Thermoinduced Metal‐to‐Metal Charge Transfer in Trinuclear Metal String Complex Ru2M(dpa)4Cl2 (M=Ni, Cu, dpa=Dipyridylamido)

Abstract

AbstractThe vibrational and electronic structures of diruthenium nickel and copper complexes [Ru2Ni(dpa)4Cl2]0,1+ and [Ru2Cu(dpa)4Cl2]0,1+ were studied by using temperature‐controlled Raman spectroscopy and density functional theory (DFT) calculations. In the neutral species, the Ru−Ru stretching mode νRu−Ru was assigned to the 333/325 cm−1 band for the diruthenium Ni/Cu complexes, and this band greatly red shifted to 317/321 cm−1 at high temperatures. In contrast, this νRu−Ru band showed no shift in the oxidized forms. The time‐dependent DFT (TD‐DFT) calculations yielded that these complexes in the neutral form, have [Ru2]5+[M]1+ cores with [Ru2] moiety configuration (π*)2(δ*)1 and two low‐lying electronic excited states with [Ru2]4+[M]2+ cores and [Ru2] configurations of (π*)2(δ*)2 and (π*)3(δ*)1, respectively. The significant red shift of νRu−Ru band was explained to thermally access to these two excited states which have [Ru2]4+ cores and weak Ru−Ru bonding. These two states were resulted from metal‐to‐metal intramolecular charge transfer processes from [Ru2]5+[Ni/Cu]1+ to [Ru2]4+[Ni/Cu]2+. This charge transfer reaction is prohibited in the oxidized form.