U. Koelle et al., MAGNETISM AND ELECTRONIC-STRUCTURE OF THE (PENTAMETHYLCYCLOPENTADIENYL)DICHLORORUTHENIUM DIMERS, Inorganic chemistry, 34(25), 1995, pp. 6273-6278
The unit cell of the binuclear Ru(III) 4d(5) (low spin, S = 1/2) compo
und [(C-5(CH3)(5)}Ru(mu-Cl)Cl](2) contains two isomers a and b which d
iffer distinctly in the Ru-Ru separation (2.93 Angstrom (a), 3.75 Angs
trom (b)) and in the Ru-Cl-Ru bridge angle (76 degrees (a), 100 degree
s (b)). Magnetic susceptibilities have been determined in the temperat
ure range 3 to 295 K in order to assess the intramolecular spin coupli
ngs. Isomer a shows a comparatively strong intramolecular antiferromag
netism (singlet-triplet splitting L 760 cm(-1)), whereas in b a weak f
erromagnetic coupling (triplet-singlet splitting approximate to 24 cm(
-1)) via the chlorine bridge is deduced. Extended Huckel calculations
provide a qualitative explanation for the observed geometries and spin
states of the two isomers. The electronic picture in these t(2g)(5)t(
2g)(5) compounds is very similar to that in the e(g)(3)e(g)(3) copper
dimers. Orbital crossing as a function of bridging angle leads to a ch
ange in spin state. The change in bonding character of the occupied or
bitals allows an understanding of the bond length differences seen in
the two isomers.