Experimental Charge Density Evidence for the Existence of High Polarizability of the Electron Density of the Free Electron Pairs on the Sulfur Atom of the Thioureido Group, NH−C(S)−NH2, Induced by N−H···S and C−H···S Interactions

• Published in: Crystal growth & design 2007-02, Vol.7 (2), p.191-195
• Main Authors: Novaković, Sladjana B, Fraisse, Bernard, Bogdanović, Goran A, Spasojević-de Biré, Anne
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg060497+

The experimental charge density study of salicylaldehyde thiosemicarbazone (SalTSC) has been performed. The analysis of the crystal packing revealed that the sulfur atom is simultaneously engaged in six hydrogen-bonding interactions, two of the N−H···S and four of the C−H···S type. The strongest hydrogen bond, N2−H2n···S, leads to a centrosymmetric dimer. It has been established that the deformation density of the free electron pairs on the sulfur atom is inhomogeneously distributed within a torus. A relationship found between the deformation of the torus and the space directionality of the surrounding donor groups suggests that the sulfur atom of the thioureido moiety easily adjusts to the environment in order to increase the number of stabilizing contacts. A CSD study of the compounds containing a thioureido fragment, N−C(S)−N, confirmed the experimental results for SalTSC, i.e., about 60% of the 835 analyzed crystal structures form a dimer trough N−H···S interactions, whereas in about 50% of crystal structures, the S atom forms four of more D−H···S intermolecular interactions (D = C, N, or O).