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^II spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3‐CNpy)₂][Re(CN)₈]}?H₂O ( 1 ) (3‐CNpy=3‐cyanopyridine) assembly consisting of cyanido‐bridged Fe^II‐Re^V square grid sheets bonded by Cs⁺ ions. The presence of two non‐equivalent Fe^II sites and the conjunction of 2D bimetallic coordination network with non‐covalent interlayer interactions involving Cs⁺, [Re^V(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 Fe^II state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable Fe^II SCO effect.