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 (FeSCO)-S-II effect.