Quantum chemical calculations are performed with Gaussian and molecular graphics are generated with GaussView . All geometries are optimized with Density Functional Theory (DFT) using the dispersion-corrected wB97XD functional with the 6-31+G(d) basis set where counterpoise calculations are used for complexes with more than one species to obtain basis set superposition error (BSSE) corrected energies. Solvent and dynamical effects are neglected. The choice of the 6-31+G(d) basis set can be regarded as an acceptable compromise between accuracy and speed. The addition of diffuse functions to the basis set is advised for an adequate description of molecular charges.