Spin Crossover in Anionic Cobalt-Bridged Fullerene (Bu4N+){Co(Ph3P)}2(µ2-Cl-)(µ2-η2,η2-C60)2 Dimers.

A spin crossover phenomena is observed in an anionic (Bu4N+){Co(Ph3P)}2(µ2-Cl-)(µ2-η2,η2-C60)2·2C6H14 (1) complex in which two cobalt atoms bridge two fullerene molecules to form a dimer. The dimer has a triplet ground state with two weakly coupling Co0 atoms (S = 1/2). The spin transition realized above 150 K is accompanied by a cobalt-to-fullerene charge transfer that forms a quintet excited state with a high spin CoI (S = 1) and C60•- (S = 1/2).