Abstract: This invention relates to novel compositions of matter which are mixed metal metallo-organic complex agents comprised of a chemically united complex aluminum moiety and a tetravalent zirconium moiety. The specific process for preparing such compositions in organic/solvent media with desirable hydrolytic stability is described.Further described are compositions of matter wherein the aforementioned metallo-organics are employed to chemically modify the surface of fibrous and particulate inorganic substances and certain organic particulates, thereby resulting in hydrophobic, organophilic fibers and particles having improved rheological properties which facilitate higher filler (fiber) loading levels and serve to enhance the physical properties of composite articles and coatings formed therewith.