Interplay of Jahn-Teller Ordering and Spin Crossover in Co(II) Compounds

Sophia Klokishner,Serghei M Ostrovsky

doi:10.3390/magnetochemistry6040062

Sophia Klokishner, Serghei M Ostrovsky

Open Access

https://doi.org/10.3390/magnetochemistry6040062

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Abstract

The spin crossover phenomena in Co(II) compounds are in the focus of the present paper. A microscopic theoretical approach for the description of spin transitions in mononuclear Co(II) compounds is suggested. Within the framework of this approach there are taken into account two types of interionic interactions that may be operative in the problem such as the electron-deformational interaction and the cooperative Jahn-Teller interaction arising from the coupling of the low-spin state of the Co(II) ion with the tetragonal vibrations of the nearest surrounding. The different role of these interactions in the spin transformation is demonstrated and discussed. On the basis of developed approach a qualitative and quantitative explanation of the experimental data on the temperature dependence of the magnetic susceptibility for the [Co(pyterpy)2](PF6)2, [Co(pyterpy)2](TCNQ)2⋅DMF⋅MeOH and [Co(pyterpy)2](TCNQ)2⋅MeCN⋅MeOH compounds is given.

Highlights

Since the moment of the discovery of the phenomenon of spin crossover (SCO) the overwhelming majority of research in the field mainly deals with the experimental and theoretical study of iron(II) compounds [1]
Basing on this one can assume that in iron(II) compounds the deformation which arises from the ls- hs transition on the account of the expansion of the electronic shell is mainly a full symmetric one, and the coupling of the spin crossover iron(II) ions with the tetragonal or trigonal deformations plays a secondary role in the spin transition in these compounds
In paper [3] the investigations of a cobalt(II) clathrochelate complex, which nearly does not change the molecular volume during the spin transformation, demonstrated that even weak intermolecular interactions can cause a pronounced anticooperativity of spin crossover, which results in a more gradual transition in the solid state than in solution

Summary

Introduction

Since the moment of the discovery of the phenomenon of spin crossover (SCO) the overwhelming majority of research in the field mainly deals with the experimental and theoretical study of iron(II) compounds [1]. Such a conclusion follows from the study performed in the paper [2] in which it has been obtained that the space group in the examined Fe(II) compounds does not change with temperature Basing on this one can assume that in iron(II) compounds the deformation which arises from the ls- hs transition (ls—low-spin) on the account of the expansion of the electronic shell is mainly a full symmetric one, and the coupling of the spin crossover iron(II) ions with the tetragonal or trigonal deformations plays a secondary role in the spin transition in these compounds.

The Model

Estimation of the Characteristic Parameters of the System

Results and Discussion