Use of Sol-Gel Chemistry for the Preparation of Cyanogels as Ceramic and Alloy Precursors

The reaction of aqueous solutions of K₂PdCl₄ and K₃Co(CN)₆ results in gellike polymeric materials, characterized by bridging cyanides between the central metals of the adducts. These materials tend to be rigid in nature but contain in excess of 95% water by weight. We refer to these novel transition metal based hydrogels as cyanogels. In contrast to classic inorganic hydrogels these materials are not based on an oxide network. Dehydration of the cyanogels results in amorphous xerogels which maintain the initial polymeric structure of the cyanogel. Thermal processing of gels containing palladium and cobalt centers under an inert atmosphere at temperatures between 200 and 500 °C, produces a new metastable material. Sintering between 500 and 1000 °C produces ferromagnetic alloys, while processing under oxygen in the same temperature region gives the ceramic mixed oxide material PbCoO₂, having the delafossite structure.