Motaln K, Lozinšek M. Crystal structure of CaSiF
6·2H
2O(
mP2) and reevaluation of the Si
IV-F bond-valence parameter
R0.
Acta Crystallogr E Crystallogr Commun 2023;
79:1121-1126. [PMID:
38313128 PMCID:
PMC10833414 DOI:
10.1107/s2056989023009349]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Accepted: 10/25/2023] [Indexed: 02/06/2024]
Abstract
The structure of a second polymorph of CaSiF6·2H2O [calcium hexafluorido-silicate dihydrate; space group P2/c (No. 13), Pearson symbol mP2] was elucidated by single-crystal X-ray diffraction. It arose as an unexpected product when soda-lime glass was attacked by HF. Its crystal structure consists of infinite ∞ 2[Ca(H2O)2/1(SiF6)4/4] layers oriented parallel to the bc-crystallographic plane, a unique motif among structurally characterized hydrated hexa-fluorido-silicates. The crystal structure also exhibits inter- and intra-layer hydrogen bonds, with the inter-layer O-H⋯O hydrogen bonds involving a disordered hydrogen atom. The large deviation between the calculated bond-valence sum for Si and the expected value prompted a redetermination of the empirical SiIV-F bond-valence parameter R 0. Based on a data set of 42 high-quality crystal structures containing 49 independent SiIV coordination environments, a revised value of 1.534 Å was derived for R 0.
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