Synthesis and complexing ability of a new type of molecular clips based on diaza-18-crown-6 and diamino-dibenzo-18-crown-6 with pendant p-tert-butylcalix[4]arenes.

A convenient method for obtaining a new type of molecular clips based on diazacrown or diamino-dibenzocrown ethers with two calixarene molecules attached to a central fragment using an amide bonds has been developed. The synthesis and complexing properties of two representatives of this series - N,N'-bis(p-tert-butylcalix[4]arene-methoxycarbonyl)diaza-18-crown-6 (1) and N,N'-bis(p-tert-butylcalix[4]arene-methoxycarbonyl)-diamino-dibenzo-18-crown-6 (2) were demonstrated in this work. The complexing properties of the obtained compounds were evaluated through spectrophotometric titration method. A clip based on diaza-18-crown-6 forms 1:1 complexes with sodium, potassium and cesium cations (lgK_Cs<3) in the alkali metal series. At the same time, a clip 1 demonstrates exceptional selectivity toward barium cation in the alkaline earth metal series. The study of complex formation processes involving transition metal cations indicates that clip 1 forms the complexes 1:1 with cobalt, cadmium and lead cations, but with copper and iron this compound interacts with formation of 2:1 (L:M) complexes. A different behavior is typical for clip 2 based on diamido-dibenzo-18. With sodium cation 2 forms complexes 1:2 (L:M), the complex with the cesium cation is characterized by a high lgK value (>7), in the series of alkaline earth metals the formation of mononuclear complexes with relatively high stability constants (lgK 3.88-4.94) is observed for barium, strontium and calcium cations. On the contrary, clip 2 forms with the magnesium cations a binuclear complex with lgK₁₂ 5.75. The same compound in the series of transition metals interacts only with cations of copper, iron and cadmium to form 1:1 complexes with low values of stability constants.