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

The first crystal and molecular structures of hydrated bis(n-perfluoroalkyl )phosphinic acids, [H3O](+) [(R-f)(2)PO2](-) (R-f=C6F13, C7F15 or C8F17), h ave been determined by single crystal X-ray diffraction. [H3O](+)[(C6F13)(2 )PO2](-) 1 and [H3O](+)[(C7F15)(2)PO2](-) 2 crystallize in the triclinic sp ace group (P (1) over bar) and [H3O](+)[(C8F17)(2)PO2](-). Me2CO 3 crystall izes in the orthorhombic space group Pca2(1). In each case the phosphorus a tom is tetrahedral and the perfluoroalkyl chains have a zigzag planar confo rmation. The structures consist of infinite sheets of the perfluoroalkyl ph osphinate held together by hydrogen bonding with the counter ion H3O+. In c ompound 3 the additional solvent molecule participates in extended donor-ac ceptor bonding and helps to expand the three dimensional structure. Some cl ose contacts between two atoms of two different molecules were also observe d.