The effect of axial ligands on the structure, oxidation state, and
electronic configuration of two diruthenium(II,III) and two diruthenium(III,III) complexes is reported.
The investigated compounds are represented by
Ru2(dpf)4Cl (1),
Ru2(dpf)4(C⋮CC6H5)
(2),
Ru2(dpf)4(C⋮CC6H5)2
(3), and
Ru2(dpf)4(CN)2
(4), where dpf is the
N,N‘-diphenylformamidinate ion. The chloro
and mono(phenylacetylide) complexes, which contain a
Ru2
5+ core,
are paramagnetic and contain three unpaired electrons, while the
bis(phenylacetylide) and bis(cyano) species,
which contain a Ru2
6+ core, are diamagnetic.
Compound 1, Ru2(dpf)4Cl,
was prepared by heating
Ru2(CH3COO)4Cl
and excess molten N,N‘-diphenylformamidine (Hdpf)
for 10 h at 130 °C under an argon atmosphere.
Compound
2,
Ru2(dpf)4(C⋮CC6H5),
was prepared by reaction of purified
Ru2(dpf)4Cl with
LiC⋮CC6H5 (in a 1:5 ratio) in
THF at room temperature (2 h). Compound 3,
Ru2(dpf)4(C⋮CC6H5)2,
was also obtained from Ru2(dpf)4Cl
by
using excess LiC⋮CC6H5. A related
diruthenium(III,III) complex,
Ru2(dpf)4(CN)2
(4), was also synthesized in
order to determine whether the observed octahedral distortion in
3 was due to electronic or steric effects.
Ru2(dpf)4(CN)2 was prepared by
reaction of Ru2(dpf)4Cl and a large excess
of NaCN in THF at room temperature
(10 h). All four compounds were isolated and characterized by
single-crystal X-ray diffraction, 1H NMR,
13C
NMR, IR, and UV−visible spectroscopy, and mass spectrometry, as well
as by electrochemistry. Compound 1
crystallizes in the tetragonal space group
P4/ncc, with a = 14.837(2) Å,
c = 21.599(5) Å, and Z = 4,
while
compound 2 belongs to the monoclinic space group
I2/c, with a = 18.590(5) Å,
b = 30.913(12) Å, c =
17.360(4)
Å, β = 93.61(2)°, and Z = 8. The magnetic
moments of the two diruthenium(II,III) species, 1
and 2, are 3.89
and 3.87 μB, respectively, in the solid state at 297 K,
consistent with three unpaired electrons and an electronic
configuration of
(σ)2(π)4(δ)2(δ*π*)3.
Compounds 3 and 4 are diamagnetic in their
neutral form but paramagnetic
upon controlled-potential reduction by one electron. The two
reduced RuIIRuIII species,
[Ru2(dpf)4(C⋮CC6H5)2]-
and
[Ru2(dpf)4(CN)2]-,
were characterized by ESR spectroscopy after electrochemical generation
and display a
rhombic signal whose shape is consistent with the presence of only a
single unpaired electron. Compound 2,
which contains three unpaired electrons, gives a bis adduct
Ru2(dpf)4(C⋮CC6H5)(CNCH2C6H5)
upon addition of
excess CNCH2C6H5 to the solution of
Ru2(dpf)4(C⋮CC6H5).
The bis adduct species has only one single unpaired
electron and shows an ESR spectrum similar to that of electroreduced
[Ru2(dpf)4(C⋮CC6H5)2]-
and
[Ru2(dpf)4(CN)2]-.
Crystals of 3 and 4 belong to the monoclinic
space groups C2/c and P21,
with a = 35.322(7) Å, b =
15.163(3)
Å, c = 31.820(9) Å, β = 93.59(2)°, and
Z = 12 (compound 3) and with a
= 16.184(4) Å, b = 15.784(3) Å,
c
= 12.896(3) Å, β = 112.29 (2)°, and Z = 2
(compound 4). The Ru−Ru bond distances of
1 and 2 are in the
expected range for diruthenium(II,III) co...
