Fluoride und Fluorosäuren. IV. Kristallstrukturen von Bortrifluorid und seinen 1:1-Verbindungen mit Wasser und Methanol,Hydroxo- und Methoxotrifluoroborsäure

Fluorides and Fluoro Acids. IV. Crystal Structures of Boron Trifluoride and its 1:1 Compounds with Water and Methanol, Hydroxo- and Methoxotrifluoroboric Acid Solid boron trifluoride displays an enantiotropic phase transition α ? β at ?147°C. A further solid phase, γ-BF₃, is metastable or stable only just below the melting point. Its crystal structure was determined. It is monoclinic with space group P2₁/c, eight molecules in the unit cell and the lattice parameters a = 4.779, b = 14.00, c = 7.430 Å, β = 107.60° at ?131°C. Two independent trigonal planar molecules with a mean B? F bond length of 1.287 Å (1.319 Å after correction for thermal motion) form a three-dimensional packing connection with non-parallel molecular planes across intermolecular B···F contacts of in the average 2.690 Å, by which the boron atoms achieve a total coordination of five fluorine atoms with nearly trigonal bipyramidal geometry. — The crystal structures of hydroxotrifluoroboric acid (BF₃OH₂, monoclinic, P2₁/n, Z = 4, a = 7.641, b = 7.957, c = 4.864 Å, β = 94.80 at ?35°C) and methoxotrifluoroboric acid (BF₃O(CH₃)H, orthorhombic, Pbca, Z = 8, a = 7.054, b = 9.390, c = 11.547 Å at ?40°C) display unlimited three-dimensional and one-dimensional linking, respectively, of the molecules by hydrogen bonds O? H···F.