Electronic Coupling in Mixed-Valence Dinuclear Ferrocenes and Cobaltocenes with Saturated Bridging Groups



We have synthesised a series of new dinuclear metallocenes [{M(Cp*)(C5H4)}2X] (Cp*=η5-pentamethylcyclopentadienyl; M=Fe, Co, X=CMe2, SiMe2, GeMe2; M=Fe, X=Si2Me4). For the neutral dicobalt complexes, magnetic susceptibility measurements reveal intramolecular antiferromagnetic interactions of −21 and −14 cm−1 for SiMe2- and GeMe2-bridged species, respectively, but negligible interaction for the CMe2-bridged compound. In contrast, intervalence charge-transfer (IVCT) data for the mixed-valence monocations of both Fe and Co complexes show electronic coupling to decrease in the order CMe2>SiMe2>GeMe2. This suggests that electronic coupling is principally through-space in contrast to results found from previous studies. The IVCT data also show much stronger coupling in the dicobalt species versus their diiron analogues.