The heats of protonation of N-(p-substituted phenyl)iminodiacetic acids (B, R-phenyl-N(CH2COOH)(2), RPhIDA : R Is CH3O, CH3, H, Cl) and nitrilotriacetic aad (A, N(CH2COOH)(3), NTA) and the heats of formation of the M(II)-B and M(II)-A binary systems (M is Ni, Co, Zn), and of the M(II)-A-B ternary systems have been determined at 25.0 +/- 0.2 degrees C, I = 0.1 mol dm(-3) (NaClO4) in aqueous solution using an improved model RD-1 automatic conduction calorimeter. The entropies of protonation and of formation for these binary and ternary systems have been calculated from their free energies. The results show that both linear enthalpy relationships (LERs) and linear entropy relationships (LSRs) exist between the heat (and entropy) of protonation of B and the heat (and entropy) of formation of bath binary and ternary complex compounds. It is noted that the heats of protonation of RPhIDA and the heat of formation for their metal complexes are all positive, i.e. endothermic, and a hypothetical structure of the polyring for the hydrated ligands B has been suggested to interpret the experimental results.