Crystal structures of hexacyanometallates with bifurcated cyano groups

Abstract

The crystal structures for T2[M(CN)6] where T = Mn, Cd; M = Fe, Ru, Os, were refined from the corresponding XRD powder patterns using the Rietveld method in the hexagonal P-3 (147) space group with Z = 1. In the structure of these families of anhydrous hexacyanometallates (II) the N end of the CN group appears bifurcated, serving as a ligand for two neighbouring T metals. Such a coordination mode has not been reported before for transition metal hexacyanometallates but it is consistent with the magnetic properties and Mössbauer, IR and Raman spectra of the studied compounds. The anhydrous solids are obtained by dehydration of the corresponding octahydrates. In the hydrated form the metals (Mn, Cd) linked at the N ends have a mixed coordination sphere formed by three N atoms and three coordinated waters, with two of these latter forming bridges between two neighbouring metals. The loss of these structural waters leaves the metals (T) in an unstable state with only three ligands in their coordination sphere and a structural transformation involving a change in the CN group electronic configuration is induced. The metal coordination through bifurcated CN groups leads to a remarkable increase in the charge overlapping between the metal centres, which appears attractive for molecular magnet design.