Molecular structure of arsabenzene: analysis combining electron diffraction and microwave data

The average ( r z structure of vapor-phase C 5 H 5 As, the arsenic congener of pyridine, was deduced. Vibrational corrections of diffraction data and rotational constants were made via a normal coordinate analysis. The heterocyclic molecule was found to have a rigorously planar, C 2v structure with geometric parameters very close to those inferred from an earlier analysis of the diffraction data alone, but uncertainties were reduced substantially by incorporation of the spectroscopic information in refinements. Amplitudes of vibration were determined from both the diffraction and normal coordinate analyses. Principal structural parameters and uncertainties (2.5σ) were r g (C-As) = 1.850(2) A, r g (C 2 -C 3 ) = 1.392(9) A, r g (C 3 -C 4 = 1.400(10) A, r g (C-C mean) = 1.396(2) A, ∠CAsC = 97.0(3)°, ∠AsCC = 125.3(7)°, and ∠C 3 C 3 = 123.9(13)°. Structural characteristics are those expected for an aromatic molecule.