Novel C H•••O hydrogen-bonded supramolecular complexes of 18-crown-6 with 1-alkylpyridinium iodide and its amino derivatives: Third-order nonlinear optical properties and Hirshfeld surface analysis

Five supramolecular complexes of 18-crown-6 (18C6) with 1-alkylpyridinium iodide and its amino derivatives were synthesized successfully from methanolic solution by slow evaporation solution growth technique. Crystal structure elucidated by single-crystal X-ray diffraction reveals that all the cocrystals belong to the monoclinic system. Cocrystals bis(1-methylpyridinium iodide)-18C6 (I), bis(4-amino-1-methylpyridin-1-ium iodide)-18C6 (IV), and bis(4-amino-1-ethylpyridin-1-ium iodide)-18C6 (V) crystallize centrosymmetrically with space group C2/m and other two crystals bis(2-amino-1-methylpyridin-1-ium iodide)-18C6 (II) and bis(3-amino-1-methylpyridin-1-ium iodide)-18C6 (III) crystallize in P21/n centric space group. Intra- and inter-molecular hydrogen bonding interactions and weak Van der Walls forces construct the supramolecular architecture in the crystal packing. Interestingly, all the 1-alkylpyridin-1-ium cations interact with 18C6 moiety through C-H•••O hydrogen bonding interactions and N-H•••O interactions are observed only in the case of (II). Fingerprint plots of Hirshfeld surfaces were used to locate and analyze the percentage of hydrogen bonding interactions. Direct band gap energies are estimated using diffuse reflectance data by the application of the Kubelka – Munk algorithm. The third-order nonlinear optical susceptibilities (χ(3)) for the compounds are, 5.57 × 10−6 esu for (I), 3.62 × 10−6 esu for (II), 4.37 × 10−6 esu for (III), 5.30 × 10−6 esu for (IV), and 4.24 × 10−6 esu for (V), respectively.