Temperature and pressure dependent single crystal neutron diffraction of Fe(pmd)2[Ag(CN)2]2 (pmd=pyrimidine)

Abstract

The combination of two or more properties in the same material to investigate possible interplay and synergy between them has been a singular topic of the scientific investigations nowadays. To move towards applications, one of the most promising fields is that of the switchable magnetic materials, which under different external perturbations, like temperature, light, pressure, electrical and magnetic fields, undergo drastic changes of their physical properties. Their molecular bistability can be therefore used to switch a second physical property. Spin crossover (SCO) compounds are particularly well adapted to this strategy since the spin state can be switched in a controlled manner between a low spin (LS) and high spin (HS) state involving magnetic, optical and structural changes stimulated by the action of temperature, pressure or light. Although much work has been done in this field, the subject of pressure dependent crystal structure determinations in SCO compounds is practically unexplored. Here we focus in the structure of Fe(pmd)2[Ag(CN)2]2 (pmd= pyrimidine) complex, that can be depicted as (4,4)-layers, where each Fe(II) atom is linked to four [Ag(CN)2]- anions which run parallel to the ac-plane. These planes are connected through the pmd ligands to the adjacent ones, constructing the final 3D structure. This compound is very sensitive to temperature and pressure, and undergoes a cooperative high-spin low-spin effect. Neutron diffraction studies with low temperature and high pressure have been performed at the VIVALDI instrument at ILL in order to obtain the crystal structure of the different pressure and temperature induced phases of the sample. The present work contributes to enlarge the short series of examples of structural studies under high-pressure reported up to now in SCO compounds.