Structural phase transition in the spin-crossover complex [Fe(ptz)₆](BF₄)₂ studied by x-ray diffraction

Sabine Lakhloufi (1) , Philippe Guionneau (1) , Marie-Hélène Lemée-Cailleau (2) , Patrick Rosa (1) , Jean-François Letard (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 ILL - Institut Laue-Langevin

The spin-crossover system [Fe(ptz)₆](BF₄)₂ has been studied for more than 25 years and is used as a model system to the understanding of the eponymous phenomenon in solid-state materials. However, the structural properties of the low-spin phase formed at low temperature after a slow cooling have never been elucidated due to a splitting of the Bragg peaks. We report here a reinvestigation of this low-spin phase by single-crystal x-ray diffraction. This study demonstrates the perfect matching between the structural and magnetic transitions temperatures and hysteresis width through careful unit-cell temperature dependence. The Bragg splitting is also unambiguously associated to the spin transition. Above all, this work reveals a reversible doubling of the unit-cell parameters a and b corresponding to the spin transition. A preliminary solution for the crystal structure of the low-spin phase notably shows the potential major role of the deformation of the n-propyl groups in the physical behavior of this material.

Mots clés: Spin crossover; Phase transition; X-ray diffraction; Inorganic compounds

Domaines: Matériaux

Sabine Lakhloufi, Philippe Guionneau, Marie-Hélène Lemée-Cailleau, Patrick Rosa, Jean-François Letard. Structural phase transition in the spin-crossover complex [Fe(ptz)₆](BF₄)₂ studied by x-ray diffraction. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2010, 82 (13), pp.132104. ⟨10.1103/PhysRevB.82.132104⟩. ⟨hal-00545047⟩