Franconite, NaNb2O5(OH)·3H2O: structure determination and the role of H bonding, with comments on the crystal chemistry of franconite-related minerals
| Autor: | Monika M. M. Haring, Andrew M. McDonald |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
Hydrogen bond
Crystal chemistry Chemistry Cleavage (crystal) 02 engineering and technology Crystal structure 010502 geochemistry & geophysics 021001 nanoscience & nanotechnology Molecular sieve 01 natural sciences Crystallography Octahedron Geochemistry and Petrology Group (periodic table) 0210 nano-technology Powder diffraction 0105 earth and related environmental sciences |
| Zdroj: | Mineralogical Magazine. 78:591-607 |
| ISSN: | 1471-8022 0026-461X |
| Popis: | The crystal structure of franconite, NaNb2O5(OH)·3H2O, has been characterized by single-crystal X-ray diffraction using material from Mont Saint-Hilaire, Québec, Canada. Results givea= 10.119(2),b= 6.436(1),c= 12.682(2) Å and β = 99.91(3)° and confirm the correct space group asP21/c. The crystal structure, refined toR= 4.63% andwR2=11.95%, contains oneNasite, two distorted octahedralNbsites and nineOsites. It consists of clusters of four edge-sharing Nb(O,OH)6octahedra, linked through shared corners to adjacent clusters, forming layers of Nb(O,OH)6octahedra. These alternate along [100] with layers composed of NaO(H2O)4polyhedra, the two being linked together by well defined H bonding. The predominance of H bonding, essential to the mineral, results in a perfect {100} cleavage. Chemical analyses (n= 7) of four crystals give the empirical formula (Na0.73Ca0.13☐0.14)∑=1.00(Nb1.96Ti0.02Si0.02Al0.01)∑=2.01O5(OH)·3H2O (based on nine oxygens) or ideally NaNb2O5(OH)·3H2O. Franconite is crystallo-chemically related to SOMS [Sandia Octahedral Molecular Sieves; Na2Nb2−xMxO6−x(OH)x·H2O with M = Ti, Zr, Hf], a group of synthetic compounds with strong ion-exchange capabilities. Both hochelagaite (CaNb4O11·nH2O) and ternovite (MgNb4O11·nH2O) have X-ray powder diffraction patterns and cation ratios similar to those of franconite indicating that these minerals probably have similar structures. |
| Databáze: | OpenAIRE |
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