Charge Density Analysis of 2-Pyridineformamide N(4)-Methylthiosemicarbazone (Z =4): Role of an Enhanced N-H center dot center dot center dot S Thioureido Dimer

Abstract

Charge density distribution in 2-pyridineformamide N(4)-methylthiosemicarbazone (TSC4) has been determined using high-resolution X-ray diffraction data (100 K) and Hansen-Coppens multipole formalism. The results are interpreted in terms of Baders quantum theory of atoms in molecules (QTAIM), electrostatic potential analysis, and theoretical calculations (CRYSTAL09). The study highlights the molecular diSsimilarity at the electronic level. The N-H center dot center dot center dot S interactions have a dominant role in Stabilization of the TSC4 crystal Structure. As each of the four S acceptors simultaneously engages in several interactions, the focus of study is on the lone pairs electron density of these acceptors which is particularly able to adjust to the various spatial distributions of the interacting donor groups. The main structural feature of TSC4 is the formation of specific N-H center dot center dot center dot S bonded dimers between two pairs of independent molecules. These dimers are the main building block in the orkstal structure, and with the two additional N-H center dot center dot center dot S contacts they represent a significant enhancement of a typical R-2(2)(8) dirtier synthon which dominates among the thioureido-based crystal structures. Two TSC4 dimers are structurally very similar and exhibit considerable cohesive energy (-20.8 and 21.4 kcal/mol). This: type of dimer is the only structural motif that is common for S acceptors of all four independent molecules.