Metal-oxygen complexes containing Cu,-Tl-, Hg-, Bi-and Pb-cations are electronically active in superconducting copper-oxides by stabilizing single phases with enhanced Tc, whereas other metaloxygen complexes deteriorate copper-oxide superconductivity. Cu, Tl, Hg, Bi, Pb in their actual oxidation states are closed shell d 10 or inert s 2 pair ions. Their electronic configurations have a strong tendency to polarize the oxygen environment. The closed shell d ions with low lying nd 10 ↔ nd 9 (n + 1)s excitations form linear complexes through d z 2 − s hybridization polarizing the apical oxygens. Comparatively low nd 9 (n + 1)s excitation energies distinguish Cu 1+,3+ , Tl 3+ , Hg 2+ from other closed shell d 10 ions deteriorating copper-oxide superconductivity, e.g. Zn