Manganese hexacyanomanganate: Magnetic interactions via cyanide in a mixed valence Prussian blue type compound

A Prussian blue type compound of the stoichiometric composition Mn(CN)₃ṡxH₂O (x=0.57) is formed as the final product of hydrolysis of Na₃[Mn(CN)₆] in perchloric acid. IR and visible spectra as well as structural and magnetic data show that it is a mixed valence compound consisting of sixfold N-coordinated Mn(II) and sixfold C-coordinated Mn(IV) in a cubic face-centered lattice. The compound exhibits ferrimagnetism with a Curie temperature of 48.7 K. A molecular field treatment assuming two collinear spin sublattices provides an adequate description of the observed magnetic behavior. The calculation of exchange integrals, which was based on a Heisenberg model, reveals that the magnetic ordering is almost exclusively induced by an antiferromagnetic interaction between Mn(II) and Mn(IV) ions. This interaction is described in terms of a super exchange involving cyanide as bridging ligand.