Electronic features and hydrogen bonding capacity of the sulfur acceptor in thioureido-based compounds. Part 2. Further insight by theoretical charge density study

Abstract

Theoretical charge density analysis of the thioureido based compound 4-methyl-3-thiosemicarbazide (MeTSC) is used in this study with the aim to provide additional insight into electronic features of the thioureido sulfur acceptor and the corresponding D-H...S hydrogen bonding (D=N, C). The present work is motivated by our earlier experimental charge density study on the same compound that pointed out to a great flexibility of the thioureido S acceptor and its ability to adjust the lone pair electron density to the donor groups in simultaneous hydrogen bonding. Through the additional theoretical approach we were able to single out different fragments of MeTSC crystal and to carefully follow the changes in electron density properties of the S acceptors belonging to: isolated MeTSC monomers (i.e. two crystallographically independent molecules), eight D-H...S bonded dimers and MeTSC molecules placed in full crystal environment, where each S atom engages in four hydrogen bonds. Deformation density of the sulfurs lone electron pair, topological properties of D-H...S interactions and electrostatic potential are here examined in order to comprehend the mutual influence and potential cooperative effects of the four simultaneously formed interactions to each of the S acceptors. The hydrogen bonding involving thioureido S acceptor is also investigated in terms of the energetic properties of the eight real MeTSC dimers existing in the crystal structure, and additional systems MeTSC/MeOH and acetone/MeOH. The latter systems are designed with the purpose of direct comparison and ranking of interactions involving thioureido S to those involving more conventional, carbonyl O acceptor. Energetic features were thoroughly studied through electrostatic interactions energies (XD2006), cohesive energies (CRYSTAL09) and ab initio approach employing the coupled-cluster single S and doubles augmented by a perturbational correction for connected triple excitations (CCSD(T)) method. (C) 2015 Elsevier B.V. All rights reserved.