Abstract
Controlled intramolecular electron transfers were demonstrated in a series of cyanide-bridged Fe-Co molecular squares, [Co2Fe2(CN)6(L1)2(L2)4](PF6)2. The electronic structures of the molecular squares can be varied between [FeIIILS2CoIIHS2] and [FeIILS2CoIIILS2] state by intramolecular electron transfers, which were significantly affected by the redox potential differences between metal ions. Chemical modifications of the capping ligands allowed the systematic control of the electronic states, and the occurrence of a novel two-step thermal electron transfer-coupled spin transition (ETCST). The two-step ETCST was originating from three thermodynamically stable phases, LT, IM, and HT phases. The electronic structure of each phase was investigated by X-ray structural analyses, and the IM phase showed long-range order of [FeIIILS2CoIIHS2] and [FeIILS2CoIIILS2] species. In addition, novel thermal and protonation-induced ETCST in the solution state were found using variable temperature UV-vis absorption spectroscopy.
