Crystal and molecular structure of 1,1,2,2-tetrakis-(2-methoxyphenyl)-ethane. Phenyl group conformations in XPhn compounds

Abstract

The title compound has been shown (by a single-crystal X-ray analysis) to be one of the products from the thermal decomposition of solvated tris-(2-methoxyphenyl)chromium(III) in dioxan solution. The molecule has the symmetry and lies on a special position in the space group P2₁/c with a= 7·721(5), b= 8·929(6), c= 18·025(12)Å, β= 97·6(2)°. The structure was solved by direct methods. Least-squares refinement of 1326 diffractometer data gave a final R of 0·057. The central C–C bond length is 1·555(7)Å and a trigonal distortion at the sp³ carbon atom gives large C–C–C angles, near 111·5°. The carbon atoms of the methoxy-groups lie 0·24 and 0·16 Å from their corresponding benzenoid rings, and one of these rings is nearly parallel to the C(sp³)–H bond. Rotation of the methoxyphenyl groups by 7·5° about the C(sp²)–C(sp³) bonds would give the molecule a close approximation to the symmetry 2/m. Formulae are given, for molecules of the type XPh_n with a rotation or inversion symmetry axis, to calculate the ortho ⋯ ortho inter-ring distances as a function of the orientation of the rings about the X–C bond.