Two synthetic gallosilicates and a gallogermanate with the NAT, EDI and THO framework topologies have been synthesized under hydrothermal conditions and characterized by single crystal synchrotron X-ray diffraction. K-GaSi-NAT, K8Ga8Si12O40 · 6H2O, is tetragonal, space group I42d, with a = 13.639(2), c = 6.545(1) Å. The framework model shows complete disordering of Ga and Si in tetrahedral sites, which is analogous to tetranatrolite but contrasts with the partial ordering in Na-GaSi-NAT. The T-sites of RbNa-GaSi-EDI, Rb7NaGa8Si12O40 · 3H2O, exhibit partial disordering of Ga and Si in space group P421c. This leads to a cell doubling along the chain axis (c) with a = 9.773(1), c = 13.141(3) Å, a super cell modification of the Na-exchanged K-F structure. In Rb-GaGe-THO, Rb20Ga20Ge20O80 · 15H2O, a = 14.335(3), b = 14.198(3), c = 13.421(3) Å, complete ordering on both tetrahedral and extra-framework sites lowers the symmetry from Pncn to the acentric space group Pn2n. An inspection of framework T-O-T bond angles, which are related to rotation and distortion of the chains, explains the differences in unit cells between these gallium- and germanium-variants and aluminosilicate analogs. The elliptical 8-ring windows, generated by four crosslinked chains in RbNa-GaSi-EDI and Rb-GaGe-THO, are the sites for (Rb, Na) and Rb cations, respectively, while the helical 8-ring channels formed in K-GaSi-NAT host only water molecules. The T10O20 windows, built by two neighboring chains, provide sites for K or Rb cations in each model. Mechanisms are proposed for cation-framework interactions, which are in turn responsible for the observed framework models. (C) 2000 Elsevier Science B.V. All rights reserved.
Bibliographical noteFunding Information:
The authors thank the NSF (Grant DMR 97-13375) for financial support. Research carried out in part at the National Synchrotron Light Source at Brookhaven National Laboratory is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences. The SUNY X3A beamline of the NSLS is supported by the Division of Basic Energy Sciences of the U.S. Department of Energy (DE-FG02-86ER45231). Special thanks to Guang Wu of the SUNY X3A beamline and Jonathan C. Hanson of beamline X7B of the NSLS. Robert Rapp is acknowledged for chemical analysis, and SJK is grateful for the partial support from Korea Institute of Science and Technology (KIST) and Korea Science and Engineering Foundation (KOSEF).
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials