The first crystal and molecular structures of hydrated bis(n-perfluoroalkyl)phosphinic acids [H3O]+[(Rf)2PO2]− (Rf = C6F13, C7F15 or C8F17)

Abstract

The first crystal and molecular structures of hydrated bis(n-perfluoroalkyl)phosphinic acids, [H₃O]⁺ [(R_f)₂PO₂]⁻ (R_f = C₆F₁₃, C₇F₁₅ or C₈F₁₇), have been determined by single crystal X-ray diffraction. [H₃O]⁺[(C₆F₁₃)₂PO₂]⁻1 and [H₃O]⁺[(C₇F₁₅)₂PO₂]⁻2 crystallize in the triclinic space group (P) and [H₃O]⁺[(C₈F₁₇)₂PO₂]⁻·Me₂CO 3 crystallizes in the orthorhombic space group Pca2(1). In each case the phosphorus atom is tetrahedral and the perfluoroalkyl chains have a zigzag planar conformation. The structures consist of infinite sheets of the perfluoroalkyl phosphinate held together by hydrogen bonding with the counter ion H₃O⁺. In compound 3 the additional solvent molecule participates in extended donor–acceptor bonding and helps to expand the three dimensional structure. Some close contacts between two atoms of two different molecules were also observed.