Interaction of metal ions with two new calix[4,8]arene derivatives

Two new calixarene derivatives: 5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis-(piperidinocarbonylmethyoxy)calix[4]arene (L-4) and 5,11,17,23,29,35,41,47-octa-t-butyl-49,50,51,51,53,54,55, 56-octa-(piperidinocarbonylmethoxy)calix[8]arene (L-8), which show good binding abilities to metal ions, were synthesized by the reaction of the corresponding calixarene derivatives with piperidine. The ligand L4 is capable of separating a tight ion-pair formed by Pb2+ and the picrate anion in THF. The interactions of the new ligands (L-n n=4, 8) with Na+, Pb2+ and Cd2+, in the presence or absence of picrate, were investigated by H-1 NMR and electrospray mass spectrometry. It is found that L4 reacts with these metal ions to form a unique complex which ran be described as [M-m + L-4](m+) while L-8 forms a variety of complexes depending on whether there are picrate anions in solution. [(Mm+L8)]m(+) is formed in the absence of the picrate, and two complexes, [PbL8] . CH3CN . H2O and [PbNaL8](3+), are formed in the presence of the picrate. The higher conformational flexibility and larger macro-ring size of Ls account for the fact that it forms a variety of complexes as compared with L-4.