Structural Characterization, Computational Investigation and Electrochemical Properties of 1-(2′-Hydroxy-3-methoxybenzylidene)-5-(1′-pyridylethylidene)-carbonohydrazide

Abstract

Asymmetric carbonohydrazide-derived Schiff bases have attracted increasing attention owing to their versatile coordination behaviour, tunable electronic properties, and potential applications in catalysis and bioactive metal-complex design. In this work, 1-(2'-hydroxy-3-methoxybenzylidene) -5-(1'-pyridylethylidene) -carbonohydrazide (H₃L²), an asymmetric Schiff base obtained by the condensation of carbohydrazide with o-vanillin and 2-acetylpyridine, was synthesised and comprehensively characterised. The crystal structure, determined by X-ray diffraction analysis, reveals a triclinic system (P-1) stabilised by a network of intra- and intermolecular hydrogen bonds. DFT calculations performed using the 6-31+G(d,p) basis set accurately reproduce the experimental geometric parameters and confirm the conjugated planarity of the molecule. Mulliken population analysis highlights the nucleophilic sites (O, N) as well as the polarisation of hydrogen bonds. The investigation of the frontier molecular orbitals HOMO and LUMO reveals an energy gap of 3.93 eV and a pronounced electrophilic character (ω = 25.55 eV). Global reactivity descriptors, particularly chemical hardness (η = 0.95 eV) and the high dipole moment (13.14 D), indicate moderate reactivity and strong electronic polarization favoring intermolecular interactions. FTIR spectroscopic characterisation is in good agreement with the calculated vibrational frequencies. Electrochemical studies performed by cyclic voltammetry reveal quasi-reversible electron transfer processes involving oxygen and nitrogen atoms, accompanied by remarkable stability in solution. Altogether, these structural, electronic, and electrochemical properties confer particular interest to this ligand as a promising candidate for the synthesis of metal complexes with potential biological or catalytic applications.