Alkaline earth metal poly(hydrogen fluorides) hexafluoroarsenates(V) and hexafluorophosphate(V): M2(H2F3)(HF2)2(AF6) (M = Ca, A = As; M = Sr, A = As, P)

New compounds of the type M2(H2F3)(HF2)2(AF6) with M = Ca, A = As and M = Sr, A = As, P) were isolated. Ca2(H2F3)(HF2)2(AsF6) was prepared from Ca(AsF6)2 with repeated additions of neutral anhydrous hydrogen fluoride (aHF). It crystallizes in a space group P4322 with a = 714.67(10) pm, c = 1754.8(3) pm, V = 0.8963(2) nm3 and Z = 4. Sr2(H2F3)(HF2)2(AsF6) was prepared at room temperature by dissolving SrF2 in aHF acidified with AsF5 in mole ratio SrF2:AsF5 = 2:1. It crystallizes in a space group P4322 with a = 746.00(12) pm, c = 1805.1(5) pm, V = 1.0046(4) nm3 and Z = 4. Sr2(H2F3)(HF2)2(PF6) was prepared from Sr(XeF2)n(PF6)2 in neutral aHF. It crystallizes in a space group P4122 with a = 737.0(3) pm, c = 1793.7(14) pm, V = 0.9744(9) nm3 and Z = 4. The compounds M2(H2F3)(HF2)2(AF6) gradually lose HF at room temperature in a dynamic vacuum or during being powdered for recording IR spectra or X-ray powder ray diffraction patterns. All compounds are isotypical with coordination of nine fluorine atoms around a metal center forming a distorted Archimedian antiprism with one face capped. This is the first example of the compounds in which H2F3− and HF2− anions simultaneously bridge metal centers forming close packed three-dimensional network of polymeric compounds with low solubility in aHF. The HF2− anions are asymmetric with usual F⋯F distances of 227.3–228.5 pm. Vibrational frequency (ν1) of HF2− is close to that in NaHF2. The anion H2F3− exhibits unusually small F⋯F⋯F angle of 95.1°–97.6° most probably as a consequence of close packed structure.