Hot attraction in bimetals: A cyano-bridged vanadium-niobium bimetal assembly with a Curie temperature of 210 K

Cyano-bridged bimetal assemblies attract attention because of their magnetic properties such as photomagnetization, humidity-induced magnetization, and nonlinear magneto-optical effect, which make them suitable for many applications. A high Curie temperature is an asset for the use of such magnetic compounds in functional materials. Hexa-, hepta-, and octacyanometalates have been shown to have high Curie temperatures as a result of the high coordination number of their metal centers and the large superexchange interactions due to their diffuse 4d or 5d orbitals. Shin-ichi Ohkoshi and his co-workers at the University of Tokyo report the compound with the highest Curie temperature among octacyano-bridged bimetal assemblies in the Short Communication published in the European Journal of Inorganic Chemistry.

On the basis of initial studies indicating that an increased stoichiometry of vanadium(II) led to a higher Curie temperature in vanadium hexacyanochromate systems, Ohkoshi et al. used a small amount of V^III as catalyst to convert a higher proportion of V^II in a similar system. The magnetic properties of the resulting octacyano-bridged vanadium–niobium bimetal assembly were investigated. The compound, whose formula was determined to be K_0.59V^II_1.59V^III_0.41[Nb^IV(CN)₈] ·(SO₄)_0.50·6.9H₂O, is ferrimagnetic, and the spins on V^II and V^III are antiparallel with respect to the spin on Nb^IV. Its Curie temperature is 210 K. This high value is a result of the enhanced superexchange interaction through the V^II–NC–Nb^IV pathway.

This study reports a strategy to synthesize magnetic materials with high Curie temperature to enhance the suitability of their magnetic properties for applications.