Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure

J. Phys. IV France 7 (1997) C2-633-C2-635
DOI: 10.1051/jp4/1997124

Polymerie Fe(II) Spin Cross Over Compounds: XAS Structural Results

A. Michalowicz^{1, 2}, J. Moscovici¹ and O. Kahn<sup>3

1</sup>  Laboratoire de Physique des Milieux Désordonnés (LPMD), UFR des Sciences, Université Paris XII val de Marne, 61 avenue du Général De Gaulle, 94010 Créteil cedex, France
²  Laboratoire pour l'Utilisation de Rayonnement Électromagnétique (LURE), Université Paris sud, Bât. 209D, 91405 Orsay cedex France
³  Institut de Chimie de la Matière Condensée, Laboratoire des Sciences Moléculaires, Château de Brivasac, Avenue Albert Schweitzer, 33600 Pessac, France

Abstract
Fe(II)triazole derivatives are spin cross-over'compounds with various T_c (-30->+150 °C), large thermal hysteresis (ΔT_c = 50 K) and an important thermochromic effect. These promising properties, which are already used in experimental imaging and memory devices, are probably due to their polymeric structures. We have studied these structures by EXAFS and X-Ray diffraction (in spite of the important long distance disorder observed). The key result of this study is the alignment of a long chain of Fe(II) ions in the Low Spin (LS) state of the polymeric species, proved by the presence of a characteristic double Fe-Fe distance multiple scattering EXAFS signal (analysed by FEFF code). New results have been obtained recently on new members of the Fe(II) triazole family and nickel glyoxime model compounds presenting similar metal-metal alignment, proving definitely the assumed alignment in the LS state. Systematic study of the temperature dependence of the multiple-scattering signal amplitude were performed in order to explain the apparent vanishing of the alignment in the High Spin (HS) state.

© EDP Sciences 1997