Cooperative Spin Transitions Triggered by Phonons in Metal Complexes Coupled to Molecular Vibrations

The present article is a short overview of the theoretical modeling of spin transitions in polymetallic compounds. As distinguished from many insightful reviews on this topic, the present work is focused on the nature of cooperative interaction of the metal clusters in molecular crystals with emphasis at the physical role of molecular vibrations and phonons. The underlying model assumes that the cooperativity is triggered by phonons while the metal centers are coupled to molecular vibrations. It is demonstrated that the suggested model gives a satisfactory description of the observed spin transitions in mono-, bi- and tetranuclear compounds. In the framework of the described approach, we discuss the experimental data on spin crossover in the mononuclear [Fe(ptz)(6)](BF4)(2), binuclear [{Fe(bt)(NCS)(2)}(2)bpym] and tetranuclear [Fe(tpa){N(CN)(2)}](4)center dot(BF4)(4)center dot(H2O)(2) compounds containing iron ions. The approach is also applied to the description of the charge-transfer-induced spin transition in the [{(Tp)Fe(CN)(3)}{Co-(PY5Me2)}](CF3SO3) complex.