Metallacrowns composed of three Ru(alkylbenzene) units bridged by 2,3-pyridinediolate (pyO22−) are known to act as Li+-selective ionophores. In this study, we synthesized analogues with anisole and 3,5-dimethylanisole as the arene ligands, i.e., [{Ru(anisole)(pyO2)}3] and [{Ru(3,5-dimethylanisole)(pyO2)}3]. Their extraction properties for lithium and sodium picrates were investigated in a dichloromethane–water system at 25 °C. Compared to [{Ru(alkylbenzene)(pyO2)}3], the new metallacrowns allow faster and greater extraction of Li+ with much higher Li+/Na+ selectivity. [{Ru(3,5-dimethylanisole)(pyO2)}3] is superior to [{Ru(anisole)(pyO2)}3] in the Li+/Na+ selectivity. The extraction equilibrium constants and separation factors were determined for each system. The separation factor between Li+ and Na+ reaches 7.1 × 104 with [{Ru(3,5-dimethylanisole)(pyO2)}3]. The highly Li+-selective metallacrown was applied to the extraction separation of Li+ from seawater.
