Theoretical studies on the first proton macroaffinity of Ni(II), Cu(II), Zn(II) and Cd(II) complexes of four triazacycloalkanes ([X]ane N3, X = 9-12): good correlations with the formation constants in solution.

A theoretical study on the first protonation step of Ni(ii), Cu(ii), Zn(ii) and Cd(ii) complexes of some triazacycloalkanes with general formula [X]ane N(3) (X = 9-12) is reported. The calculations were performed at DFT (B3LYP) level of theory, using LanL2DZ basis set. The DFT calculations were performed again using DZVP2 basis set for Ni(ii), Cu(ii) and Zn(ii) complexes and DZVP for Cd(ii) complexes. Once again, two kinds of our recently published definitions for gas-phase proton affinities of polybasic ligands, proton microaffinity and proton macroaffinity, were extended to their metal complexes. Among the 16 investigated complexes the most stable complex has both the smallest proton macroaffinity and macrobasicity. The least stable complex has also both the greatest proton macroaffinity and macrobasicity. In the case of each metal ion there are good correlations between the calculated gas-phase proton macroaffinities as well as macrobasicities of the corresponding complexes with their formation constants in solution.