Preparation of coordination polymers with 8-hydroxyquinolineazobenzensulfonic acid as a planar multidentate ligand and the study of their photochemical and photo-stability properties

Abstract

The combination of ditopic ligand 4-(8-hydroxyquinoline-5-azo)-benzensulfonic acid (H₂QBS) with metal ions (M = Na⁺, Pb²⁺, Zn²⁺, Mn²⁺, Cd²⁺) leads to five different coordination polymers (CPs): [Na₂(QBS)(H₂O)₂]_n (1, 3D framework), {[Pb(QBS)(DMSO)]·2(ⁱPrOH)}_n (2·2ⁱPrOH, 2D layer), {[Zn(QBS)(DMSO)]·2DMSO}_n (3·2DMSO, 1D chain), [Mn(QBS)(ⁱPrOH)(DMSO)]_n (4, 1D ladder), and [Cd₂(QBS)₂(DMSO)₂(H₂O)₄]_n (5, 1D chain). All compounds were characterized by FT-IR, elemental analysis and TG analysis, and their structures were determined by single crystal X-ray diffraction. As expected, H₂QBS acted as a multimode ligand and the azo bond in the trans-form existed in all compounds. Their photo-stability was also studied using irradiation from different light sources (450 nm, 365 nm and 254 nm). Under blue light (450 nm) and lower energy UV light (365 nm), the colors of all compounds were well preserved and the absorption spectra show slight changes. However, when irradiated using higher energy UV light (254 nm), the coordination interaction between the metal ions and the ligand was disassociated and the color faded.