Water/Aromatic Parallel Alignment Interactions. Significant Interactions at Large Horizontal Displacements

Analysis of crystal structures from the Cambridge Structural Database (CSD) and high level ab initio calculations reveals that the water/aromatic parallel alignment interactions, where the water molecule or one of its O–H bonds is parallel to the aromatic ring plane, can be significantly strong at large horizontal displacements. We found out that the strongest energies of the interactions are calculated for the water position with the large horizontal displacements, out of the aromatic ring and out of the C–H bond region. For calculated systems, normal distances were decreasing with increasing the horizontal displacement, in accord with the data found in crystal structures. The calculated energies of the interactions are significant, up to ΔE CCSD(T)(limit) = −10.25 kJ/mol (at a horizontal displacement of 2.6 Å), and comparable with the energy of the slipped-parallel benzene/benzene dimer. Both dispersion and electrostatic components of the interaction energy are important. The calculated interaction energies reveal that also at long horizontal displacements of 3.5 Å, interaction is substantially strong, up to ΔE CCSD(T)(limit) = −6.23 kJ/mol. The data show the existence of the water/aromatic parallel alignment interactions in crystal structures and indicate their importance for various systems.