Synthetic strategy and structures of [Cr(CN)6]3−, [Mo(CN)8]3− and [W(CN)8]3− bridged di- and poly-nuclear transition metal-salen complexes: A review

•Literature shows many metallocyanate bridged metal-salen complexes.•Only the metallocyanates of group-VI are considered in this review.•Syntheses and structures of these complexes are highlighted in this review.•Their magnetic properties and applications as magnetic material are also discussed.•Only X-ray characterized complexes are considered in this review. The cyanide groups of [Cr(CN)6]3−, [Mo(CN)8]3− and [W(CN)8]3− may be used to bridge several mono-nuclear transition metal-salen complexes to form different di-, tri-, tetra- hexa- and poly-nuclear complexes of different molecular architectures. The synthetic strategy of the complexes generally involves the formation of H2salen type ligands by the 1:2 condensation of the appropriate diamine and salicylaldehyde derivatives in appropriate solvent at the beginning, followed by the formation of mononuclear transition metal-salen complexes, which are finally connected by [Cr(CN)6]3−, [Mo(CN)8]3− and [W(CN)8]3− bridges to form poly-nuclear complexes. In some cases, however, transition metal-salen units were not isolated, but they have been used in situ to synthesize cyanide bridged poly-nuclear complexes. The magnetic properties of these complexes are interesting. This review represents an overview on the synthetic strategies, structures, magnetic properties of these complexes. It is noteworthy that only those complexes are considered in this review whose X-ray structures are available.