Interplay Of Jahn-Teller Ordering And Spin Crossover In Co(Ii) Compounds

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)center dot DMF center dot MeOH and [Co(pyterpy)(2)](TCNQ)(2)center dot MeCN center dot MeOH compounds is given.