The molecular structure of gaseous trimethylarsenic difluoride as determined by electron diffraction

Abstract

The structure of gaseous trimethylarsenic difluoride has been determined by electron diffraction using a heated inlet system. The results are consistent with the presence of a single species, the monomer (CH₃)₃AsF₂ with freely rotating CH₃ groups occupying the equatorial sites of a framework in the form of a trigonal bipyramid to complete a heavy-atom skeleton with D_3h symmetry. Salient structural parameters (r_a) are: r(As–F) 182.0(0.6), r(As–C) 189.7(0.6), and r(C–H) 110.7(1.3); As–C–H 107.9(1.5)°. Comparisons with the structures of related molecules show that the switch from AsF₅ to (CH₃)₃AsF₂, like that from PF₅ to (CH₃)₃PF₂, results in the retention of the axial F–E–F unit (E = P or As), but with a significant attenuation of the E–F bond.