The interaction of some N-substituted salicyl-aldimine-metal complexes with alkaline and ammonium ions is carefully investigated. The different species formed in solution are characterised by their stability constants and electronic spectra. The driving force of the adduct formation is attributed to the charge/dipole interaction and, where possible, to hydrogen bond formation. The stability constants are correlated to the nature of the ligand (bi- or tetra-dentate Schiff base), of the metal [Ni(II) or Co(II)], of the cation (alkaline or ammonium ions) and of the solvent (acetonitrile, tetrahydrofuran or 1,2-dimethoxyethane). In the case of the less inert complexes, the interaction with the ammonium reagents is followed by a rapid transimination or Schiff base release reaction. The prevalence of either reaction depends on the pK_a values of the co-ordinated Schiff base and ammonium ions. A new practical preparation method for the Schiff base metal [Ni(II), Cu(II), Co(II)] complexes is proposed, based on the transimination reaction between ammonium reagents and the iminic portion of metal chelates. The kinetic study suggests that the transimination reaction is biphasic: a fast addition of ammonium and a slow elimination of alkylammonium ions. On the other hand, the release reaction exhibits three distinct kinetic phases. The first fast reaction phase is attributed to the formation of adducts with the ammonium cations and to the conformational equilibrium shifts induced on the Ni complex. The other two reaction phases are assigned to the elimination of the two Schiff bases. Thus, in both cases, a different reactivity of identical ligands bonded to the same metal centre emerges.