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

A two-step hysteretic Fe spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3-CNpy) ][Re(CN) ]}⋅H O (1) (3-CNpy=3-cyanopyridine) assembly consisting of cyanido-bridged Fe -Re square grid sheets bonded by Cs ions. The presence of two non-equivalent Fe sites and the conjunction of 2D bimetallic coordination network with non-covalent interlayer interactions involving Cs , [Re (CN) ] 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 Fe state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable Fe SCO effect.