Solvothermal synthesis and theoretical study of a polypyridium trimesylate adduct

The title compound (C9H3O6·C20H17N4)4·0.5H2O 1 was isolated from solvothermal synthesis of 4′-(4-pyridyl)-2,2′:6′,2′-terpyridine (pytpy) and trimesic acid (1,3,5-benzenetricarboxylic acid, H3BTC). It was characterized by element analysis, IR, TGA, XRD, X-ray single-crystal diffraction, and spectroscopy properties, together with quantum chemistry calculation of spectrum (UV–vis spectra) through the method b3lyp/6–31 t g (d,p) are also investigated. Single-crystal X-ray diffraction shows 1 possesses a 3-D supramolecular network with 1-D six-fold helical double chains built from protonated (H3pytpy)\(_{n}^{3+}\) cations and deprotonated (BTC)\(_{n}^{3-}\) anions. The maximum of the fluorescent emission bands of 1 is located at 427 nm (λ ex = 266 nm), with a shoulder at about 390 nm. The result of theoretic calculations confirms that 1 has small HOMO–LUMO energy gap (1.24 eV) and high chemical reactivity.