Influence of the interaction of polymeric chains on thermal transitions of Jahn—Teller exchange clusters in compounds of "breathing" crystal family

Based on the method of random field distribution functions in Ising magnets, for the first time a theoretical description of thermal transitions in Jahn—Teller exchange clusters is suggested, which takes into account the interactions of polymeric chains in "breathing" crystal compounds. It was shown that the inclusion of this interaction can lead to both an intensification of spin-crossover type cooperative transitions in exchange clusters and their deceleration. The approach in question is generalized to include non-Jahn—Teller metal impurities in "breathing" crystals, which suppress cooperative effects in thermal transitions of Jahn—Teller exchange clusters. The obtained results qualitatively reproduce the temperature dependencies of magnetic properties of solid solutions Cu_1—xNi_x(hfac)₂L^R (hfac is hexafluoroacetylacetonate anion, ligand L^R is nitronyl nitroxide radical with pyrazole substituent at the second position of the imidazoline ring) when R = Et.