Weakly bonded cluster structures of N,N′-dimethylethyleneurea and water

Abstract

Intermolecular interactions between a single water and two N,N′-dimethylethyleneurea (DMEU) molecules have been investigated using ab initio quantum chemistry method. The local and density-fitting approximations of the standard Møller–Plesset perturbation theory (DF-LMP2) have been employed together with the aug-cc-pVTZ basis set. Several trimeric systems were built where the water molecule, through the O–H⋯N hydrogen bond interactions, played the role of the bridge between the two DMEU molecules. The results show that the presence of the water molecule does not increase the stability of the trimeric systems. In the first three configurations the water molecule intercalates between two DMEU molecules, forming stable clusters. In the next three configurations, the water molecule is attached to a plane-parallel stacked DMEU dimer through the C=O⋯H–O hydrogen bond, and these structures are more stable than the first three. Small-angle neutron scattering data show clustering of DMEU molecules in their dilute aqueous solutions, and the ab initio results suggest that DMEU molecules could form contact pairs in dilute aqueous solutions.