Single-crystal structures of A ₂SiF₆ (A = Tl, Rb, Cs), a better structure model for Tl₃[SiF₆]F, and its novel tetragonal polymorph

Abstract

We report on the syntheses and single-crystal structure determinations of the compounds A 2SiF6 (A = Tl, Rb, Cs). In comparison to the previous powder-based structure models we achieved more precise atom positions and distances. The compounds crystallize in the K2PtCl6 structure type, space group Fm 3 ‾ $‾{3}$ m (No. 225, cF36) with a = 8.4749(10) Å, V = 608.7(2) Å3, Z = 4 at T = 100 K for Tl2SiF6, a = 8.3918(10) Å, V = 591.0(2) Å3, Z = 4 at T = 100 K for Rb2SiF6, and a = 8.8638(11) Å, V = 696.4(3) Å3, Z = 4 at T = 200 K for Cs2SiF6. For the compound Tl3[SiF6]F we present a previously unknown tetragonal modification and correct the crystal structure of its trigonal modification to hexagonal. The tetragonal one crystallizes in the (NH4)3[SiF6]F structure type, space group P4/mbm (No. 127, tP22) with a = 8.0313(8), c = 5.8932(6) Å, V = 380.13(7) Å3, Z = 2, T = 298 K, and the crystal structure of the hexagonal modification is best described in space group P63 mc (No. 186, hP22) with a = 7.8248(4), c = 6.8768(4) Å, V = 364.64(4) Å3, Z = 2, T = 100 K.

Reactions of [SiF4(NH3)2] with Fluorides AF (A = Li–Cs, Tl, NH4) in Liquid NH3: A [NH4(NH3)2]+ Cation and a Thallophilic Interaction in [Tl2(NH3)6]2+

“…The F–Si–F angles within the anion are almost ideal with 89.95(11)°, 89.95(9)°, 90.05(9)°, and 90.05(11)°. These Si–F bond lengths agree with those of [NH 4 (NH 3 ) 2 ] 2 [SiF 6 ] [1.652(2)–1.692(2) Å], K 2 [SiF 6 ] [1.683(2)–1.706(9) Å], Rb 2 [SiF 6 ] [1.693(3) Å], Tl 2 [SiF 6 ] [1.686(6) Å], and Cs 2 [SiF 6 ] [1.679(4) Å], KLi­[SiF 6 ] [1.676(1)–1.701(1) Å], CsLi­[SiF 6 ] [1.667(2)–1.699(2) Å], and (NH 4 ) 2 [SiF 6 ] [1.688(3) Å] …”

Pb2(SeO3)(SiF6): the first selenite fluorosilicate with a wide bandgap and large birefringence achieved through perfluorinated group modification

“…Bond valence calculations indicate that the oxidation state of Se(1) is 3.958. The oxidation state of Si(1) is 4.513, which is relatively elevated and commonly observed in hexafluoro silicate compounds, such as compounds KLiSiF 6 (Si: 4.496), 48 Tl 2 SiF 6 (Si: 4.506) 49 and Li 2 SiF 6 (Si: 4.518). 50 Given that it is not an isolated case, we believe the high bond valence may be caused by the overestimated bond valence parameter (1.58) for the Si 4+ –F bond.…”

Luminescence and Formation of Cubic and Hexagonal (K,Rb)2SiF6:Mn4+

“…From top to bottom, the diffractograms of hexagonal KRbSiF 6 , cubic K 2 SiF 6 , cubic KRbSiF 6 , and cubic Rb 2 SiF 6 doped with 0.5% Mn 4+ are shown. Below the experimental patterns, the reference patterns are plotted. ,, Note that these diffractograms are recorded using a Co X-ray source.…”

“…Below the experimental patterns, the reference patterns are plotted. 9,21,22 Note that these diffractograms are recorded using a Co X-ray source. components allow for breaking the parity selection rule.…”