Crystal structure, Hirshfeld surface analysis and PIXEL calculations of the three isomeric (E)-2-((pyridinylmethylidene)hydrazinyl)benzo[d]thiazoles: Occurrence of stacking interactions

Abstract

Detailed structural analyses, utilizing crystal structure determinations, Hirshfeld surface analysis and PIXEL calculations have been carried out on the three isomeric (E)-2-((pyridin-X-ylmethylidene)hydrazinyl)-benzo[d]thiazoles: [1: 2-py] (X = 2), [1: 3-py] (X = 3), and [1: 4-py] (X = 4). All compounds are near planar with the largest deviation from planarity experienced by the pyridin-2-yl derivative. The bond lengths in the linker units between the terminal aromatic groups indicate a degree of electionic delocalisation is occurring, which thus points to an extended π system being present for each complete molecule. Hirshfeld surface analysis and the PLATON analysis provided information on the close contacts and intermolecular interactions. Each compound has its own set of intermolecular hydrogen bonds and stacking interactions. The total stabilization energies of the crystal packing, Etot, distributed as Coulombic (Ecoul,), polarization (Epol), dispersion (Edisp) and repulsion (Erep) components, are calculated by PIXEL. The energy contributions (kJ.mol−1) for each molecule, in the order, Edisp, Ecoul, Epol and Erep, are for compound [1: 2-py] -86.2, -43.8, -180.8 and 165.3 kJmol−1, for compound [1: 3-py] -98.4, -50.1, -188.4, 187.8 kJ.mol−1, and for compound [1: 4-py] – 88.9, -40.8, -194.9 and 164.5 kJ.mol−1 respectively. For [1: 2-py], [1: 3-py] and [1: 4-py], the number of motifs (molecule pairs) indicated by PIXEL to have energies above the cut-off value of -10 kJ.mol−are six, seven and seven, respectively. While the most energetically favourable motif in each compound is formed from N—H···N hydrogen bonds, with the ECoul term being the biggest contributor to Etot., different intermolecular hydrogen bonds are involved: the hydrogen bonds in [1: 2-py] and [1: 4-py], involve hydrazonyl moieties, ie. N—H(hydrazonyl)···N(hydrazonyl) with formation of R22(8) dimers, and in compound, [1: 3-py], C(7) chains are formed from N—H(hydrazonyl) ···N(pyridinyl) hydrogen bonds. The remaining motifs for all three compounds have Edisp as the biggest contributor to their stabilities. The percentage atom··· atom contacts were obtained from partial analysis of the PIXEL calculations: for both compounds [1: 2-py], [1: 3-py] and [1: 4-py], the three highest percentage atom···atom contacts were H···H (ca. 37%), H···C / C···H (ca.23%) and H···N/ N···H (ca. 17)%.