Lanthanum(III) Coordination Polymer Decorated With 2,1,3-Benzoxadiazole Units for Sensitive Luminescent Recognition of Sulfate Anion

One-dimensional coordination polymer La-CP, {[La(H₂O)₂(HL_O) (L_O)]·H₂O}_n containing a new luminescent ligand 4,7-di(4-carboxypyrazol-1-yl)-2,1,3-benzoxadiazole (H₂L_O) was synthesized. Upon excitation at 400 nm, the compound shows a strong emission with the maximum at 550 nm with high photoluminescence quantum yield of 43%. La-CP demonstrates sensing properties toward aluminum and gallium cations, as well as dihydrogen phosphate and sulfate anions through the emission enhancement response. The limits of detection were 0.42, 0.70, 0.37, and 0.40 μM, respectively. La-CP is the first example of a sensor for sulfate anion among all types of coordination polymers. The uptake of the analytes under the sensing conditions was evaluated, and a strong absorption enhancement as a result of such uptake was proposed as a probable emission response mechanism.