Crystal structures of diphenylantimony(V) tribromide, dibromide chloride, and bromide dichloride

The crystal structures of SbBr3Ph2(1), SbBr2Ph2Cl (2), and SbBrPh2Cl2(3) have been determined by Patterson and Fourier methods from X-ray diffractometer data and refined by least squares to R 0.080 (1)(997 reflections), 0.046 (2)(917), and 0.058 (3)(979) respectively. Crystals of all the compounds are orthorhombic, space group Cmc21, Z= 4, with unit-cell dimensions: (1)a= 15.49(1), b= 10.96(1), c= 8.07(1): (2)a= 15.44(1), b= 10.97(1), c= 7.93(1); (3)a= 15.25(1), b= 11.00(1), c= 7.83(1)Å. In all cases the heavy atoms lie on a mirror plane and the structure contains antimony in distorted trigonal-bipyramidal co-ordination, with a bromine atom and two phenyl groups (related by the mirror plane) in the equatorial positions. Antimony–bromine equatorial distances decrease from 2.478(3) to 2.446(4)Å with increasing chlorine content; the Sb–C distances show a similar but smaller variation and are close to 2.14 Å. The two bonds from antimony to the axial halogen atoms have different lengths in all three compounds, with the halogen at the greater distance being involved in weak intermolecular bonding to a neighbouring antimony atom. The intermolecular bonds vary between 3.433(3) and 3.363(5)Å. Problems arise in the case of (2) since there is disorder in the bromine–chlorine occupancy of the two axial positions. A major consequence of the intermolecular interaction is an increase in the C–Sb–C angle from the expected value of 120 to ca. 154°.