Synthesis of tripodal aza crown ether calix[4]arenes and their supramolecular chemistry with transition-, alkali metal ions and anions

Tripodal aza crown ether calix[4]arenes, , , and , have been synthesized. The structure of protonated was elucidated by X-ray crystallography to be a self-threaded rotaxane. Complexation studies of and towards anions using Na+ as countercation were carried out by 1H NMR titration in dimethylsulfoxide-d6 and the mixture of chloroform-d and methanol-d4, respectively. Ligands and were able to form 1:1 complexes with Br−, I− and NO3− and the complexation stability varied as follows: NO3−>I−>Br−. The effect of countercation on anion complexation was also investigated. The results showed that the association constants of towards Br− in the presence of various cations varied as K+>Bu4N+>Na+. The enhancement in anion complexation ability of may result from the rearrangement of the tripodal ammonium unit in the presence of K+. The neutral forms, and , were able to form complexes with transition metal ions such as Co2+, Ni2+, Cu2+ and Zn2+. The stability of the complexes followed the sequence: Ni2+