The Lewis acid behavior of Te(OTeF5)4(4) toward the OTeF5- anion has been investigated, and the resulting Te(OTeF5)(5)(-) and FTe(OTeF5)(4)(-) anions have been structurally characterized in solution as the tetramethylammonium and tetraethylammonium salts by F-19 and Te-125 NMR spectroscopy. The crystal structures and Raman spectra are reported for Te(OTeF5)(4) and N(CH3)(4)Te-+(OTeF5)(5)(-). The former compound crystallizes in the triclinic system, space group P (1) over bar, with a 9.502(3) Angstrom, b = 9.748(5) Angstrom, c 10.603(4) Angstrom, alpha = 85.73(4)degrees, beta = 72.50(3)degrees, and gamma. = 71.26(3)degrees at -97 degrees C; V = 886.7(6) Angstrom(3); D-calc = 4.052 g cm(-3) for Z = 2; R(1) = 0.0239. The salt, N(CH3)(4)Te-+(OTeF5)(5)(-), crystallizes in the orthorhombic system, space group Pbca, with a 11.021(2) Angstrom, b = 20.096(5) Angstrom, c = 27.497(5) Angstrom at 24 degrees C; V = 6090(2) Angstrom(3); D-calc = 3.042 g cm(-3) for Z = 8; wR = 0.0781. The Te(OTeF5)(4) molecule is a disphenoid and is consistent with an AX(4)E VSEPR geometry in which a lone electron pair and two OTeF5 groups occupy the equatorial plane and two OTeF5 groups occupy the axial positions of a trigonal bipyramid. Two secondary Te-IV... F contacts arising from two nearest neighbor Te(OTeF5)4 molecules give rise to a chain structure in which the coordination about Te-IV is best described as a distorted octahedral (AX(4)Y(2)E) VSEPR arrangement. The central Te-IV atom of the Te(OTeF5)(5)(-) anion is bonded to five OTeF5 groups, so that the gross geometry about the Te-IV atom can be described as pseudo-octahedral. The presence of a bulky OTeF5 group in the axial position influences the conformational relationships of the equatorial OTeF5 groups. Solution NMR studies establish that the FTe(OTeF5)(4)(-) anion is pseudo-octahedral about the : Te-IV atom and that the fluorine bonded to Te-IV is in the axial position opposite the lone electron pair. The coordination in the Te-IV valence shells of the Te(OTeF5)(5)(-) and FTe(OTeF5)(4)(-) anions is consistent with an AX(5)E VSEPR arrangement of five bond pairs and a lone electron pair. The Te(OTeF5)(5)(-) and TeF5- anions were shown to undergo ligand redistribution and, with the exception of FTe(OTeF5)(4)(-), the intermediate FnTe(OTeF5)(5-n)(-) anions were found to be labile on the NMR time scale.