Synthesis, Metal Ion Complexation and Computational Studies of Thio Oxocrown Ethers

Abstract: The synthesis of some thio-oxocrown ether ligands, B1 (1,4-dithio-12-crown-4), B2 (1,7-dithio-12-crown-4), B3 (1,7-dithio-15-Crown-5), B4 (1,7-dithio-18-crown-6), B5 (1,10-dithio-18-crown-6), B6 (1,10-dithio-21-crown-7), under mild conditions, were reported. The ligands were characterized by FT-IR, ¹H NMR and GC-MS spectroscopy. The formation of 1:1 ligand complexes with a variety of metal salts (Ag⁺, Ca⁺², K⁺, Na⁺, Mg⁺², Zn⁺² and Fe⁺²) were investigated by a conductometric method in a 1:1 dioxane–water system at 25 °C, and the complexation constants (K_e = (Λ_MAm -Λ) / ((Λ-Λ_MaΛbAm) [L]) and free energy (∆G^o= - RT lnK_e) values are calculated. Details of the specific molecular interactions between the ligands and metals were proposed. We also performed DFT calculations to explain their geometrical properties, charges and frontier molecular orbitals.