Bridging Fluorine Research Articles

Reactions of tetrabutylammonium halides with boron trifluoride and phosphorus pentafluoride

Tetrabutylammonium halides react with one or more molecules of boron trifluoride or phosphorus pentafluoride at low temperature in dilute methylene chloride solution. Rapid, frequently concentration dependent equilibria occur in the nonideal solutions. The products isolated upon evaporation of solvent may not be those present in the dilute solutions. Usually a disproportionation occurs to yield BF4− or PF6−. With the exception of B2F7−, no complex ions involving fluorine bridging were found in solution or in the reaction products.

The crystal structure of gold trifluoride

Crystals of gold trifluoride are hexagonal, a= 5·149, c= 16·26 A, U= 373·3 A3, Dm= 6·72, Z= 6, Dc= 6·78, space-group P6122–D62. The structure was determined from a Patterson projection, and refined by three-dimensional least squares, the final R being 0·090 for 193 reflections.Gold trifluoride is a fluorine-bridged polymer, with gold atoms linked to square-planar arrangements of fluorine atoms. Each square-planar unit is linked to two adjacent units by cis fluorine bridges, giving an infinite hexagonal helix, with Au–F (bridging)= 2·04 A, Au–F (non-bridging)= 1·91 A, Au–F–Au = 116°. Weak cross-linking between chains, with Au⋯F = 2·69 A, completes a tetragonally-elongated octahedral environment around each gold atom.Gold trifluoride is the least densely packed of the noble-metal trifluorides. This and the geometry of the fluorine ligand co-ordination are consistent with the antibonding nature of one of the electron pairs of the low-spin d8 electron configuration of gold(III).

The crystal structure of germanium difluoride

Crystals of germanium difluoride are orthorhombic, a= 4·682, b= 5·178, c= 8·312 A, Z= 4, space group P212121. The structure was determined from the three-dimensional Patterson function, and refined by least-squares, the final R being 0·129 for 225 reflexions.The fluoride is a strong fluorine-bridged chain polymer, in which the parallel chains are cross-linked by weak fluorine bridges. The structural unit of the strongly bridged chains is a trigonal pyramid of three fluorine atoms and an apical germanium atom, with Ge–F distances of 1·79, 1·91, and 2·09 A and F–Ge–F angles of 85·0, 85·6, and 91·6°. The two longer-bonded fluorine atoms are structurally equivalent and join each germanium atom to its two neighbours in the chain. The fluorine atom 1·79 A distant from each germanium atom makes a weak bridge bond with a germanium atom in an adjacent chain, 2·57 A distant. This longest-bonded fluorine atom is almost opposite the fluorine atom at 2·09 A, the F–Ge–F angle being 163°. The poor fluorine atom packing and the geometry of the [GeF4] group are consistent with steric activity of the non-bonding valence electron pair. The [GeF4] group may be described as a distorted trigonal bipyramidal arrangement of four fluorine ligands and an (equatorial) electron pair, about a germanium atom.