Heterobimetallic sol-gel precursors and intermediates

The question how the metals in bimetallic sol-gel materials are positioned relative to each other and how the dispersion of the metals can be controlled is a major preparative and analytical challenge. Two particular aspects are addressed: The first is an alternative type of single-source precursors where the two metals are interlinked through an organic spacer. The new options provided by this approach are demonstrated for metal oxide/silica nanocomposites, zinc titanate and Co3O4/ceria catalysts. The second issue with regard to heterobimetallic systems is the kind of intermediates formed during sol-gel co-processing of two different metal precursors (metal alkoxides or metal alkoxide + metal salt). Systematic investigation of the structures of Ti/M oxo clusters (M = main group or transition metal, or lanthanide) shows some interesting common construction principles and thus sheds light on early stages of the structural evolution in mixed-metal oxide systems. [GRAPHICS]