Tin Oxide Nanoparticles and SnO2/SiO2 Hybrid Materials by Twin Polymerization Using Tin(IV) Alkoxides

Twin polymerization was used to prepare composite materials composed of SnO2 nanoparticles entrapped in a polymer matrix. Novel, well-defined tin-containing molecular precursors, so-called twin monomers, were synthesized by transesterification starting from Sn(OR)(4) (R=tBu, tAm) to give Sn(OCH2C4H3O)(4) (1), [Sn(OCH2C4H3S)(4)HOCH2C4H3S](2) (2), [Sn(OCH2-2-OCH3C6H4)(4)HOCH2-2-OCH3C6H4](2) (3), [Sn(OCH2-2,4-(OCH3)(2)C6H3)(4)HOCH2-2,4-(OCH3)(2)C6H3](2) (4), 2,2-spirobi[4H-1,3,2-benzodioxastannine] (5), 2,2-spirobi[6-methylbenzo(4H-1,3,2)-dioxastannine] (6), and 2,2-spirobi[6-methoxybenzo(4H-1,3,2)dioxastannine] (7). C-13 and (SnNMR)-Sn-119 spectroscopy in the solid state and in solution as well as IR spectroscopy and elemental analysis were used to characterize the tin alkoxides. The molecular structures of compounds2 and 3 were determined by single-crystal X-ray diffraction analysis. The moisture sensitivity of the tin(IV) alkoxides was demonstrated by the formation of the tin oxocluster [Sn-3((3)-O)((2)-OH)((2)-OCH2C4H3S)(3)(OCH2C4H3S)(6)(HOCH2C4H3S)](2) (2a), a hydrolysis product of compound2. Polymerization reactions in the melt (for 1 and 5) and in solution (for 2-4) resulted in cross-linked nanocomposites of the type polymer/SnO2. Subsequent oxidation of the composites gave SnO2 with BET surface areas up to 178m(2)g(-1). Simultaneous twin polymerization of compounds5-7 with the silicon derivative 2,2-spirobi[4H-1,3,2-benzodioxasiline] resulted in the formation of polymer/SnO2/SiO2 hybrid materials. Oxidation gave porous materials with SnO2 nanoparticles embedded in a silica network with BET surface areas up to 378m(2)g(-1). The silica acts as a crystal growth inhibitor, which prevents sintering of the SnO2 nanoparticles 20-32nm in size.