Approche structurale du phénomène de transition de Spin par diffraction des rayons X sous contraintes (T, P, hv)

Abstract

The spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeLn(NCS)2] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined.