Electronic Properties, Conformational Flexibility, and Reactivity Descriptors of 1-(2'-Hydroxybenzylidene)-5-(1'-Pyridylethylidene)carbonohydrazone: A Combined DFT and Experimental Assessment
Arona Ngom
Laboratoire de Chimie Physique Organique et d’Analyses Environnementales, Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
Moussa Ndiaye
Laboratoire de Chimie Physique Organique et d’Analyses Environnementales, Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
Mohamed Lamine Sall *
Laboratoire de Chimie Physique Organique et d’Analyses Environnementales, Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
Mamadou Dieng
Laboratoire de Chimie Physique Organique et d’Analyses Environnementales, Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal and Department Physique et Chimie, Faculté des Sciences et technologies de l’Education et de la Formation, Université Cheikh Anta Diop, Dakar, Sénégal.
Thierno Moussa Seck
Laboratoire de Chimie de Coordination Organique et des Biomolécules Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
Abdoulaye Kone
Laboratoire de Chimie Physique Organique et d’Analyses Environnementales, Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
Ousmane Diouf
Laboratoire de Chimie de Coordination Organique et des Biomolécules Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
Modou Fall
Laboratoire de Chimie Physique Organique et d’Analyses Environnementales, Département de Chimie, Faculté des Sciences et Techniques, Université Cheikh Anta Diop, Dakar, Sénégal.
*Author to whom correspondence should be addressed.
Abstract
In this study, the structural and electronic properties, as well as the chemical reactivity, of the Schiff base hydrazone 1-(2'-hydroxybenzylidene)-5-(1'-pyridylethylidene)carbonohydrazone were comprehensively investigated using density functional theory (DFT) at the B3LYP/6-311G(d,p) level. Geometric optimisation revealed excellent agreement with experimental X-ray diffraction (XRD) data, confirming the quasi-coplanarity of the π-conjugated carbonohydrazone backbone and the presence of a stabilising intramolecular hydrogen bond (O18–H28⋯N3). A conformational discrepancy observed in the D(8,12,16,25) torsion angle (-24.60° calculated vs. 168.70° experimental) was explicitly attributed to crystal-packing forces and intermolecular interactions in the solid state. A frequency scaling factor of 0.967 was applied to the calculated harmonic vibrational frequencies, providing improved correlation with experimental FTIR spectra, particularly for the characteristic ν(C=O) (1675 cm-1 calc. vs. 1694 cm-1 exp.) and azomethine ν(C=N) (1615 cm-1 calc. vs. 1619 cm-1 exp.) bands. Mulliken atomic charge analysis, complemented by electrostatic potential considerations, highlighted potential nucleophilic sites on the electronegative heteroatoms (O18, N4, N1, O5) and electrophilic regions on the azomethine and carbonyl carbon centres. The investigation of frontier molecular orbitals (HOMO and LUMO) indicated efficient intramolecular charge transfer from the salicylaldehyde moiety towards the pyridine ring and the hydrazone backbone, with an energy gap (ΔE = 4.22 eV) reflecting high kinetic stability and moderate chemical polarisability. Global reactivity descriptors (I, A, η, S, χ, µ, ω), calculated within Koopmans' approximation, confirmed the overall electronic stability of the molecule.
Keywords: Carbonohydrazone, density functional theory, B3LYP/6-311G(d,p), Geometric parameters, Frequency scaling, Mulliken charges, Reactivity descriptors, Frontier molecular orbitals (HOMO–LUMO)