Computational Study on the Characteristics of the Interaction in Linear Urea Clusters

Quantum mechanics calculations were applied to investigate the N-H center dot center dot center dot O hydrogen bonding properties in linear (urea)(n-1-10) clusters. We investigated geometries, binding energies, and O-17 chemical shielding tensors of urea clusters, by means of MP2 and DFT methods. The charge-transfer character of the urea clusters was estimated using Natural Bonding Orbital characteristics. It was found that the cooperativity effects enhance significantly the N-H center dot center dot center dot O hydrogen bond from -33.08 (dimer) to -47.67 kJ/mol (decamer). The n-dependent trend of O-17 shielding tensors was reasonably correlated with cooperative effects in r(C-O) bond distance. To deepen the nature of the interaction in urea clusters, the scheme of decomposition of the interaction energies was applied using Morokuma analysis and a variant of symmetry-adapted perturbation theory (SAPT) based on DFT description of monomers, referred to as SAPT-DFT. The SAPT-DFT analysis of the interaction energy components indicates that the electrostatic and dispersive interactions are the most important attractive terms in the urea dimer. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3184-3195, 2011