Synthesis of a novel hydrogel based on a coordinate covalent polymer network

A new type of polymeric inorganic hydrogel is synthesized from the ligand substitution reaction of K[sub 2]PdCl[sub 4] by a cyanometalate such as K[sub 3]Fe(CN)[sub 6] in aqueous solution. These gels typically contain >95% water, as determined by thermogravimetric analysis. The Pd:Fe ratio is 2:1, independent of the stoichiometry employed, and two chloride ligands are displaced per palladium center. Infrared and electrochemical measurements indicate the presence of bridging cyanide ligands (i.e., Fe-CN-Pd), which lead to the formation of polymeric chains. Interchain cross-links are possible by a number of mechanisms. Dynamic oscillatory rheological measurements were performed during the sol-gel process. The effect of the reactant concentration, Pd:Fe ratio, and concentration of spectator ions on the gelation rate is discussed. 16 refs., 7 figs., 1 tab.