Abstract or Keywords
Results of structural and thermochemical calculations involving boronic acid, HB(OH)(2), and the corresponding ethylene glycol ester, HB(-O-CH2-CH2-O-), in the presence of explicit NH3 and/or H2O molecules are reported. Calculations were performed in a polarizable continuum model (PCM) water solution and in the gas phase using density functional theory (DFT) and second-order Moller-Plesset perturbation theory (MP2) with the Dunning-Woon aug-cc-pVTZ basis set. Different classes of local minima on the HB(OH)(2)center dot NH3 center dot H2O and HB(-O-CH2-CH2-O-)center dot NH3 center dot H2O potential energy surfaces (PESs) in PCM water solution have been identified: (1) structures with a N -> B dative bond, [H3N -> BH(OH)(2)]center dot H2O, and [H3N -> B(H)(-O-CH2-CH2-O-)]center dot H2O, where the H2O is involved in hydrogen bonding; (2) water-inserted structures involving either a novel O -> B dative bond, H3N center dot H(H)O -> BH(OH)(2), and H3N center dot center dot center dot H(H)O -> B(H)(-O-CH2-CH2-O-) where the H2O molecule remains essentially intact or lower-energy zwitterionic arrangements in which a water H atom has been transferred to the ammonia, [H4N](+)[HO-BH(OH)(2)](-), and [H4N](+)[BH(OH)(-OCH2-CH2-O-)](-); (3) structures where both the NH3 and H2O molecules are exclusively involved in hydrogen bonding. In these simple model systems, arrangements with N -> B dative bonds, and some structures with only O center dot center dot center dot H and N center dot center dot center dot H hydrogen bonds, are ca. 5-6 kcal/mol lower in energy than either of the corresponding water-inserted structures.