Single crystal diffraction analysis of the thermal spin conversion in [Fe(btr)2(NCS)2] (H2O): evidence for spin-like domain formation
Laboratoire de Cristallographie et Modélisation des Matériaux
Minéraux et Biologiques, Université Henri Poincaré, UMR CNRS 7036, 54506 Vandœuvre les Nancy, France
Corresponding author: a email@example.com
Published online: 8 June 2004
The structural properties of the spin crossover compound [ Fe(btr)2(NCS)2] (H2O), where btr stands for 4,4'-bis-1,2,4-triazole, are investigated by single crystal X-ray diffraction at different temperatures in the thermal spin transition regime. The 104.0([see full textsee full textsee full text]) K low spin (LS) crystal structure is compared to the room temperature high spin (HS) crystal structure. The C2/c space group is retained in the LS state with an abrupt anisotropic shortening of the b and c cell parameters and a lengthening of a at the transition temperature. The major structural modifications related to the spin transition are a shortening of the Fe-N bond lengths (ΔdFe−NCS = −0.175(4) Å, ΔdFe−N(btr) = −0.213(3) Å) and a reorientation of the NCS groups with a more linear Fe-N-C-S geometry on going from HS to LS. Diffraction measurements have also been performed at 124 K on a trapped mixed spin state. The observed diffraction pattern shows the coexistence of two crystal lattices corresponding to ordered LS and HS species, which is a direct evidence of spin-like domain formation during the transition. The corresponding fraction of HS species () has been determined by structural refinement using several reference temperature measurements. To investigate dynamical aspects, X-ray data were collected versus time during the spin transition at constant temperature (T=117.2(2) K). No evidence has been found for any putative presence of an intermediate structural state during the spin transition.
PACS: 75.30.Wx – Spin crossover / 61.50.Ks – Crystallographic aspects of phase transformations; pressure effects / 61.10.Nz – X-ray diffraction
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2004