XeOF_5~-, an Anion with Pentagonal-Pyramidal Structure

摘要

XeOF_4 and IF_5 have strikingly similar physical, chemical, and structural properties. Both have a square-pyramidal structure and show distinct intermolecular interactions in condensed phase. With fluoride acceptors they form the cations IF_4 and XcOF_3~-. which have a similar structure. Alkali metal fluorides dissolve in IF, and XeOF_4 to form the crystalline associates F ~- centre dot 3 IF, and F centre dot 3 XeOF_4. which also display almost identical structures in which the three square-pyramidalIF, and XeOF_4 units solvate the F ion, but themselves remain structu-ally virtually unaltered. Removal of IF_5 or XeOF_4 from these associates in vacuum yields the anions IF_6~- and XeOF_5~- . Because the salts always form as powders, structural investigations were difficult. (CH_3)_4N~+IF_6~- could, however, be obtained in the form of single crystals. The structure of the anion IF_6~- is an octahedron strongly distorted towards C_(3v) symmetry. Because of its steric effect the nonbonding lone electron pair lies on the threefold axis. With the small cation NO~+ as counterion an I_4F_(24)~(4-) cluster is obtained, which resembles the tetramer found in solid XeF6 and its solutions.