Stereochemistry of some organic derivatives of Group Vb elements. Part IV. Crystal and molecular structure of 1-acetyl-2,3,4-triphenyl-5-(triphenylarsonio)cyclopentadienide

Abstract

The crystal structure of the title compound has been determined from three-dimensional X-ray data. Crystals are orthorhombic. space group Pbca, with Z= 8 in a unit cell of dimensions: a= 15·353(2), b= 24·377(3), c= 17·361(2)Å. The structure has been refined by block-diagonal least-squares methods to R 0·042 for 2977 observed reflexions. Molecular dimensions establish that a dipolar form [As⋯Ō 2·770(3)Å] makes a significant contribution to the ground-state structure and results in distorted trigonal bipyramidal geometry about arsenic. Principal mean dimensions are: As–C(eq Ph) 1·923(5), As–C(ax Ph) 1·925(5), and As–C(C₅H₅) 1·881(4)Å. The contributions of three canonical forms to the ground-state structure are assessed.