Abstract Herein we present the synthesis, crystal structure, and the infrared and Raman spectra of K3Na4[SiF6]3[BF4]. The compound also occurs in nature as the mineral Knasibfite. We obtained it from the reaction of stoichiometric amounts of SiO2, Na[BF4], K2CO3, and Na2CO3 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 2m with a = 5.546(2), b = 9.261(2), c = 17.184(4) Å, V = 882.5(4) Å3, 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) Å3, Z = 2, T = 100(2) K). By replacing SiO2 with GeO2 as a starting material K3Na4[GeF6]3[BF4] was obtained. This compound also crystallizes in form of two polymorphs, both of which are isotypic to the respective ones of K3Na4[SiF6]3[BF4].

中文翻译：

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Knasibfite K3Na4[SiF6]3[BF4]和同源Ge化合物K3Na4[GeF6]3[BF4]的实验室合成和表征

摘要 本文介绍了 K3Na4[SiF6]3[BF4] 的合成、晶体结构以及红外和拉曼光谱。该化合物在自然界中也以矿物 Knasibfite 的形式存在。我们通过化学计量的 SiO2、Na[BF4]、K2CO3 和 Na2CO3 在室温下在氢氟酸中的反应获得它。在 200 °C 下氢氟热合成产生更高纯度的产品。Knasibfite 是无色的，在空间群 Im 2m 中结晶，a = 5.546(2), b = 9.261(2), c = 17.184(4) Å, V = 882.5(4) Å3, Z = 2, 在 T = 400( 2) K。在 342 K 观察到单斜结构的相变 (I 2, a = 5.5003(6), b = 9.0890(9), c = 17.0048(2) Å, β = 90.041(9)°, V = 852.2(2) Å3，Z = 2，T = 100(2) K)。通过用GeO2代替SiO2作为起始原料，得到了K3Na4[GeF6]3[BF4]。