may be fitted to Gaussian curves with maxima at the
values shown in Table 3. The LMCT bands of [4a]+-[4c]+
are shown in Figure 6.
If the structure in the spectra of [4b]+ and [4c]+ is also
vibronic in origin, then the vibrational spacing ∆ν is 1223
and 1676 cm-1, respectively, a wide spread of values
somewhat lower than those previously reported. The values
are also lower than the vibrational frequency of the triple
bond involved ([4b]+ and [4c]+ have ν(CtC) of 1948 and
1959 cm-1, respectively (Table 3)), but it should be
remembered that the progression relates to the spacing in
the energy levels of the upper state of the transition. As the
LMCT transition involves moving an electron from an orbital
that is principally CtC π-bonding in character to one that
is principally metal dxy (Figure 5), the vibrational frequency
of the carbon-carbon bond in the excited state would be
lower than in the ground state, which would be reflected in
the spacing of the vibronic progression.
Luminescence Measurements
In view of the luminescent behavior of the geometrically
similar platinum compounds,2 a study of the photophysical
attributes of complexes 4a-c was undertaken. Measurements
were conducted on dichloromethane solutions at room
temperature, and excitation wavelengths were selected on
the basis of absorption spectra (Table 2). For all the
compounds 4a-c, excitation selectively into the MLCT
excited state (λexc ) 340, 470 nm) resulted in no observable
emission. In addition, the emissive properties of the com-
plexes were not significantly enhanced by utilizing the
aromatic chromophores; thus, in compounds 4a and 4b an
excitation wavelength of 260 nm (intraligand π-π*) resulted
(33) Lichtenberger, D. L.; Renshaw, S. K.; Bullock, R. M. J. Am. Chem.
Soc. 1993, 115, 3276-3285.
(34) McGrady, J. E.; Lovell, T.; Stranger, R.; Humphrey, M. G. Organo-
metallics 1997, 16, 4004-4011.
(35) Orpen, A. G.; Connelly, N. G. Organometallics 1990, 9, 1206-1210.
(36) Krivykh, V. V.; Eremenko, I. L.; Veghini, D.; Petrunenko, I. A.;
Pountney, D. L.; Unseld, D.; Berke, H. J. Organomet. Chem. 1996,
511, 111-114.
(37) Bianchini, C.; Laschi, F.; Masi, D.; Ottaviani, F. M.; Pastor, A.;
Peruzzini, M.; Zanello, P.; Zanobini, F. J. Am. Chem. Soc. 1993, 115,
2723-2730.
(38) Beddoes, R. L.; Bitcon, C.; Whiteley, M. W. J. Organomet. Chem.
1991, 402, 85-96.
(39) Choi, M.-Y.; Chan, M. C.-W.; Zhang, S.; Cheung, K.-K.; Che, C.-
M.; Wong, K.-Y. Organometallics 1999, 18, 2074-2080.
3498 Inorganic Chemistry, Vol. 43, No. 11, 2004

Diimine-Acetylide Compounds of Ruthenium
in no emission. Interestingly, under the same circumstances
the phenyl derivative 4c did show weak emission, at 463
and 526 nm.
redox-switchable charge-transfer transitions. However, unlike
platinum-diimine-bis(acetylide) compounds and lumines-
cent ruthenium-bipyridyl systems, compounds 4a-c are not
strongly emissive from fluid solution at room temperature.
Current work is focused upon synthesizing bis-acetylide
compounds from 4a-c; as these compounds are more similar
to emissive platinum species, it is hoped that they may
possess stronger fluorescence.
These unremarkable emissive properties therefore indicate
the presence of nonradiative decay pathways for 4a-c, in
contrast to related platinum(II) complexes which are brightly
emissive in solution at room temperature.2,5 It is worth noting
that chloride ions are known to quench fluorescence by
charge transfer from the halide to the excited state of a
chromophore, and the presence of free chloride (vide supra)
may be thus preventing emission from solutions of 4a-c.40
Acknowledgment. We wish to thank the University of
Bristol for a Junior Fellowship, Mr. Lifeng Zhu for the curve
fitting, and Professors A. G. Orpen and M. D. Ward and
Dr. S. Faulkner for helpful discussions.
Conclusions
The first series of ruthenium compounds with both
bipyridyl and acetylide ligands has been synthesized, and it
has been demonstrated that these compounds, 4a-c, have
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determination of 4a‚Et2O and
[4a][PF6]‚2.5thf. This material is available free of charge via the
Internet at http://pubs.acs.org.
(40) Goodall, W.; Williams, J. A. G. J. Chem. Soc., Dalton Trans. 2000,
2893-2895.
IC035181V
Inorganic Chemistry, Vol. 43, No. 11, 2004 3499