Hydrogen-bonded supramolecular networks in hydrated nicotinoyl-hydrazones-based Derivatives with partial covalent character of O–H⋅⋅⋅N and O–H⋅⋅⋅O hydrogen bonds: Insights from X-ray and computational studies

We report a comprehensive experimental and theoretical investigation of two hydrated nicotinoyl-hydrazone
derivatives, (E)-N'-(1-(pyridine-4-yl)ethylidene)nicotinohydrazide dihydrate, 1⋅2H₂O and (E)-N'-(1-(pyridine-4-
yl)ethylidene)isonicotinohydrazide trihydrate 2⋅3H₂O, focusing on their supramolecular organization, hydrogenbonding
networks, and electronic properties. Single-crystal X-ray diffraction discloses distinct hydration motifs
and hydrogen-bond topologies arising from isomeric variation in the pyridyl substituent. Hirshfeld surface and
2D fingerprint analyses quantify contact contributions and highlight the roles of O–H⋅⋅⋅N, O–H⋅⋅⋅O, N–H⋅⋅⋅O, and
C–H⋅⋅⋅O/N interactions in crystal packing. Enrichment analysis further reveals the most preferred interactions
and the influence of the additional water molecule in compound 2. Energy decomposition using CLP-PIXEL and
DFT shows that water-mediated interactions are predominantly electrostatic, whereas dispersion governs weaker
π-stacking contacts. QTAIM topological analysis identifies partial covalent character in key O–H⋅⋅⋅N and O–H⋅⋅⋅O
hydrogen bonds, offering insight into their bonding nature and stability contributions. UV–Vis spectra supported
by TD-DFT calculations further correlate electronic transitions with frontier orbital distributions. This integrated
structural and computational study elucidates how hydration and isomerism modulate intermolecular interactions
and material stability in molecular assemblies relevant to liquid-like and hydrogen-bonded systems.