Spin transition in iron(II) polymeric complexes and their structure at equilibrium and metastable spin states

Changes in the electronic and spatial structure of polymeric Fe(II) complexes with 1,2,4-triazoles and various anions upon spin transition was studied using EXAFS and XANES spectroscopy. Spin transition and structural changes were induced by the change of temperature or the action of light. In all complexes, the spin transition is accompanied by drastic changes in the local environment of Fe atoms. The existence of long-life optically excited metastable HS states was revealed for the Fe(atrz)3(ClO4)2 at 4.2 K. It was established that the changes in structure of polymeric complex under the action of light at 4.2 K differ from those in the thermally induced spin transition. Such type of differences are determined by mutual influence of neighboring Fe atoms in high and low spin states in polymeric chains.