New calix[4]arene-monobenzo- and -dibenzo-crown-6 as cesium selective ionophores in the radioactive waste treatment: Synthesis, complexation and extraction properties

Cesium possesses two long lived isotopes Cs-135 and Cs-137 and the first one has a very long (2.3 x 10(6) y) half life and is one of the most mobile nuclides in a repository. Calix[4]arene-crowns-6 in the 1,3-alternate conformation are emerging as a new class of ionophores exhibiting a very high efficiency and selectivity in the complexation of cesium ion and its removal from highly acidic ([HNO3] = 3-4 M) radioactive waste having also high sodium nitrate concentration ([NaNO3] = 2-4 M). In order to improve both efficiency and cesium selectivity we have synthesised the novel calix[4]arene dibenzo-crowns-6 1 and 2 and the calix[4]arene-monobenzocrown-6 3 in 1,3-alternate conformation and evaluated their complexation properties towards alkali metal cations in homogeneous solution and in two phase systems, together with their performance in radioactive waste treatment. All data confirm the higher Cs/Na selectivity of the 1,3-alternate calix[4]crown-6 1-3 containing aromatic rings in the polyether loop, in comparison to previously synthesised compounds of the same series.