In:
Zeitschrift für Kristallographie - Crystalline Materials, Walter de Gruyter GmbH, Vol. 235, No. 8-9 ( 2020-09-25), p. 247-254
Abstract:
Herein we present the synthesis, crystal structure, and the infrared and Raman spectra of K 3 Na 4 [SiF 6 ] 3 [BF 4 ]. The compound also occurs in nature as the mineral Knasibfite. We obtained it from the reaction of stoichiometric amounts of SiO 2 , Na[BF 4 ], K 2 CO 3 , and Na 2 CO 3 in hydrofluoric acid at room temperature. Hydrofluorothermal synthesis at 200 °C lead to a product of higher purity. Knasibfite is colorless and crystallizes in space group Im 2 m with a = 5.546(2), b = 9.261(2), c = 17.184(4) Å, V = 882.5(4) Å 3 , Z = 2, at T = 400(2) K. At 342 K a phase transition to a monoclinic structure was observed ( I 2, a = 5.5003(6), b = 9.0890(9), c = 17.0048(2) Å, β = 90.041(9)°, V = 852.2(2) Å 3 , Z = 2, T = 100(2) K). By replacing SiO 2 with GeO 2 as a starting material K 3 Na 4 [GeF 6 ] 3 [BF 4 ] was obtained. This compound also crystallizes in form of two polymorphs, both of which are isotypic to the respective ones of K 3 Na 4 [SiF 6 ] 3 [BF 4 ].
Type of Medium:
Online Resource
ISSN:
2196-7105
,
2194-4946
DOI:
10.1515/zkri-2019-0068
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
2020
SSG:
13
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