Bukin G. Pressure-induced high spin - low spin transitions of Fe2+ ions in coordination compounds

The dissertation is dedicated to experimental study of pressure-induced spin transitions at room temperature in a series single-nuclear of coordination compounds of different dimension with Fe(II) ions, such as: model compound Fe(phen)2(NCS)2 polymorph II; 3D polymers [Fe(pmd)(H2O)[M(CN)2][Mg(CN)2]]·H2O (pmd = pyrimidine, M is connecting metals Ag and Au); a group of isostructural 2D compounds Fe(3-Fpy)2[M(CN)4] (3-Fpy = halogenous derivatives of pyridine, M is connecting metals Ni, Pd and Pt). For the first time, complete spin transitions with piezo hysteresis have been induced by pressure at room temperature for a series of coordination compounds containing Fe(II) ions. Using experimental data for temperature-induced spin transitions under pressure for all studied compounds, the parameters of interaction between high-spin complexes and elastic energy have been defined in the frames of elastic interactions approach. The pressure of the pressure-induced spin transition, not always coincides with pressure of the temperature-induced spin transition. It is shown that enthalpy variations at pressure-induced spin transitions correspond to enthalpy variations at temperature-induced spin transitions at constant pressure if the transition pressures coincide. Dependence of change of the temperature transition at change of pressure for the temperature-induced transitions is qualitatively described by modified equation Klapeyron-Klauzius taking into account change of elastic energy and energy of interaction under pressure.