FeCNFe

FeCNFe is a shorthand used in inorganic chemistry to denote a dinuclear iron cyanide core in which two iron centers are linked by cyanide ligands, forming an Fe–CN–Fe motif. It occurs as a constituent unit in cyanide-bridged coordination compounds and in Prussian blue and related analogues, where such bridges help connect metal centers into extended lattices.

In these motifs, each iron center is typically octahedrally coordinated, sharing a cyanide carbon with the other iron. The oxidation states of the two irons vary with synthesis, but a common motif is Fe(III)–CN–Fe(II) in Prussian blue-type materials, enabling magnetic exchange between centers through the cyanide bridge.

Synthesis and occurrence: FeCNFe units can arise during assembly of cyanide-bridged materials from iron salts and ferro-/ferricyanide sources, under diffusion-controlled crystallization or hydrothermal conditions. They also appear as structural motifs within larger coordination polymers and metal–organic frameworks.

Properties: The cyanide bridge provides superexchange pathways that influence magnetic behavior, often yielding antiferromagnetic or ferrimagnetic interactions depending on oxidation state and geometry. Spectroscopic features include characteristic CN stretches near 2100 cm−1 in infrared spectra and intervalence charge-transfer bands in the visible region for mixed-valence systems.