LAUSR

Abstract The improved synthesis of the homoleptic perchlorophenyl stibine (C 6 Cl 5 ) 3 Sb ( 1a ) has enabled us to obtain detailed spectroscopic and structural information. In contrast to the planar structure shown by the nitrogen homologue (C 6 Cl 5 ) 3 N, the antimony compound 1a shows unmistakable pyramidal structure (C–Sb–C 100.9(2)°, av.) with slightly elongated Sb–C bonds (219.6(4) pm, av.) with respect to the non-chlorinated model compound Ph 3 Sb. The Sb–C bonds shorten upon oxidation, as it is found in the oxidized compound (C 6 Cl 5 ) 3 SbCl 2 ( 2a ). A single isomer is stereoselectively obtained for this hypervalent compound 2a , namely that with the Cl ligands in axial positions. This neutral, hypervalent compound ( 2a ) is found to dissociate chloride in the gas phase (MS) giving rise to the [(C 6 Cl 5 ) 3 SbCl] + cation ( 3a ). According to theoretical calculations this cation should have nearly tetrahedral structure and behave as a Lewis superacid. The structural properties and Lewis acidity of compounds 1a – 3a are compared with those calculated for their corresponding isoelectronic tin derivatives ( 1b – 3b ).