Abstract
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}2bpym] and tetranuclear [Fe(tpa){N(CN)2}]4·(BF4)4·(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.
Highlights
The term “spin transitions” joins two types of phenomena: spin crossover (SCO) [1]and charge-transfer-induced spin transitions [2] (CTIST)
The vibrational spectra of of molecular crystals contain along the phonons molecular crystals contain along the phonons the distinct branches of localized vibrations directly coupled to the electronic the distinct branches of localized vibrations directly coupled to the electronic shells of SCO ions
1) describing the interactions responsible for transpin sitions in molecular crystals can be presented by two types of springs with different force transitions in molecular crystals can be presented by two types of springs with different constants: the stiffer springspring corresponds to theto coupling of the of ions vibraforce constants: the stiffer corresponds the coupling thewith ionsmolecular with molecular tions, while the softer one describes the cooperative interaction through acoustic modes vibrations, while the softer one describes the cooperative interaction through acoustic between the structural units undergoing the spin modes between the structural units undergoing thetransition spin transition
Summary
The term “spin transitions” joins two types of phenomena: spin crossover (SCO) [1]. and charge-transfer-induced spin transitions [2] (CTIST). The vibrational spectra of of molecular crystals contain along the phonons (interrelated to intermolecular vibrations) molecular crystals contain along the phonons (interrelated to intermolecular vibrations) the distinct branches of localized (molecular) vibrations directly coupled to the electronic the distinct branches of localized (molecular) vibrations directly coupled to the electronic shells of SCO ions. 1) describing the interactions responsible for transpin sitions in molecular crystals can be presented by two types of springs with different force transitions in molecular crystals can be presented by two types of springs with different constants: the stiffer springspring corresponds to theto coupling of the of ions vibraforce constants: the stiffer corresponds the coupling thewith ionsmolecular with molecular tions, while the softer one describes the cooperative interaction through acoustic modes vibrations, while the softer one describes the cooperative interaction through acoustic between the structural units undergoing the spin [27]. Fe–Co compounds demonstrating iron(II) systems and in binuclear Fe–Co compounds demonstrating CTISTCTIST [24]. [24]
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