Synthesis, characterization and crystal structure of new microporous bismuth silicates

The hydrothermal synthesis and structural characterization of two new microporous bismuth silicates named EMS-4 and EMS-5 are reported. The crystal structure of these materials has been elucidated by high-resolution synchrotron X-ray powder diffraction data and further characterized by chemical analysis, thermogravimetry and scanning electron microscopy.The crystal structure of EMS-4 is strictly related to that of the mineral tobermorite 11 Å which can be described by infinite layers formed by six- and sevenfold-coordinated metal polyhedra, held together by tetrahedral double chains. This stacking arrangement produces a relatively wide channel system able to host cations (sodium and potassium) and water molecules.EMS-5, the silicon counterpart of Bi2Ge3O9, can be classified as a clathrate-like structure having small cages with approximate dimensions 4.0 × 4.2 × 2.2 Å. Although the tetramethylammonium hydroxide (TMA-OH) has been used as structure directing agent in the synthesis, no organic or water molecules are localized inside the EMS-5 cages by the crystal structure refinement. This finding is also confirmed by TG and IR analyses.EMS-4 and EMS-5 materials are the first microporous bismuth silicates reported so far.