A squaramide cage capable of binding and extracting H 2 PO 4 - and HP 2 O 7 3- in highly polar protic media.

A novel squaramide cage (2) binds H 2 PO 4 - and HP 2 O 7 3- with high selectivity and affinity in a highly polar protic solvent system. Receptor 2 is also able to extract these hydrophilic anions into a chloroform phase from water. The X-ray crystal structure demonstrated that compound 2 forms a complex with H 2 PO 4 - with 1 : 1 stoichiometry in the solid state.