Application of the Heptacyanidorhenate(IV) as a Metalloligand in the Design of Molecular Magnets

This review is devoted to an analysis of currently known heterometallic molecular magnets based on an orbitally degenerate 5<i>d</i> metalloligand, [Re^IV(CN)₇]³⁻. Heptacyanidometallates with a pentagonal bipyramidal structure of the coordination site and degenerate ground spin state are the source of anisotropic magnetic exchange interactions upon the formation of cyanide-bonded assemblies involving the paramagnetic complexes of the first transition series. Therefore, the development of methods for chemical design using such molecular magnetic modules is extremely important. If for the 4d congener, isoelectronic [Mo^III(CN)₇]³⁻, a family of approximately 40 heterometallic compounds, was obtained, whereas for heptacyanorhenate(IV), no more than 20 are known. However, as a result of recent studies, heterobimetallic magnetic assemblies of all dimensionalities have been synthesized, from 0D to 1D, demonstrating slow magnetization relaxation, to 2D networks and 3D frameworks possessing large magnetic hysteresis. The most anisotropic is a 2D network, PPN[{Mn^III(acacen)}₂Re^IV(CN)₇]·Solv, with a critical temperature of 20 K and magnetic hysteresis with a record coercivity for cyanide-bridged molecular materials.