Octahedral Coordination of Halide Ions (I^-, Br^-, Cl^-) Sandwich Bonded with Tridentate Mercuracarborand-3 Receptors

The “anti-crown” B-hexamethyl 9-mercuracarborand-3 (1) was shown to complex halide ions (I-, Br-, Cl-) in an η3-sandwich fashion. Symmetry-allowed interactions of the filled halide ion p-orbitals and the corresponding empty mercury p-orbitals result in three equivalent pHg−phalide−pHg three-center two-electron bonds and a sandwich structure. The molecular structures of [Li·(H2O)4][12·I]·2CH3CN, MePPh3[12·Br]·((CH3)2CO)2·(H2O)2, and PPN[12·Cl] were determined by single-crystal X-ray diffraction studies. Compound [Li·(H2O)4][12·I]·2CH3CN crystallized in the triclinic space group P1̄, a = 13.312(8) Å, b = 13.983(9) Å, c = 13.996(9) Å, α = 61.16(2)°, β = 82.34(2)°, γ = 86.58(2)°, V = 4365(2) Å3, Z = 1, R = 0.063, and Rw = 0.171. Compound MePPh3[12·Br]·((CH3)2CO)2·(H2O)2 crystallized in the monoclinic space group C2/c, a = 24.671(8) Å, b = 17.576(6) Å, c = 26.079(8) Å, β = 106.424(6)°, V = 10847(6) Å3, Z = 8, R = 0.0607, and Rw = 0.1506. Compound PPN[12·Cl] crystallized in the monoclinic space group C2/m, a = 37.27(2) Å, b = 29.25(1) Å, c = 10.990(4) Å, β = 100.659(7)°, V = 11774(8) Å3, Z = 4, R = 0.0911, and Rw = 0.2369.