HEXAKIS(PENTAFLUOROOXOTELLURATO)PNICTATE(V) ANIONS, M(OTEF5)(6)- (M=AS, SB, BI) - A SERIES OF VERY WEAKLY COORDINATING ANIONS

The weakly coordinating pnicogen anion series, M(OTeF5)(6-) (M = As, S b, Bi), has been synthesized as their tetraalkylammonium salts and hav e been structurally characterized by X-ray crystallography, F-19, As-7 5, Sb-121,Sb-123, Te-125, Bi-209 NMR spectroscopy, and Raman spectrosc opy. The following crystal structures are reported: N(CH3)(4)As-+(OTeF 5)(6-), trigonal system, space group <R(3)over bar>, a = 10.109(2) Ang strom, c = 55.443(18) Angstrom, V = 4907 Angstrom(3), D-calc = 3.209 g cm(-3), Z = 6, R = 0.0644; N(CH3)(4)Sb-+(OTeF5)(6-), monoclinic syste m, space group: C2/c, a = 17.875(3) Angstrom, b = 10.448(2) Angstrom, c = 19.752(2) Angstrom, beta = 110.83(1)degrees, V = 3447.8 Angstrom(3 ), D-calc = 3.135 g cm(-3), Z = 4, R = 0.0710; N(CH2CH3)(4)Sb-+(OTeF5) (6-), monoclinic system,space group C2/c, a = 10.506(3) Angstrom, b = 18.370(6) Angstrom, c = 20.352(7) Angstrom, beta = 91.23(2)degrees, V = 3926.9 Angstrom(3), D-calc = 2.848 g cm(-3), Z = 4, R = 0.0548; N(CH 3)(4)Bi-+(OTeF5)(6-), triclinic system, space group <P(1)over bar>, a = 8.945(2) Angstrom, b = 9.217(2) Angstrom, c = 10.029(2) Angstrom, al pha = 100.03(3)degrees, beta = 99.95(3)degrees, gamma = 98.06(3)degree s, V = 789.5 Angstrom(3), D-calc = 3.606 g cm(-3), Z = 1, R = 0.0456. The central pnicogen atoms of the anions are bonded octahedrally to th e six oxygen atoms and each of the six tellurium atoms is octahedrally bonded to an oxygen and five fluorines. Each anion structure can be d escribed as composed of an octahedron of octahedra. Average M-O bond d istances (corrected for libration) and M-O-Te bond angles are As-O = 1 .807 Angstrom, Sb-O = 1.96/1.91 Angstrom, Bi-O = 2.065 Angstrom and As -O-Te = 140(2)degrees, Sb-O-Te = 150.9(8)/162.8(9)degrees, Bi-O-Te = 1 36.2(3)degrees. Low electric field gradients at the pnicogen nuclei re sult in spin-lattice relaxation times which are sufficiently long to a llow for the observation of the NMR spectra of the four quadrupolar pn icogen nuclei and their couplings to Te-125. The anions are nonlabile on the NMR time scale in both SO2ClF and CH3CN solvents. Key frequenci es,in the Raman spectra of the three anions have been assigned. The M( OTeF5)(6-) anions are likely to be weaker OTeF5- donors and less basic than,current examples of weakly coordinating anion derivatives of the OTeF5 group, i.e., B(OTeF5)(4-), Pd(OTeF5)(4)(2-), Nd(OTeF5)(6-) and Ti(OTeF5)(6)(2-).