A synthetic alummogermanate and a gallogermanate with the Cancrinite group (CAN) framework topology have been synthesized under hydrothermal conditions and characterized by single crystal synchrotron X-ray diffraction. AlGe-CAN, Na6Cs2Al6Ge6O24·Ge(OH)6, is hexagonal, with the space group P63 and a = 12.968(1), c = 5.132(1) angstroms, V = 747.4(1) angstroms3. The T-sites exhibit complete ordering of Al and Ge atoms, similar to the framework models of aluminosilicate analogues. GaGe-CAN, Na6Cs2Ga6Ge6O24·Ge(OH)6, is hexagonal, apparently with the space group P63mc and a = 12.950(2), c = 5.117(1) angstroms, V = 743.2(2) angstroms3. Although the observed data are consistent with the presence of the c-glide and consequent disordering of Ga and Ge atoms at the T-sites, calculation using a DLS-optimized framework in the space group P63 reveals that the intensities of the hh2̄h̄l reflections with l = 2n+1 are less than 0.07% of the strongest (0 0 0 2) reflection, suggesting that P63 is probably the true space group. Resonant diffraction studies performed in the vicinity of the Ga K-edge confirmed the presence of the hh2̄h̄l reflections with l = 2n+1 and thus confirmed the ordering of the framework Ga/Ge atoms in GaGe-CAN. Inspection of the framework T-O-T bond angles demonstrates greater relative cell contraction for GaGe-CAN compared to AlGe-CAN and aluminosilicate counterparts. In both the structural models, Ge(OH)6 octahedra are occluded in the 12-ring channels running along the 63-axes. The sodium cations fully occupy the sites above the 6-ring windows in the 12-ring channels. The cesium cations fully occupy the sites in the middle of the cancrinite cages. Subtle differences in the coordination geometries of the extra-framework species are found, perhaps due to the pseudo-symmetry of GaGe-CAN. Thermogravimetry results indicate net weight losses of 3.5% and 3.0% for AlGe-CAN and GaGe-CAN, respectively, which are explainable by the dehydration of the Ge(OH)6 octahedra. In situ synchrotron X-ray powder diffraction demonstrated the formation of GaGe analogue of the nepheline hydrate I type structure at the temperature of complete dehydration.
Bibliographical noteFunding Information:
The authors thank the NSF for financial support (Grant DMR 97-13375). Research carried out in part at the NSLS at BNL is supported by the US Department of Energy, Division of Materials Sciences and Division of Chemical Sciences, Office of Basic Energy Sciences (Grant DE-FG02-86ER45231 for the SUNY X3A beamline, Grant DE-Ac02-98CH10886 for the X7A beamline and Grant DE-AC02-98CH10886 for the X7B beamline). Special thanks to Guang Wu of the SUNY X3A beamline and Jonathan C. Hanson of the X7B beamline of the NSLS for their help with the data collections. 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