The crystal structure of pentaphenylarsenic: implications for the role of crystal packing forces in the structures of penta-aryl Group V molecules

Abstract

The structure of the cyclohexane solvate of pentaphenylarsenic has been determined by X-ray crystallographic analysis. The substance crystallizes in space group P1, cell dimensions a= 10.448 (19), b= 10.566 (21), c-14.903 (25) A,, ~= 121.09 (5), fl= 106.38 (4), y= 92-44 (5) °, with one (C6Hs)sAs and onehalf C6H12 molecule in the asymmetric unit. The structural model, in which the phenyl rings were treated as rigid bodies, refined to a conventional R of 0.072 with 843 data collected on a Pailred Weissenberg-geometry diffractometer. The pentaphenylarsenic molecule is an undistorted trigonal bipyramid with average axial and equatorial As-C bond lengths of 2.105 (7) and 1.964 (11) A,, respectively. In spite of the different intermolecular interactions involved, the molecular conformation, as measured by phenyl ring rotations, of (C6Hs)sAs is very similar to that of the analogous phosphorus compound and to that of the antimony molecule in the cyclohexane solvate. Comparisons of this preferred conformation with the distorted trigonal-bipyramidal structure found for penta-p-tolylantimony and with the squarepyramidal geometry observed for unsolvated pentaphenylantimony illustrate the types of distortions which can result from solid-state packing interactions.