New Calix[4]arene-Based Amides - Their Synthesis, Conformation, Complexation
New chiral calix[4]arene-based diol-diamides 1a , 1b , tetraamides 2a , 2b and 7 as well as achiral diamide 3 and tetraamides 4 - 6 were prepared. The conformation of 1 has been studied in solution by NMR and in solid state by X-ray crystallography. The pinched-cone conformation of the calix[4]arene skeleton in 1 was found to be stabilized by a circular array of hydrogen bonds formed by two phenolic O-H and two amidic N-H bonds at lower rim. Whereas no significant complexation of Na + was observed in solution for diamides 1 and 3 , tetraamides 2 , 4 , 5 , and 6 give strong complexes with Na + as confirmed by NMR titrations of 2 and 4 . The influence of anions and the solvents used on complexation ability of 2 towards Na + is negligible.