Eur. Phys. J. B 38, 541-552 (2004)
https://doi.org/10.1140/epjb/e2004-00150-9

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 claude.lecomte@lcm3b.uhp-nancy.fr

Received: 15 January 2004
Published online: 8 June 2004

Abstract

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 (Δd_Fe−NCS = −0.175(4) Å, Δd_Fe−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.