Molecule-based magnetic nanoparticles: Synthesis of cobalt hexacyanoferrate, cobalt pentacyanonitrosylferrate, and chromium hexacyanochromate coordination polymers in water-in-oil microemulsions

Although considerable effort has been dedicated to the controlled synthesis of nanoparticles with classical inorganic structures, there are few reports on the formation of nanoscale materials based on supramolecular compounds such as transition metal coordination polymers. Here we describe the synthesis of crystalline nanoparticles of three different molecule-based magnetic materials, cobalt hexacyanoferrate, cobalt pentacyanonitrosylferrate, and chromium hexacyanochromate, by coprecipitation reactions involving mixtures of water-in-oil microemulsions. The cobalt-containing nanoparticles are regular in shape and size and have dimensions between 12 and 22 nm depending on the concentration of the reactants trapped within the water droplets. At sufficiently high particle concentrations, superlattice structures are formed by solvent evaporation. Growth of the nanoparticles occurs by interdroplet aggregation of primary clusters that are nucleated in the confined spaces of the microemulsion reaction field.