Persistent prevalence of supramolecular architectures of novel ultrasonically synthesized hydrazones due to hydrogen bonding [X–H⋯O; X=N]: Experimental and density functional theory analyses

Abstract

In this study, a series of novel pyridine-based hydrazone derivatives comprising (E)-2-((6-chloropyridin-2-yl)oxy)-N′-(2,3-dihydroxybenzylidene) acetohydrazide (CPBAH), (E)-2-((6-chloropyridin-2-yl)oxy)-N′-(4-fluorobenzylidene) acetohydrazide (CPFBH), (E)-N′-((4-chlorobenzylidene)-2-((6-chloropyridin-2-yl)oxy) acetohydrazide (CBCPH), and (E)-N′-(4-bromobenzylidene)-2-((6-chloropyridin-2-yl)oxy) acetohydrazide (BBCPH) were rapidly synthesized via ultrasonication at room temperature and their structures were unambiguously confirmed by spectral analysis and X-ray crystallography. Quantum chemical insights into the optimized geometry, nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), and natural bond orbitals (NBOs) were obtained for CPBAH, CPFBH, CBCPH, and BBCPH by density functional theory at the B3LYP/6-311G (d,p) level. Furthermore, NBO analysis was conducted at the ωB97XD/6-311G (d,p) level. Single crystal X-ray diffraction analyses showed that intra- and intermolecular attractive forces were responsible for structural stabilization. Indeed, the production of non-covalent directional interactions such as intra- and intermolecular hydrogen bonds is a key concept in materials architecture, where they depend mainly on small compact acceptors comprising nitrogen and oxygen atoms. Furthermore, the intra- and intermolecular hydrogen bonding networks (X–H⋯O; X = N) and conjugative interactions in the solid state were explored based on the NBOs and natural population analysis. Hirshfeld surface analysis was conducted to quantify the non-covalent interactions. CO⋯H–N intermolecular hydrogen bonds form the six-membered rings in CPBAH, CPFBH, CBCPH, and BBCPH. The crystal structures are also stabilized by C–H…Cg, C–F…Cg, and C–Cl…Cg interactions. The charge transfer processes in the compounds were estimated based on the FMOs. The highest occupied molecular orbital and lowest unoccupied molecular orbital energies were used to obtain the global reactivity parameters. Overall, the results calculated for CPBAH, CPFBH, CBCPH, and BBCPH were in excellent agreement with experimental data. The computational analyses also indicated that the compounds investigated have remarkable NLO properties.