Tetrachloro- and tetrabromoarsonium(V) cations:: Raman and 75As, 19F NMR spectroscopic characterization and X-ray crystal structures of [AsCl4][As(OTeF5)6] and [AsBr4][AsF(OTeF5)5]

The salts [AsX4][As(OTeFs)(6)] and [AsBr4] [AsF(OTeF5)(5)] (X = Cl, Br) have been prepared by oxidation of AsX3 with XOTeF5 in the presence of the OTeF5 accepters As(OTeF5)(5) and AsF(OTeF5)(4). The mixed salts [AsCl4]Sb(OTeF5)(6-n)Cln-2 and [AsCl4][Sb(OTeF5)(6-n)Cl-n] (n greater than or equal to 2) have also been prepared. The AsBr4+ cation has been fully structurally characterized for the first time in SO2ClF solution by As-75 NMR spectroscopy and in the solid state by a single-crystal X-ray diffraction study of [AsBr4][AsF(OTeF5)(5)]: P (1) over tilde, a = 9.778(4) Angstrom, b = 17.731(7) Angstrom, c = 18.870(8) Angstrom, alpha = 103.53(4)degrees beta = 103.53(4)degrees gamma = 105.10(4)degrees, V= 2915(2) Angstrom(3), Z = 4, and R-1 = 0.0368 at -183 degrees C. The crystal structure determination and solution As-75 NMR study of the related [AsCl4][As(OTeF5)(6)] salt have also been carried out: [AsCl4][As(OTeF5)(6)], R (3) over bar, a = 9.8741(14) Angstrom, c = 55.301(11) Angstrom, V = 4669(1) Angstrom(3), Z = 6, and R-1 = 0.0438 at -123 degrees C; and R (3) over bar, a = 19.688(3) Angstrom, c = 55.264(11) Angstrom, V = 18552(5) Angstrom(3), z = 24, and R-1 = 0.1341 at -183 degrees C. The crystal structure of the As(OTeF5)(6)(-) salt reveals weaker interactions between the anion and cation than in the previously known AsF6- salt. The AsF(OTeF5)(5)(-) anion is reported for the first time and is also weakly coordinating with respect to the AsBr4+ cation. Both cations are undistorted tetrahedra with bond lengths of 2.041(5)-2.056(3) Angstrom fur AsCl4+ and 2.225(2)-2.236(2) Angstrom for AsBr4+. The Raman spectra are consistent with undistorted AsX4+ tetrahedra and have been assigned under T-d point symmetry. The Cl-35/Cl-37 isotope shifts have been observed and assigned for AsCl4+, and the geometrical parameters and vibrational frequencies of all known and presently unknown PnX(4)(+) (Pn = P, As, Sb, Bi; X = F, Cl, Br, I) cations have been calculated using density functional theory methods.