Structure and stability of thiourea with water, DFT and MP2 calculations

The relative stabilities of thiourea in water are investigated computationally by considering thiourea-water complexes containing up to 1-6 water molecules (CS(NH2)(2)(...)(H2O)(n) (= 1-6)) using density functional theory and MP2 ab initio molecular orbital theory. The results show that the thiourea complex is stable and has an unusually high affinity for incoming water molecules. The clusters are progressively stabilized by the addition of water molecules, as indicated by the increasing of the binding energy. The binding energy of the cluster to each H2O molecule is about 33 U mol(-1) for n = 1-5. The C-S bond, N-C bond distance, Mulliken populations and binding energy keep approximately constant as the clusters increase in size with an increasing number of H2O molecules. As the solvation progresses, the C-S distance increases monotonically while the Mulliken populations on the C-S bond reduces monotonically with the addition of each H2O molecule, indicating that the C-S bond of the thiourea unit in the clusters is de-stabilized with an increasing number of H2O molecules. Charge transfers for the clusters are mainly found at N, S atoms of the thiourea. (c) 2005 Elsevier B.V. All rights reserved.