A complexing approach to inducing sol-gel process of insoluble Cu ethoxide — evolution of local environment of Cu complex species

A stable gel was obtained from a methoxyethanol solution of Cu ethoxide using glacial acetic acid as a complexing agent with addition of water. Electron spin resonance, infrared and visible spectra of Cu complex species in solutions and gels were measured. The following results can be deduced from these spectra. (1) The structural characteristic of the primary Cu complex species in the methoxyethanol solution of Cu ethoxide with acetic acid (Cu/HOAC = 1:1) is a dimeric species, Cu2(OR)2(OAC)2(HOR)4, with small internuclear spacing and the same structure as that in crystalline hydrated copper acetate. (2) The primary Cu complex species transform to a hydrolyzed dimeric species, Cu2(OH)2(OAC)2(H2O)6, with large internuclear spacing through both hydrolysis and change in its coordination configuration. (3) The olation reaction occurs among the hydrolyzed species and finally results in the formation of a stable transparent gel. (4) The structural form of the hydrolyzed Cu complex species remains in fresh gel, while the structural form of Cu complex species in xerogel is similar to that of the primary Cu complex species.