EXAFS study of spin transition effect on the spatial and electronic structure of Fe(II) complexes with triazoles

EXAFS spectroscopy is used to investigate the characteristic features of the spatial and electronic structure of the polynuclear Fe(II) complexes Fe(ATR)(3)A(2) (where A is the NO3-, BF4-, Br-, or ClO4- anion and ATR is 4-amino-1,2,4-triazole) and their magnetically diluted phases FexZn1-x(ATR)(3)(NO3)(2). The absolute distances from Fe and Zn to the surrounding atoms are determined at temperatures higher and lower than the spin transition point. In all complexes, the spin transition is accompanied by significant changes in the local environment of Fe atoms, while in the magnetically diluted phases the surrounding of zinc remains unchanged. It is shown that addition of Zn atoms distorts the triazole rings in the low-spin state of the complexes. No localized anions were revealed within 3.3 Angstrom from the Fe and Zn atoms. It is shown that a decrease in the spin transition temperature correlates with an increase in Fe-N distances in the low-spin complexes due to magnetic dilution and substitution of anions in the series NO3-, BF4-, Br-, ClO4- of ATR-containing complexes.