Molecular Hydrogen as a Proton Donor in HH···F Hydrogen Bonds—BF₄⁻···(H₂)_<i>n</i> Clusters

The MP2/6-311++G(d,p) calculations are performed to analyze geometric, energetic, and topological parameters of BF₄ ^-···(H₂)_n clusters (n up to 8). These analyses are supported by the Natural Bond Orbitals method and the Quantum Theory in Atoms in Molecules approach. The BF₄ ^- anion acts as the Lewis base since its whole molecular surface is characterized by the negative electrostatic potential. The hydrogen molecules in clusters are considered to play the role of Lewis acid ligands. These ligands are located linearly in directions being the elongation of BF bonds if the number of H₂ molecules in the cluster does not exceed 4. For the greater clusters (n ≥ 5), all H₂ molecules tend to form linear HH···F arrangements, or nearly so. However, the BF···H angles are sometimes far from linearity. The HH···F interactions may be classified as hydrogen bonds; the analysis of such interactions is also performed.