MOLECULAR COMPLEXES BASED ON para-ALKYLSULFONIC ACIDS AND PYRIDINE DERIVATIVES: STRUCTURE AND MESOMORPHIC PROPERTIES

The paper presents the results of theoretical and experimental studies of new mesogenic molecular complexes based on 4-alkylsulfonic acids and 4-pyridyl-4'-n-alkyloxybenzoates. Using quantum chemistry methods (DFT), the structural units of the systems under study, which are hydrogen-bonded complexes, were modeled. The relationship between molecular parameters, electronic effects of substituents, gas-phase acidity and characteristics of the formed H-complexes is shown. Electron-donating alkyl substituents in the para-position of benzenesulfonic acid reduce gas-phase acidity compared to the unsubstituted molecule, enhancing the electron-withdrawing properties of the sulfo group. The type and potential barrier of the calculated potential functions of proton transfer from the sulfo group to the pyridine fragment in the molecular complexes under study allowed us to conclude that gas-phase acidity directly determines the characteristics of this process. It was found that para-alkyl-substituted benzenesulfonic acids form stronger hydrogen bonds in proton transfer complexes compared to unsubstituted benzenesulfonic acid. The synthesis of three samples of molecular complexes of 1:1 composition was performed (4-methylbenzenesulfonic acid : 4-pyridyl-4'-n-dodecyloxybenzoate, 4-ethylbenzenesulfonic acid : 4-pyridyl-4'-n-heptyloxybenzoate, 4-ethylbenzenesulfonic acid : 4-pyridyl-4'-n-dodecyloxybenzoate). IR spectra recorded at room temperature showed that the systems under study are H-complexes with proton transfer from the sulfo group to the pyridine fragment with an intermolecular hydrogen bond of the N–H∙∙∙O type. It was determined that all H-complexes have enantiotropic mesophorism, as evidenced by DSC and polarization thermomicroscopy data. The recorded mosaic textures in a polarizing microscope suggested that the samples under study had a smectic type of mesophase. It has been shown that the temperatures of phase transitions from the mesophase to the isotropic liquid phase depend on the length of the alkyl substituents in the components of the complexes, which may be a manifestation of the odd-even effect. For citation: Fedorov M.S., Filippov A.A., Syrbu S.A., Kiselev M.R. Molecular complexes based on para-alkylsulfonic acids and pyridine derivatives: structure and mesomorphic properties. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 12. P. 64-72. DOI: 10.6060/ivkkt.20246712.7094.