PNNL

Abstract

Atomization energies at 0 K and heats of formation at 0 K and 298 K are predicted for the H(4-n)BXn- and the H(3-n)BXnF- compounds for (X = F, Cl, Br, I, NH2, OH, and SH) from coupled cluster theory (CCSD(T)) calculations with effective core potential correlation-consistent basis sets. In order to achieve near chemical accuracy (±1.0 kcal/mol), additional corrections were added to the complete basis set binding energies. The hydride, fluoride and X- affinities of the H(3-n)BXn compounds were predicted. Although the hydride and fluoride affinities differ somewhat in their magnitudes, they show very similar trends and are both suitable for judging the Lewis acidities of compounds. The only significant differences in their acidity strength orders are found for the boranes substituted with the strongly electron withdrawing and backdonating fluorine and hydroxyl ligands. The highest H- and F- affinities are found for BI3 and the lowest ones for B(NH2)3, and within the boron trihalide series the Lewis acidity increases monotonically with increasing atomic weight of the halogen, i.e., BI3 is a considerably stronger Lewis acid than BF3. For the X- affinities in the BX3, HBX2 and H2BX series, the fluorides show the highest values, while the amino and mercapto compounds show the lowest ones. Hydride and fluoride affinities trend linearly with the proton affinity of the anion of the X atom/group. Reasons for the correlation are discussed. This work was supported by the US Department of Energy Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.