title: The OC(2)F(5)(-), OCF(CF(3))(2)(-), and OCFCF(2)O(-) Anions: Preparation and Structure.
abstract: The compounds pip(+)CF(3)O(-), pip(+)CF(3)CF(2)O(-), pip(+)(CF(3))(2)CFO(-), and (CH(3))(4)N(+)OCFCF(2)O(-) (pip(+) = 1,1,3,3,5,5-hexamethylpiperidinium) are obtained from pip(+)F(-) or (CH(3))(4)N(+)F(-) and COF(2), CF(3)COF, (CF(3))(2)CO, and (COF)(2). The structures of pip(+)CF(3)CF(2)O(-), pip(+)(CF(3))(2)CFO(-), and (CH(3))(4)N(+)OCFCF(2)O(-) have been investigated by single-crystal X-ray crystallography. Crystal data are as follows: for pip(+)CF(3)CF(2)O(-), monoclinic P2(1)/c, a = 1300.7(1) pm, b = 828.0(1) pm, c = 1513.3(2) pm, beta = 110.13(1) degrees, Z = 4; for pip(+)(CF(3))(2)CFO(-), monoclinic P2(1)/c, a = 1182.2(1) pm, b = 1032.9(2) pm, c = 1459.1(1) pm, beta = 107.45(1) degrees, Z = 4; for (CH(3))(4)N(+)OCFCF(2)O(-), tetragonal P&fourmacr;2(1)/c, a = 1115.9(1) pm, c = 1377.1(1) pm, Z = 8. All anion structures are indicative of a negative hyperconjugation effect. The structure of FCOCF(2)O(-) is clearly nonsymmetric and resembles a close to planar cis oxygen configuration with one additional fluorine bound to one carbon atom. This fluorine atom is positioned slightly toward the second carbon atom, which corresponds to a movement from the asymmetric to the symmetric fluorine-bridged structure. Interionic forces seem to be responsible for this peculiar structure. These findings are compared with structures predicted by ab initio calculations.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Freie Universität, 14195 Berlin, Germany.
authors.forename: X.
authors.initials: X
authors.lastname: Zhang
authors.forename: K.
authors.initials: K
authors.lastname: Seppelt