Crystalline hybrid organic–inorganic alumino-silicates

The synthesis and the physico-chemical characterization of hybrid organic–inorganic crystalline phases referred to as ECS (Eni Carbon Silicate), constituting a new family of organic–inorganic hybrid materials, are described. ECS phases were synthesized in basic medium using 1,4-bis-(triethoxysilyl)-benzene (BTEB), 4,4′-bis-(triethoxysilyl)-biphenyl (BTEBP), 1,4-bis-(2-triethoxysilyl-ethyl)-benzene (BTEEB), 1,3-bis-(trimethoxysilyl)-propane (BTMP) as silica sources, NaAlO2 as source of alumina and an alkali metal hydroxide (NaOH or KOH). Among the bis-silylated organic precursors, BTEB proved to be the most versatile, since three different crystalline phases (ECS-1 to ECS-3) were obtained by changing the synthesis parameters. The presence of Al is in each case critical, since no crystalline products were obtained without NaAlO2. The solid products were deeply characterized by XRD, HRTEM, 29Si, 27Al and 13C MAS NMR, porosimetry, elemental and thermogravimetric analyses. For one of them, ECS-2, the crystal structure was determined and refined starting from the high resolution synchrotron powder diffraction data. It consists of inorganic layers linked by the phenylene groups and built up by [AlO4] and [SiO3C] tetrahedra.