Clustering of HClO4 with Bronsted (H2SO4, HClO4, HNO3) and Lewis acids BX3 (X = H, F, Cl, Br, OH): a DFT study

HClO4 is an important catalyst in organic chemistry, and also acts as a reservoir or sink species in atmospheric chlorine chemistry. In this study, we computationally investigate the interactions of Bronsted (H2SO4, HClO4, HNO3) and Lewis acids (BH3, BF3, BCl3, BBr3, B(OH)(3)) with HClO4 using the omega B97xD method and the aug-cc-pVDZ basis set. Different isomers of clusters with up to 4 molecules (tetramer) were optimized, and the most stable structures were determined. The enthalpies, Delta H, and Gibbs free energies, Delta G, of cluster formation were calculated in the gas phase at 298 K. Atoms in molecules (AIM) calculations find B-O bond critical points only in the (BH3)(n)HClO4 clusters, while formation of other clusters was based on hydrogen bonding interactions. (H2SO4)HClO4 and (B(OH)(3))HClO4, with formation enthalpies of -14.1 and -12.0 kcal mol(-1), were the most stable, and (BCl3)HClO4 with a formation enthalpy of -2.9 kcal mol(-1), was the least stable cluster among the dimers. Clustering of the Lewis and Bronsted acids with HClO4 enhanced its acidity, so that clustering of four HClO4 molecules and formation of (HClO4)(4) increases the acidity of HClO4 by about 35 kcal mol(-1). The most acidic dimer cluster found in the study was (BBr3)HClO4, with Delta H-acid of 275 kcal mol(-1); 26 kcal mol(-1) stronger than that of the HClO4 monomer.