Positional Methoxy Substitution Effects on Crystal Packing, Electronic Structure, and Intermolecular Interactions in Two Schiff Base Isomers: A Combined SCXRD, TD-DFT, and Hirshfeld Surface Study
JOURNAL OF MOLECULAR STRUCTURE, cilt.1379, 2027 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 1379
- Basım Tarihi: 2027
- Doi Numarası: 10.1016/j.molstruc.2026.147282
- Dergi Adı: JOURNAL OF MOLECULAR STRUCTURE
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- Ondokuz Mayıs Üniversitesi Adresli: Evet
Özet
Two positional isomeric Schiff bases derived from 2-amino-3-methylphenol and methoxy-substituted salicylaldehydes were synthesized and comparatively investigated to evaluate the effect of methoxy substitution position on molecular geometry, electronic structure, crystal packing, and intermolecular interactions. Singlecrystal X-ray diffraction analysis revealed that Compound 1 crystallizes in the orthorhombic Pna2, space group, whereas Compound 2 adopts a monoclinic P2,/n structure. Compound 2 exhibited a slightly more planar geometry with a smaller dihedral angle between the aromatic rings, which is consistent with a modest increase in molecular conjugation. Experimental FT-IR, UV-Vis, 1H NMR, and 13C NMR analyses were supported by DFT calculations performed at the wB97X-D3/def2-TZVP level, while the electronic absorption spectra were investigated using TD-DFT calculations at the B3LYP/def2-TZVP level based on the wB97X-D3-optimized geometries. The calculated spectra showed good agreement with the experimental data and confirmed that the dominant electronic transitions are predominantly of tc -> tc* character. A bathochromic shift observed for Compound 2 was attributed primarily to the electronic influence of the methoxy substituent together with its slightly more planar molecular geometry. Hirshfeld surface, fingerprint plot, and energy framework analyses demonstrated that methoxy substitution position strongly influences intermolecular interaction patterns and supramolecular organization. Compound 1 forms a continuous three-dimensional interaction network stabilized by interchain C-H & sdot;& sdot;& sdot;O contacts, whereas Compound 2 exhibits a more distributed and heterogeneous interaction topology dominated by one-dimensional hydrogen-bonded chains. Energy framework calculations revealed that Compound 1 forms a cooperative three-dimensional interaction network comprising a dominant electrostatic interaction (Etot = - 61.7 kJ mol-1, Eele = - 72.5 kJ mol-1) together with a strong dispersion-driven interaction (Etot = -42.4 kJ mol-1, Edis = -74.4 kJ mol-1), whereas Compound 2 exhibits a more heterogeneous interaction topology characterized by localized electrostatic stabilization (Etot = - 47.3 kJ mol-1, Eele =- 87.7 kJ mol-1). Collectively, the combined experimental and theoretical results demonstrate that subtle methoxy positional isomerism significantly modulates electronic structure, crystal packing behavior, and intermolecular stabilization in Schiff base systems.