a stepwise synthesis of three macrocyclic tetralactams selective complexants of Ca1+ vs. alkali and Mg2+ ions is reported. The multiplicity of the resonances in C-13 and F-19 n.m.r. spectroscopy is related to the restricted rotations around the carbon-nitrogen bond of the four amide moieties. The 1/1 complexes formed by addition of one equivalent of Ca(C10(4))2 exhibit very simple spectra which are assigned to the existence of a single form in the complex with the carbonyl oxygen atoms in the same orientation.