The influence of water molecule coordination onto the water–aromatic interaction. Strong interactions of water coordinating to a metal ion

The interactions between water molecules (non-coordinating and coordinating) and aromatic rings were studied by analyzing data in the Cambridge Structural Database and by quantum chemical calculations. The results show the influence of water coordination to a metal ion; interactions of coordinating water are stronger. The MP2/def2-QZVP interaction energies of non-coordinating water and neutral aqua complexes [ScCl3(H2O)3], [ZnCl2(H2O)4], [CdCl2(H2O)4], and [ZnCl2(H2O)2] with benzene molecule are −3.36, −5.10, −5.43, −6.86, and −5.14 kcal mol−1, respectively. Interactions of charged aqua complexes [ZnCl(H2O)5]+ and [Zn(H2O)6]2+ are stronger, −9.69 and −13.96 kcal mol−1, respectively. The calculations also reveal strong long-range interactions: at the distance of 3.0 A the interaction energies of neutral complexes are in the range of −4.11 to −4.91 kcal mol−1, while interaction energies of charged complexes are −6.37 and −10.76 kcal mol−1.