Magnetic exchange across the cyanide bridge

The superexchange interaction in cyano-bridged transition metal dimers is a nalysed by a valence bond configuration interaction model in combination wi th fourth order perturbation theory. Ferro- and antiferromagnetic contribut ions to the exchange splitting are expressed in terms of metal-ligand hybri dization matrix elements, metal-to-ligand, ligand-to-metal, metal-to-metal charge transfer energies, and intra-atomic exhange integrals. The formalism is simplified and we arrive at a two-parameter model, with which it is pos sible to estimate magnetic ordering temperatures of cubic stoichiometric Pr ussian Blue like phases containing first row transition metals. The relevan ce and applicability of our theoretical results is demonstrated on critical temperatures reported in the literature. The model accounts for both ferri - and ferromagnetic ordering temperatures. It is found that cyanide is an e fficient mediator of exchange due to the participation of the pi and pi* or bitals to equal extent.