J. Phys. IV France 7 (1997) C2-659-C2-660
XAFS Analysis of Jahn-Teller Distortions in Tris(1,2-Diaminoethane)Copper(II) Sulfate Cu(en)3SO4F. Villain1, M. Verdaguer2 and Y. Dromzee2
1 Laboratoire pour l'Utilisation du Rayonnement Synchrotron, Université Paris Sud, 91405 Orsay, France
2 Laboratoire de Chimie des Métaux de Transition, URA 419 du CNRS, Université Pierre et Marie Curie, 4 place Jussieu, 75252 Paris, France
XAFS analysis Jahn-Teller distortions in tris(1,2-diaminoethane)copper(II) sulfate, Cu(en)3SO4 (en = 1,2- diaminoethane) shows that Cu(TI) is elongated octahedral at room and at low temperature: the XANES spectra are similar and the EXAFS signals are fitted with four short and two long Cu-N distances. This result is in apparent contradiction with X-ray diffraction studies: [Cu(en)3]2+ appears regular octahedral at 300 K and compressed at 120 K. The observed EXAFS is clearly incompatible with the EXAFS simulations using FEFF6 code, with the diffraction coordinates. On the contrary, a good agreement is obtained for the isostructural Ni(en)3SO4, where Ni is not subject to Jahn-Teller effect. Similar results are obtained with the hexanitrocuprate(II) K2PbCu(NO2)6 and the hexanitronickelate(II) K2PbNi(NO2)6. The results are in agreement with a dynamic Jahn-Teller effect in elongated octahedra [Cu(en)3]2+ and [Cu(NO2)6]4- at high temperature and with a static Jahn-Teller effect combined with an antiferrodistortive order at low temperature.
© EDP Sciences 1997