H – Bond interactions in water multimers and water multimers – Pyridine complexes: Natural bond orbital and reduced density gradient isosurface analyses

Abstract

Natural bond orbital and reduced density gradient isosurface analyses have been carried out on the water multimers of order n=1-9 and twenty-five complexes of Pyridine (Py) with water multimers of order n=1-5 optimized using density functional theory at B3LYP level of theory with the basis set 6–311++G(d,p). Among the twenty-five Py-Water structures, the seventeen configurations whose interaction energies are above 49 kJ/mol have been taken into consideration. The interaction (binding) energy values indicate that i) the 1(Py): 5 (water)/1:2 complexes are found to be the most/least stable networks and ii) the stability increases with increase in the number of water molecules in water multimers only. The occupancy and second order perturbation energy profiles suggest that O-H⋯N hydrogen bond is stronger than O-H⋯O, C-H⋯O and O-H⋯π hydrogen bonds. The non-classical hydrogen bonds and π→σ∗ interactions are also characterized by the green coloured regions in the reduced density gradient isosurfaces. The Shubin Liu energy decomposition (EDA-SBL) analysis shows that the water multimers and the Py-Water complexes are dominantly stabilized by the attractive electrostatic interactions. Of the two functionals, the B3LYP and ωB97XD, the latter which is meant for accounting the dispersion interaction disallows the O-H⋯π interaction between Py and water molecules and therefore, the former appears to give correct description on Py-Water interactions.