CRYSTAL AND MOLECULAR STRUCTURES OF METHOXYTETRAPHENYLANTIMONY AND DIMETHOXYTRIPHENYLANTIMONY

The structures of methoxytetraphenylantimony, (C6H5)4SbOCH3, and dimethoxytriphenylantimony, (C6H5)3Sb(OCH3)2, have been determined from three-dimensional single crystal X-ray diffraction counter data. Both compounds are monomeric and contain pentacoordinated antimony atoms. Methoxytetraphenylantimony crystallizes with eight molecules in space group Pbca of the orthorhombic system with cell dimensions of a = 14.81 (2), b = 16.95 (3), c = 16.74 (2) Å V = 4202 Å3. The conformation of the organic ligands around the antimony atom is that of a trigonal bipyramid with the methoxyl group occupying one of the apical positions. The Sb-O bond distance is 2.061 (7) Å. The apical Sb-C bond distance of 2.199 (14) A is significantly longer than the equatorial Sb-C distances of 2.131 (11), 2.128 (13), and 2.097 (15) Å. The Sb atom is displaced 0.10 Å out of the equatorial plane toward the apical phenyl group. Dimethoxytriphenylantimony crystallizes with four molecules in space group P21/c of the monoclinic system with cell dimensions of a = 11.51 (2), b = 9.40 (2), c = 17.30 (3) Å; β = 101.75 (1)°; V = 1832 Å3. The trigonal bipyramidal conformation around the antimony atom has a carbon atom from each of the three benzene rings in the equatorial plane with Sb-C distances of 2.119 (10), 2.121 (11), and 2.119 (12) Å. The methoxyl groups occupy both apical positions with Sb-O bond distances of 2.039 (8) and 2.027 (8) Å. The conventional crystallographic R factors are respectively 2.8 and 3.4%. The nmr spectrum of methoxytetra-p-tolylantimony has been taken and a single sharp peak was observed for the p-methyl protons. This result suggests that this compound exists in solution either as a rapidly established equilibrium mixture of trigonal-bipyramidal and square-pyramidal configurations or as the latter configuration only. © 1968, American Chemical Society. All rights reserved.