Reaction of 2,9-dioxo-1,4,7,10-tetraazabicyclo[1.10.1]hexadeca-1(11),13,15-triene-4,7-diacetic acid (H2L1) with CuCl2 · 2H2O in ethanol at pH 6 led to the monomeric benzodioxochlorocomplex [Cu(L′1)Cl] (1) (HL′1 = monoethylesther of H2L1). X-ray structural analysis has shown that in complex 1 the Cu is five-coordinated by two nitrogen and two oxygen atoms of the macrocycle and by a chloride, displaying a square pyramidal coordination geometry. One of the acetate arms does not coordinate to the Cu and has suffered an in situ ethanolic esterification reaction. The protonation constants of H2L1 and the stability constants of its complexes with Cu2+, Ni2+, Zn2+, Cd2+ and Pb2+ were determined by potentiometric methods and in some cases by 1H NMR spectroscopy. The stability constants of the complexes follow the trend [Ni(H−1L1)]− > [Cu(H−1L1)]− ≫ [Pb(H−1L1)]− > [Zn(H−1L1)]− > [Cd(H−1L1)]−, probably due to steric requirements. Spectroscopic measurements (absorption and EPR) at different pH values have shown the effect of the pH on the coordination sphere of the Cu complexes.