Syntheses of ester and amide derivatives of calix[6]arene and their complexation affinities towards La³⁺, Eu³⁺, and Yb³⁺

One hexaester (1) and three hexaamide derivatives (2–4) of calix[6]arenes were prepared for the first time in one synthetic step, under microwave radiation. Compounds 2 and 3 were novel ones, while ester calix[6]arene derivative 1 and amide derivative 4 were prepared previously, by conventional syntheses. Microwave-assisted syntheses shortened the reaction times from 48 to 2 h. The binding properties of calix[6]arenes towards selected lanthanide cations (La³⁺, Eu³⁺, Yb³⁺) were studied by spectroscopic and mass spectrometric techniques. No complexation was observed with the ester derivative, while compounds 2–4 formed 1:1 complexes. Based on spectrophotometric titrations, the stability constants of resulting complexes could only be estimated (lg K ≥ 6). Calixarene derivatives, as well as their complexes, were analysed by ESI MS and MS/MS spectrometry. Corresponding fragmentation pathways were proposed, and in some cases confirmed by MS³ experiments. The results obtained by different techniques were in accordance.