The single-crystal X-ray structures of [XF6][Sb2F11] (X = Cl, Br, I) have been determined and represent the first detailed crystallographic study of salts containing the XF6+ cations. The three salts are isomorphous and crystallize in the monoclinic space group P2(1)/n with Z = 4: [CIF6][Sb2F11], a = 11.824(2) Angstrom, b = 8.434(2) Angstrom, c = 12.088(2) Angstrom, beta = 97.783(6)degrees, V = 1194.3(4) Angstrom3, R-1 = 0.0488 at -130 degreesC; [BrF6][Sb2F11], a = 11.931(2) Angstrom, b = 8.492(2) Angstrom, c = 12.103(2) Angstrom, beta = 97.558(4)degrees, V = 1215.5(4) Angstrom, R-1 = 0.0707 at -130 degreesC; [lF(6)][Sb2F11], a = 11.844(l) Angstrom, b = 8.617(1) Angstrom, c = 11.979(2) Angstrom, beta = 98.915(2)degrees, V = 1207.8(3) Angstrom3, R-1 = 0.0219 at -173 degreesC. The crystal structure of [lF(6)][Sb2F11] was also determined at -100 degreesC and was found to crystallize in the monoclinic space group P2(1)/rn with Z = 4, a = 11.885(l) Angstrom, b = 8.626(1) Angstrom, c = 12.000(1) Angstrom, beta = 98.44(1), V = 1216.9(2) Angstrom3, R-1 = 0.0635. The XF6+ cations have octahedral geometries with average Cl-F, Br-F, and I-F bond lengths of 1.550(4), 1.666(11) and 1.779(6) [-173 degreesC]/1.774(8) [-100 degreesC] Angstrom, respectively. The chemical shifts of the central quadrupolar nuclei, (CI)-C-35,37, Br-79,Br-81, and (127I), were determined for [CIF6][AsF6] (814 ppm), [BrF6][AsF6] (2080 ppm), and [IF6][Sb3F16] (3381 ppm) in anhydrous HF solution at 27 degreesC, and spin-inversion-recovery experiments were used to determine the T-1-relaxation times of (CI)-C-35 (1.32(3) s), (CI)-C-37 (2.58(6) S), Br-79 (24.6(4) MS), Br-81 (35.4(5) ms), and I-127 (6.53(1) ms). Trends among the central halogen chemical shifts and T-1-relaxation times of XF6+, XO4-, and X- are discussed. The isotropic (1)J-coupling constants and reduced coupling constants for the XF6+ cations and isoelectronic hexafluoro species of rows 3-6 are empirically assessed in terms of the relative contributions of the Fermi-contact, spin-dipolar, and spin-orbit mechanisms. Electronic structure calculations using Hartree-Fock, MP2, and local density functional methods were used to determine the energy-minimized gas-phase geometries, atomic charges, and Mayer bond orders of the XF6 cations. The calculated vibrational frequencies are in accord with the previously published assignments and experimental vibrational frequencies of the XF6+ cations. Bonding trends within the XF6+ cation series have been discussed in terms of natural bond orbital (NBO) analyses, the ligand close-packed (LCP) model, and the electron localization function (ELF).