Ar. Rezvani et al., INNER COORDINATION SPHERE CONTROL OF METAL-METAL SUPEREXCHANGE IN RUTHENIUM DIMERS, Inorganic chemistry, 36(15), 1997, pp. 3322-3329
The dinuclear Ru(III) complexes trans-[{(NH3)(4)Ru(py)}(2)(mu-L)][PF6]
(4), where py represents pyridine and L represents 1,4-dicyanamidobenz
ene dianion (dicyd(2-)) derivatives dicyd(2-) (1), Me(2)dicyd(2-) (2),
Cl(2)dicyd(2-) (3), and Cl(4)dicyd(2-) (4), have been prepared and ch
aracterized by electronic absorption spectroscopy and cyclic voltammet
ry. A crystal structure of the complex trans-[{(NH3)(4)Ru(py)}(2)(mu-d
icyd)][PF6](4) . 1/2H(2)O showed the dicyd(2-) ligand to be approximat
ely planar with the cyanamido groups in a syn configuration. Crystal s
tructure data are space group P2(1), with a, b, and c = 7.826(3), 20.4
55(7), and 14.428(5) Angstrom, respectively, beta = 95.76(3)degrees, V
= 2296.7(14) Angstrom(3), and Z = 2. The structure was refined by usi
ng 3292 reflections with I > 2.5 sigma(I) to an R factor of 0.069. Sol
id state magnetic susceptibility measurements of the Ru(III)-Ru(III) d
imers showed diamagnetic behavior at room temperature, and this is sug
gested to be due to strong antiferromagnetic superexchange via the HOM
O of the dicyd(2-) ligand. The bridging ligand dependence of metal-met
al coupling in the Ru(III)-Ru(II) complexes of 1, 2, 3, and 4 in aceto
nitrile solution was demonstrated by the trend in comproportionation c
onstants, 1.5 x 10(6), 5.7 x 10(6), 1.4 x 10(4), and 1.1 x 10(3), resp
ectively. In addition, comparison to the analogous pentaamminerutheniu
m dimers showed that the magnitude of metal-metal superexchange could
be controlled by the nature of the spectator ligand. Spectroelectroche
mical methods were used to acquire the absorption spectra of the mixed
-valence complexes, and the intervalence band properties were modeled
with PKS theory. Metal-metal coupling in the Ru(III)-Ru(II) complexes
of 1, 2, 3, and 4 was analyzed by using Hush and CNS theories.