Dihydrogen bonding of decahydro-closo-decaborate(2−) and dodecahydro-closo-dodecaborate(2−) anions with proton donors: experimental and theoretical investigation

The interactions of [Bu4N]2[B10H10] and [Bu4N]2[B12H12] with various proton donors (MeOH, EtOH, PriOH, PhOH, 4-FC6H4OH, 4-NO2C6H4OH, CF3CH2OH, (CF3)2CHOH, (CF3)3COH) in low polarity media were investigated. The site of coordination for [B10H10]2− and [B12H12]2− was found to be hydride hydrogen. Spectral (IR, NMR) evidences for the BH⋯HO hydrogen bonding between the boron hydrides and the OH proton donors in solution are presented. Spectral (Δν, Δν1/2, ΔA) and thermodynamic (ΔH°, ΔS°) characteristics of the H-complexes were determined. The BH⋯HO bonding strength increases from [B12H12]2− to [B10H10]2−. The geometry, energy, as well as electron distribution in the [B10H10]2−·HOCH3, [B10H10]2−·HOCF3, [B10H10]2−·HCN, and [B12H12]2−·HOCH3 complexes were studied using ab initio HF/6-31G approximation. It was shown that increase of the proton donor ability of acids leads to formation of bifurcate H-bonds.