Crystal structure of a new small-pore zirconosilicate Na_2ZrSi_2O_7 centre dot H_2O and its relation to stoichiometrically and topologically similar compounds

摘要

The small-pore zirconosilicate Na_2ZrSi_2O_7 centre dot H_2O crystallizes in monoclinic system with space group C2/c, a = 5.4715(4); b = 9.4111(6); c = 13.0969(8) A, beta = 92.851(7) deg. Its framework consists of layers built of ZrO_6 octahedra and SiO_4 tetrahedra and forming condensed [Si_2O_7] pyrogroups by connection. The sodium ions and water molecules are placed in channels set up between the layers. The stoichiometric and structural similarities of the studied phase with anhydrous compounds having general chemical formula A_(2(3))MT_2O_7 (A = Na, K; M = Zr,Lu,Sc; T = Si,Ge) are discussed. The topological relationship of their structures is interpreted in the light of spatial combination of silicon and zirconium polyhedra as basic building units into larger composite building units and their three-dimensional arrangement.