Molecular clips based on benzoaza-15-crown-5 and diphenylglycoluril: synthesis and complexation with alkali and alkaline earth metal cations

New molecular clips were obtained by reacting benzoaza-15-crown-5 derivatives with diphenylglycoluril bis-ether in polyphosphoric acid. In the case of benzoaza-15-crown-5 with an unsubstituted nitrogen atom, a low yield of the target product was obtained. The introduction of substituents at the nitrogen atom allows the yield to be increased to 40–42%. It has been demonstrated that the complexing properties of the synthesized compounds depend on the nature of the substituent at the nitrogen atoms of the crown ether fragments. The unsubstituted clip interacts weakly with alkali metal cations but forms very stable 2:1 (L:M) complexes with alkaline earth metal cations. Among the alkali metal cations, the N–Me derivative forms the most stable complexes with K+ and Rb+, whereas the clip containing an ester group forms the most stable complex with the sodium cation.