The structural characterization and physical properties of [Cp*M(pentalene)M'Cp*](n+) (Cp* = pentamethylcyclopentadiene; M, M' = Fe, Fe (1a); Co, Co (1b); Ni,Ni (1c); Ru, Ru (1d); Fe, Ru (1e); Fe; Co (if); n = 0, 1,2) and [Cp*M(s-indacene)M'Cp*](n+) (s = symmetric) and [Cp*M(as-indacene)M'Cp*](n+) (M, M' = Fe, Fe (2a, 3a); Co, Co (2b, 3b); Ni, Ni (2c, 3c); n = 0, 1, 2) (as = asymmetric) are reported. The local molecular structure of the organometallic complex does not change significantly with oxidation state; in all cases the Cp*M moieties reside on opposite faces of the fused mu-bridging ring systems, reflecting the dominance of steric effects. These complexes generally exhibit behavior consistent with significant electronic interactions between metal centers, including large electrochemical potential separations between successive one-electron redox events, and for the mixed valent (n = 1+) complexes, intervalent charge transfer absorption bands. The magnetic susceptibility data are consistent with intramolecular ferromagnetic coupling of spins for 1a(2+) and 2c(2+) and antiferromagnetic coupling of spins for 1c, 1c(2+), 1b, 2b, 1c(+), 2c(+), and 3c(+). In general, the paramagnetic complexes exhibit Curie-Weiss behavior, except for 2c and 3c, which possess singlet ground states and high spin excited states that are 0.036 and 0.056 eV (290 and 524 cm(-1)) above the ground state, respectively. Mixed-valent 1a(+) and 2a(+) are fully detrapped on the Mossbauer time scale (i.e., electron transfer rates, greater than or equal to 10(7) s(-1)) above 1.5 K, consistent with a negligible energy barrier to intramolecular electron transfer or complete delocalization. The EPR spectra of 1a(+), 2a(+), and 1e(+) exhibit significantly reduced g-factor ansiotropies and more intense spectral features at ambient temperature:compared to [FeCp*(2)](.+), implying intramolecular electron transfer rates greater than or equal to 10(10) s(-1).
