The pentafluorooxotellurate compound ReO2(OTeF5)(3) has been synthesized from the reaction of ReO2F3 with B(OTeF5)(3) and structurally characterized in solution by F-19 and Te-125 NMR spectroscopy and in the solid state by Raman spectroscopy. The NMR and vibrational spectroscopic findings are consistent with a trigonal bipyramidal arrangement in which the oxygen atoms and an OTeF5 group occupy the equatorial plane. The F-19 and Te-125 NMR spectra show that the axial and equatorial OTeF5 groups of ReO2(OTeF5)(3) are fluxional and are consistent with intramolecular exchange by means of a pseudorotation. The Lewis acid behavior of ReO2(OTeF5)(3) is demonstrated by reaction with OTeF5-. The resulting cis-ReO2(OTeF5)(4)(-) anion was characterized as the tetramethylammonium salt in solution by F-19 and Te-125 NMR spectroscopy and in the solid state by Raman spectroscopy and X-ray crystallography. The compound crystallizes in the triclinic system, space group P (1) over bar, with a = 13.175(7) Angstrom, b = 13.811(5) Angstrom, c = 15.38(1) Angstrom, alpha = 72.36(5)degrees, beta = 68.17(5)degrees, gamma = 84.05(4)degrees, V = 2476(2) Angstrom(3), D-calc = 3.345 g cm(-3), Z = 4, R = 0.0547. The coordination sphere about Re-VII in cis-ReO2(OTeF5)(4)(-) is a pseudooctahedron in which the Re-O double bond oxygens are cis to one another.