Octacyanidorhenate(V) Ion as an Efficient Linker for Hysteretic Two-Step Iron(II) Spin Crossover Switchable by Temperature, Light, and Pressure.

We report the two-step hysteretic Fe(II) spin crossover (SCO) effect achieved in programmed layered Cs{[Fe(3-CNpy)2] [Re(CN)8]}·H2O (1) assembly consisting of cyanido-bridged FeII-ReV square grid sheets bonded by Cs+ ions. The presence of two non-equivalent FeII sites and the conjunction of 2-D bimetallic coordination network with non-covalent interlayer interactions involving Cs+, [ReV(CN)8]3- ions, and 3-CNpy ligands, leads to the occurrence of two steps of thermal SCO with strong cooperativity giving a double thermal hysteresis loop. The resulting spin transition phenomenon could be tuned by an external pressure giving the room temperature range of SCO as well as by visible light irradiation inducing an efficient recovery of the high spin FeII state at low temperatures. In this report, we prove that octacyanidorhenate(V) ion is an outstanding metalloligand for inducing of cooperative multi-step, multi-switchable FeII SCO effect.