Sol-gel processing of inorganic cyanogels

The reaction of aqueous solutions of K₂PdCl₄ and K_xM(CN)_n [where n=4 or 8 and M is a transition metal cation such as Fe(II/III), Co(II/III), Pd(II/IV), Pt(II/IV), V(II), Ru(II/III), Os(II/III), Au(III), or Mo(IV)] results in gel-like, 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 inorganic 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 at different temperatures between 200-500°C, under an inert atmosphere, produces new metastable materials, while sintering between 500-900°C produces ferromagnetic alloys. Processing under oxygen gives the mixed oxide material PbCoO₂, having the delafossite structure. As in the case of the palladium/cobalt system, thermal processing under an inert atmosphere leads to the formation of alloy systems. The cyanogels have been characterized using spectroscopic (UV-Vis, FTIR) and thermoanalytical methods (TGA, DSC, EGA-MS). X-ray powder diffractometry has been carried out on the thermal products associated with the palladium/cobalt system.