One-pot occurrence of two polymorphs of Rb{sub 2}Sc[Si{sub 4}O{sub 10}]F and their structural, spectroscopic and computational characterization
- Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, A-6020 Innsbruck (Austria)
- Helmholtz-Zentrum Berlin für Materialien und Energie, Department of Crystallography, Hahn-Meitner-Platz 1, D-14109 Berlin (Germany)
Single-crystal growth experiments in the system RbF–Sc{sub 2}O{sub 3}–SiO{sub 2} resulted in the crystallization of two forms of Rb{sub 2}Sc[Si{sub 4}O{sub 10}]F within the same run. Basic crystallographic data of the two concomitant polymorphs at ambient conditions are as follows: phase I: space group I4/m, a=11.2619(3) Å, c=8.3053(4) Å, V=1053.36(6) Å{sup 3}, Z=4; phase II: space group P2{sub 1}/m, a=11.5085(6) Å, b=8.3805(3) Å, c=11.6750(6) Å, β=111.147(6)°, V=1050.19(9) Å{sup 3}, Z=4. The structures were determined by direct methods and refined to residuals of R(|F|)=0.0231 (phase I) for 516 and 0.0249 (phase II) for 2050 independent observed reflections with I>2σ(I). Phase I showed twinning by merohedry which was accounted for during the refinement process. Both compounds are based on multiple chains of [SiO{sub 4}]-tetrahedra forming closed columns or tubes. The multiplicity of the unbranched fundamental chains is two (for phase I) and four (for phase II), respectively. The periodicity of the multiple chains has a value of four in both modifications which is also reflected in similar translation periods along the chain directions (phase I: t{sub [001]}=8.31 Å; phase II: t{sub [010]}=8.38 Å). Alternatively, both polymorphs can be described as mixed octahedral–tetrahedral frameworks, which can be classified according to their polyhedral microensembles. A topological analysis of both networks is presented. Structural investigations have been supplemented by micro-Raman spectroscopy. The interpretation of the spectroscopic data including the allocation of the bands to certain vibrational species has been aided by DFT-calculations. - Graphical abstract: Mixed tetrahedral–octahedral framework of the tetragonal polymorph of Rb{sub 2}Sc[Si{sub 4}O{sub 10}]F. - Highlights: • We report the crystal structures of two polymorphs of Rb{sub 2}ScSi{sub 4}O{sub 10}F. • Both phases crystallized concomitantly in the same flux-growth experiment. • The mixed tetrahedral–octahedral nets are compared using a topological approach. • Interpretation of the Raman spectra has been aided by DFT-calculations.
- OSTI ID:
- 22451114
- Journal Information:
- Journal of Solid State Chemistry, Vol. 220; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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