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) comp lexes Fe(ATR)(3)A(2) (where A is the NO3-, BF4-, Br-, or ClO4- anion a nd ATR is 4-amino-1,2,4-triazole) and their magnetically diluted phase s FexZn1-x(ATR)(3)(NO3)(2). The absolute distances from Fe and Zn to t he surrounding atoms are determined at temperatures higher and lower t han the spin transition point. In all complexes, the spin transition i s accompanied by significant changes in the local environment of Fe at oms, 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 an ions were revealed within 3.3 Angstrom from the Fe and Zn atoms. It is shown that a decrease in the spin transition temperature correlates w ith an increase in Fe-N distances in the low-spin complexes due to mag netic dilution and substitution of anions in the series NO3-, BF4-, Br -, ClO4- of ATR-containing complexes.