Pyridine–Urea-Based Anion Receptor: Formation of Cyclic Sulfate–Water Hexamer and Dihydrogen Phosphate–Water Trimer in Hydrophobic Environment

A pyridine–urea-based receptor is found to stabilize cyclic sulfate–water hexamer [(SO4)2–(H2O)4]n4– and dihydrogen phosphate–water trimer [(H2PO4)2–H2O]n2– within its hydrophobic environment upon protonation. Anion–water clusters are stabilized by H-bonding arising from urea, water, and the pyridinium moiety. Thermal stability of anion–water clusters was established by TGA, and binding constants were determined by potentiometric titration.