A combined experimental and theoretical electron density study of intra- and intermolecular interactions in thiourea S,S-dioxide

The thiourea SS-dioxide molecule is recognized as a zwitterion with a high dipole moment and an unusually long C-S bond. The molecule has a most interesting set of intermolecular interactions in the crystalline state-a relatively strong (OH)-H-...-N hydrogen bond and very weak intermolecular (CS)-S-... and (NO)-O-... interactions. The molecule has C, symmetry, and each oxygen atom is hydrogen-bonded to two hydrogen atoms with (OH)-H-...-N distances of 2.837 and 2.826 Angstrom and angles of 176.61 and 158.38degrees. The electron density distribution is obtained both from X-ray diffraction data at 110 K and from a periodic density functional theory (DFT) calculation. Bond characterization is made in terms of the analysis of topological properties. The covalent characters of the C-N, N-H, C-S, and S-O bonds are apparent, and the agreement on the topological properties between experiment and theory is adequate. The features of the Laplacian distributions, bond paths, and atomic domains are comparable. In a systematic approach, DFT calculations are performed based on a monomer, a dimer, a heptamer, and a crystal to see the effect on the electron density distribution due to the intermolecular interactions. The dipole moment of the molecule is enhanced in the solid state. The typical values Of rho(b) and H-b of the hydrogen bonds and weak intermolecular (CS)-S-... and (NO)-O-... interactions are given. All the interactions are verified by the location of the bond critical point and its associated topological properties. The isovalue surface of Laplacian charge density and the detailed atomic graph around each atomic site reveal the shape of the valence-shell charge concentration and provide a reasonable interpretation of the bonding of each atom.