TETRACHLOROSTIBONIUM(V) AND TETRABROMOSTIBONIUM(V) CATIONS - RAMAN AND F-19, SB-121, AND SB-123 NMR SPECTROSCOPIC CHARACTERIZATION AND X-RAY CRYSTAL-STRUCTURES OF SBCL4-) AND SBBR4+SB(OTEF5)(6)(-)(SB(OTEF5)(6)()

The stable salts, SbCl4+Sb(OTeF5)(6)(-) and SbBr4+Sb(OTeF5)(6)(-), hav e been prepared by oxidation of Sb(OTeF5)(3) with Cl-2 and Br-2, respe ctively. The SbBr4+ cation is reported for the first time and is only the second example of a tetrahalostibonium(V) cation. The SbCl4+ catio n had been previously characterized as the Sb2F11-, Sb2Cl2F9-, and Sb2 Cl0.5F10.5- salts. Both Sb(OTeF5)(6)(-) salts have been characterized in the solid state by low-temperature Raman spectroscopy and X-ray cry stallography. Owing to the weakly coordinating nature of the Sb(OTeF5) (6)(-) anion, both salts are readily soluble in SO2ClF and have been c haracterized in solution by Sb-121, Sb-123, and F-19 NMR spectroscopy. The tetrahedral environments around the Sb atoms of the cations resul t in low electric field gradients at the quadrupolar Sb-121 and Sb-123 nuclei and correspondingly long relaxation times, allowing the first solution NMR characterization of a tetrahalocation of the heavy pnicog ens. The following crystal structures are reported: SbCl4+Sb(OTeF5)(6) (-), trigonal system, space group P (3) over bar, a = 10.022(1) Angstr om, c = 18.995(4) Angstrom, V = 1652.3(6) Angstrom(3), D-calc = 3.652 g cm(-3), Z = 2, R(1) = 0.0461; SbBr4+Sb(OTeF5)(6)(-), trigonal system , space group P (3) over bar, a = 10.206(1) Angstrom, c = 19.297(3) An gstrom, V = 1740.9(5) Angstrom(3), D-calc = 3.806 g cm(-3), Z = 2, R(1 ) = 0.0425. The crystal structures of both Sb(OTeF5)(6)(-) salts are s imilar and reveal considerably weaker interactions between anion and c ation than in previously known SbCl4+ salts. Both cations are undistor ted tetrahedra with bond lengths of 2.221(3) Angstrom for SbCl4+ and 2 .385(2) Angstrom for SbBr4+. The Raman spectra are consistent with und istorted SbX(4)(+) tetrahedra and have been assigned under T-d point s ymmetry. Trends within groups 15 and 17 are noted among the general va lence force constants of the PI4+ AsF4+, AsBr4+, AsI4+, SbCl4+ and SbB r4+ cations, which have been calculated for the first time, and the pr eviously determined force constants for NF4+, NCl4+, PF4+, PCl4+, PBr4 +, and AsCl4+, which have been recalculated for the P and As cations i n the present study. The SbCl4+ salt is stable in SO2ClF solution, whe reas the SbBr4+ salt decomposes slowly in SO2ClF at room temperature a nd rapidly in the presence of Br ion and in CH3CN solution at low temp eratures. The major products of the decompositions are SbBr2+Sb(OTeF5) (6)(-), as an adduct with CH3CN in CH3CN solvent, and Br-2.