The complex [Fe^II{(CN)Fe^IIIL⁵}₆]Cl₂ consists of a mixed-valence heptanuclear cyanide-bridged unit formed of a Schiff-base pentadentate ligand L⁵ and it shows a spin crossover of the peripheral Fe^III centres.

Different kinds of stimuli to induce spin crossover in iron compounds are covered, focusing on electromagnetic irradiation-induced spin state switching phenomena in mono- as well as multinuclear coordination compounds.

A mononuclear pentacoordinate iron(III) complex shows slow magnetic relaxation with three relaxation channels. The high-frequency relaxation time of the order of microseconds is prolonged on cooling in accordance with the direct and Raman processes. The low frequency relaxation time is little dependent on temperature and varies in the range τ(LF) = 0.52–0.79 s.