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

The interactions of [Bu 4 N] 2 [B 10 H 10 ] and [Bu 4 N] 2 [B 12 H 12 ] with various proton donors (MeOH, EtOH, Pr i OH, PhOH, 4-FC 6 H 4 OH, 4-NO 2 C 6 H 4 OH, CF 3 CH 2 OH, (CF 3 ) 2 CHOH, (CF 3 ) 3 COH) in low polarity media were investigated. The site of coordination for [B 10 H 10 ] 2− and [B 12 H 12 ] 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 (Δ ν , Δ ν 1/2 , ΔA) and thermodynamic (Δ H °, Δ S °) characteristics of the H-complexes were determined. The BH⋯HO bonding strength increases from [B 12 H 12 ] 2− to [B 10 H 10 ] 2− . The geometry, energy, as well as electron distribution in the [B 10 H 10 ] 2− ·HOCH 3 , [B 10 H 10 ] 2− ·HOCF 3 , [B 10 H 10 ] 2− ·HCN, and [B 12 H 12 ] 2− ·HOCH 3 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.