Structure and Bonding of a Novel Mercuracycle Complex Containing B-Hg Bonds at Carborane Vertices

The known compound 9-CF₃CO₂Hg-1,7-C₂B₁₀H₁₁, 3, was obtained by direct mercuration of l,7-C₂B₁₀H₁₂ (m-carborane) with 1 equiv of mercuric oxide in trifluoroacetic acid. Species 3 has now been fully characterized by multinuclear NMR and mass spectroscopy. A byproduct, 4, [(1,7-C₂B₁₀H₁₀)₂Hg₄(OH)₂][CF₃CO₂]₂, obtained from the reaction mixture was found in the solid state to be a cyclic array containing four mercury centers in which four trifluoroacetate anions interact simultaneously with each macrocycle. Two CF₃CO₂⁻ ions form a pair of hydrogen bonds with the (OH) ligands present in the macrocycle skeleton, and the remaining two trifluoroacetate anions interact with the cycle via moderately strong electrostatic interactions between Hg atoms and the oxygen atoms of the carboxylate groups. Each of the four trifluoroacetate anions is shared by two macrocycles to form a self-assembled 1:2 (mercury cycle to trifluoroacetate ion) polymeric array. Crystallographic data are as follows: triclinic, space group P1, a = 10.6113(8) Å, b = 11.1127(9) Å, c = 7.2044(5) Å, α = 74.826(2)°, β = 78.473(2)°, γ = 72.591(2)°, V = 775.53 ų, Ζ = 1, ϱ_calcd = 2.88 g cm⁻³, R = 0.049, R_w = 0.058.