Crystal structures of isotypic ASb2F11 (A = Rb+, Tl+, O2+) and β-NH4Sb2F11, and the crystal structure of the low-temperature α-NH4Sb2F11

Abstract

The crystal structures of RbSb2F11, TlSb2F11, O2Sb2F11 and β-NH4Sb2F11 salts are isotypical and crystallize in the orthorhombic space group Cmc21 (No. 36). Crystal data of rubidium salt: a = 19.9981(3) Å, b = 11.5093(2) Å, c = 12.9623(2) Å, V = 2983.46(8) Å3, and Z = 12 at 150 K. Unit cell parameters of corresponding thallium salt: a = 19.9876(5) Å, b = 11.5400(3) Å, c = 13.0267(3) Å, V = 3004.70(13) Å3 and Z = 12 at 150 K. Reaction between NH4F and excess of SbF5 in anhydrous HF resulted in the single-crystal growth of β-NH4Sb2F11: a = 20.0406(7) Å, b = 11.5534(4) Å, c = 13.0796(4) Å, V = 3028.42(18) Å3, and Z = 12 at 296 K. The XRD experiments on NH4Sb2F11 at 240 and 150 K revealed another modification (α-NH4Sb2F11), which crystallizes in a (pseudo-hexagonal) monoclinic cell, space group P21, a = 11.5045(6) Å, b = 13.0437(3) Å, c = 11.5264(6) Å, β = 119.818(7)°, V = 1500.67(15) Å3, and Z = 6 at 240 K. Reaction between the O2SbF6 and SbF5 in anhydrous HF yielded O2Sb2F11 upon crystallization with a = 19.8472(5) Å, b = 11.1172(3) Å, c = 12.8259(3) Å, V = 2829.97(12) Å3, and Z = 12 at 150 K. The crystal structures of ASb2F11 (A = Rb+, Tl+, O2+, NH4+) salts consist of dimeric Sb2F11− anions with partially disordered terminal fluorine atoms. Negative charge of the anions is compensated by single charged cations. Crystal structure of α-NH4Sb2F11 demonstrates similar motif as in β-phase but with slightly re-arranged N―H… F hydrogen bonds. In the 100−296 K range, only rhombohedral phase was observed for NH4SbF6 (rhombohedral space group R3¯, No. 148) with a = b = 7.5961(9) Å, c = 7.7176(9) Å, α = β = 90°, γ = 120°, V = 385.65(12) Å3, and Z = 3 at 150 K).