Mixed-Anion [AsF6]−/[SbF6]− Salts of Cs+ and [XeF5]+; Incommensurately Modulated Crystal Structures of [XeF5][As1‑xSb x F6] (x ≈ 0.5 and 0.7)

Crystallizations of CsAsF6/CsSbF6 were carried out in anhydrous hydrogen fluoride (aHF) at various molar ratios. The compositions of the grown single crystals as refined from the X-ray diffraction data correspond to Cs­[As1‑x Sb x F6] (x = 0.13–0.87), which means that most probably all phases with x = 0–1 exist. They crystallize in the trigonal R 3̅ space group (no. 147). As5+ and Sb5+ are randomly distributed on the same crystallographic site. Crystal growth from aHF solutions of dissolved [XeF5]­[AsF6] and [XeF5]­[SbF6] mixtures in different initial ratios resulted in single crystals of [XeF5]­[As1‑x Sb x F6] (x ≈ 0.3 and 0.7) salts. The [XeF5]­[As0.5Sb0.5F6] crystallizes in two crystal modifications at low (α-phase, T < 180 K) and high (β-phase, T > 180 K) temperatures. α-[XeF5]­[As0.5Sb0.5F6] is orthorhombic with space group Pca21 (no. 29). Orthorhombic [XeF5]­[As0.3Sb0.7F6] (100–295 K) and β-[XeF5]­[As0.5Sb0.5F6] adopt a (3 + 1)-dimensionally incommensurately modulated crystal structure (superspace group Ama2­(00g)­s0s). Crystal data of [XeF5]­[As0.3Sb0.7F6]: a = 10.031(1) Å, b = 13.362(1) Å, c = 11.808(1) Å, V = 1582.9(5) Å3, modulation wavevector q = 0.6672c*, and Z = 8 at 200 K. Unit cell parameters of β-[XeF5]­[As0.5Sb0.5F6] at 295 K: a = 10.1196(5) Å, b = 13.4517(6) Å, c = 11.8999(5) Å, V = 1619.8(2)­Å3, modulation wavevector q = 0.6519c*, and Z = 8.