Eight proton di-ionisable diacid conformers of nano-baskets including 25,26-di(carboxymethoxy)calix[4]arene-crown-3, -crown-4, -crown-5 and -crown-6 in the cone conformation have been synthesised and shown to extract lanthanide cations effectively. Their selectivities were greatly influenced by the acidity of the solution and the conformations of the calix-crown. The extraction loading was improved by having the p-tert-butyl-moiety in the upper rim. The scaffold bearing the crown-4 ether moiety showed the least loading, while scaffolds with crown-3- and crown-5-ether moieties had the best selectivities.