Tetraaza complexes with M2+ were produced in the gas phase by Electrospray (ESI) of solutions containing salts of M2+ dinitrates and a tetraaza compound such as cyclam. The complex CyclM(2+) formed in solution and transferred to the gas phase via ESI was introduced into a reaction chamber containing known partial pressures of a ligand L. Equilibria between CyclM(2+) and L establish CyclML(n)(2+) = CyclML(n-1)(2+) + L and the equilibrium constants K-n,K-n-1 are determined with a mass spectrometer. Determinations at different temperatures lead to not only the Delta G(0) (n,n-1) values but also the Delta H-n,n-1(0) and Delta S-n,n-1(0) values. Data for n = 1, 2, and 3 were obtained for L = H2O and CH3OH. The Delta G(1,0)(0), Delta H-1,0(0) as well as Delta G(2,1)(0), Delta H-2,1(0) values, when M2+ = Mn2+ and Zn2+, were larger than those for Ni2+ and Cu2+. The ligand field theory and the Irvine-Williams series predict a reverse order, i.e., stronger bonding with Ni2+ and Cu2+ for simple ligand reactions with M2+. An examination of the differences of the reactions in solution and gas phase provides a rationale for the observed reverse order for the CyclM(2+) + L reactions. Differences between gas phase and solution are found also when M2+ = Cu2+, but the tetraaza macrocycle is changed from, 12-ane to 14-ane to 15-ane. The strongest bonding in solution is with the 14-ane while in the gas phase it is with the 15-ane. Bond free energies, Delta G(1,0)(0), for CyclCu(2+) with L = H2O, CH3OH, NH3, C2H5OH, C3H7OH, (C2H5)(2)O, and CH3COCH3, are found to increase in the above order. The order and magnitude of the Delta G(1,0)(0) values is close to Delta G(1,0)(0) values observed with potassium K+ and the same ligands. These results show that the cyclam in CyclCu(2+) leads to an extensive shielding of the +2 charge of Cu2+. Ligands with gas phase basicities that are relatively high, lead to deprotonation of CyclM(2+). The deprotonation varies with the nature of M2+ and provides information on the extent of electron transfer from the N atoms of the cyclam, to the M2+ ions.