Pressure-driven thermal spin transition behaviors in mono-nuclear iron(II) compounds: Synthesis, crystal structure and magnetic properties

Three isostructural mononuclear iron(II) complexes with the similar tripodal ligands had been synthesized and structurally characterized, which exhibit three-dimensional (3D) supramolecular network constructed by S···H―C hydrogen bonding interactions between adjacent iron centers. The variable-temperature magnetic properties of these three complexes under different pressure have been investigated to probe the possibilities of spin transition behavior under external pressure. For 1, the pressure-driven SCO behavior was firstly observed as the application of external pressure, and then the pressure-driven thermal SCO behavior occurs subsequently as the external pressure reached up to a specific value. However, for 2 and 3, no any SCO behaviors could be observed even under high external pressure. Comparison of the crystal structures of the three complexes show that the differences are mostly due to steric effects and weak ligand field originated from the similar tripodal ligands.