Potassium beryllium sulfate dihydrate, K2Be(SO4) 2 2H2O: Crystal structure and infrared spectroscopy
- Author(s)
- Mitko Georgiev, Manfred Wildner, Donka Stoilova, V Karadjova
- Abstract
The crystal and molecular structure of the title compound, K 2Be(SO4)2ž2H2O, as determined by single crystal X-ray diffraction and infrared spectroscopy is reported and discussed. K2Be(SO4)2ž2H2O crystallizes in the monoclinic space group P21/c (a.143(2), b.515(2), c=7.314(1) A°, ß•.08(1)°, V“4.8 A°3, Z=4, R1=0.034 for 3524 Fo>4s(F o) and 153 variables). The structure is characterized by tetrahedral chain fragments consisting of a BeO2(H2O)2 group sharing corners with two SO4 tetrahedra. These [Be(SO 4)2(H2O)2]2- units are interlinked by irregular KO7 polyhedra and hydrogen bonds. Generally, the observed bond lengths and angles comply well with crystal chemical experience. Most of the infrared and Raman bands corresponding to the internal vibrations of the SO42- ions appear as doublets, thus reflecting the existence of two crystallographically different [SO 4]-tetrahedra in agreement with the structural data. The strengths of the hydrogen bonds as deduced from the infrared wavenumbers of the uncoupled OD modes of matrix-isolated HDO molecules (bands at 2278, 2352 and 2388 cm -1, liquid nitrogen temperature) are discussed in terms of the the Ow?O bond distances, the different hydrogen bond acceptor capabilities of the oxygen atoms and the Be-OH2 interactions. The intramolecular OH bond lengths are derived from the ?OD vs. r OH correlation curve [J. Mol Struct. 404 (1997) 63]. The water librations couple intensively with the translatory modes of the Be2+ ions (BeO4 skeleton vibrations) and the normal modes of SO 42- ions, thus producing small isotopic shifts. The SO42- guest ions matrix-isolated in the isostructural host lattice K2Be(SeO4)2ž2H2O exhibit doublet bands in the region of the stretching modes (the bands corresponding to the bending modes could not be recognized well), thus indicating a statistical distribution of the guest ions over the two available crystallographic positions. The distortion of the SO42- guest ions in the host selenate lattice is weaker than that of the same ions in the neat sulfate owing to the larger unit-cell volume of the host compound, i.e. to the smaller repulsion potential of the host lattice. Œ 2005 Elsevier B.V. All rights reserved.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Technical University of Sofia, Bulgarian Academy of Sciences (BAS)
- Journal
- Journal of Molecular Structure
- Volume
- 753
- Pages
- 104-112
- No. of pages
- 9
- ISSN
- 0022-2860
- Publication date
- 2005
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography, 1030 Physics, Astronomy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/2ee33934-ee91-4c24-ab74-463ac966a7c2