SYNTHESIS AND STRUCTURE OF (H2O.HBF4)2(18-CROWN-6)

The title compound has been prepared by the addition of fluoroboric acid to 18-crown-6 in toluene. The compound crystallizes in the triclinic space group P1BAR with a = 7.341(2), b = 8.364(2), c = 10.631(3) angstrom, alpha = 71.48(2), beta = 67.91(2). gamma = 67.94(2)-degrees, and D(c) = 1.44 g cm-3 for Z = 1. The final conventional R value was 0.079 based on 1575 observed reflections. The molecule resides on a center of inversion. The (H2O.HBF4) moieties are best viewed as fluoroboric acid monohydrate molecules hydrogen bonded to the crown ether, one above and one below the plane of the crown. The F . . . O(water) hydrogen bond separation is 2.474(5) angstrom, and the 0(crown) . . . O(water) separations are 2.834(5) and 2.841(6) angstrom. The oxygen atoms of the crown ether are planar to 0.23 angstrom.