A computational study of the conformations of the boric acid (B(OH)3), its conjugate base ((HO)2BO−) and borate anion (B(OH)4−)

The conformations of boric acid (1), its conjugate basis (2) and borate anion (3) have been investigated with the B3LYP, HF, MP2 and QCISD methods with a variety of basis sets. Transition-state structures connecting the various minima have been computed. Relative energies are reported at the G3(MP2)//B3LYP level of theory. The lowest-energy conformation of boric acid has C3h symmetry. The Cs conformer lies 4.1 kcal/mol higher in energy and the barrier for inter-conversion is 7.8 kcal/mol. The lowest-energy conformation of (HO)2BO− has C2v symmetry. There are two conformations lying higher in energy by 1.7 and 9.1 kcal/mol, with barriers of 7.8 and 10.3 kcal/mol, respectively. For borate anion two distinct S4-symmetry minima were located which differ in energy by 1.5 kcal/mol. The computed enthalpies of formation for 1, 2 and 3 are −236.3, −242.9 and −320.8 kcal/mol, respectively.