The "anti-crown" B-hexamethyl 9-mercuracarborand-3 (1) was shown to complex halide ions (I-, Br-, Cl-) in an eta (3)-sandwich fashion. Symmetry-allowed interactions of the filled halide ion p-orbitals and the corresponding empty mercury p-orbitals result in three equivalent p(Hg)-p(halide)-p(Hg) three-center two-electron bonds and a sandwich structure. The molecular structures of [Li . (H2O)(4)][1(2).I]. 2CH(3)CN, MePPh3[1(2). Br].((CH3)(2)CO)(2). (H2O)(2), and PPN[1(2). Cl] were determined by single-crystal X-ray diffraction studies. Compound [Li . (H2O)4][1(2).1]. 2CH(3)CN crystallized in the triclinic space group P (1) over bar, a = 13.312(8) Angstrom, b = 13.983(9) Angstrom, c = 13.996(9) Angstrom, alpha = 61.16(2), beta = 82.34(2), gamma = 86.58(2), V = 4365(2) Angstrom (3)(,) Z = 1, R = 0.063, and R-w = 0.171. Compound MePPh3[1(2). Br].((CH3)(2)CO)(2). (H2O)(2) crystallized in the monoclinic space group C2/c, a = 24.671(8) Angstrom, b = 17.576(6) Angstrom, c = 26.079(8) Angstrom, beta = 106.424(6), V = 10847(6) Angstrom (3), Z = 8, R = 0.0607, and R-w = 0.1506. Compound PPN[1(2). Cl] crystallized in the monoclinic space group C2/m, a = 37.27(2) Angstrom, b = 29.25(1) Angstrom, c = 10.990(4) Angstrom, beta = 100.659(7), V = 11774(8) Angstrom3, Z = 4, R = 0.0911, and R-w = 0.2369.