ABSTRACTChanges 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 variations of the anion, dilution with Zn, under heating or the action of light. In all complexes, the spin transition is accompanied by drastic changes in the local environment of Fe atoms. The increase in spin transition temperature for the complexes with variable anions CIO4-, I-, Br-, BF4-, NO3- was found to correlate with changes in the Fe-N distances and changes in bond covalence determined from the chemical shifts in Mössbauer spectra. High spin metastable long life states were detected and studied in the polymeric complex Fe(atrz)3(ClO4)2. It was established that the changes in structure of polymeric complexes upon the transition to a metastable high spin state under the action of light differ from those in the thermally induced spin transition. Such differences are determined by mutual influence of Fe atoms in high spin and low spin states in polymeric chains.