The enthalpies of dilution for aqueous solutions of [Co(cn)3)]Cl3, [Co(pn)3)]Cl3 and [Co(tn)3]Cl3, (whereen=1,2-diaminoethane,pn=1,2-diaminopropane, andtn=1,3-diaminopropane) have been measured at 298.15 K, and up to 1 mol kg−1+, using a new large isoperibol calorimeter by the “long-jump” method. Relative apparent molar enthalpies,291-01, have been extracted as an empirical equation relatingLΦ andm. We have compared our complex salts with the 3∶1 and 1∶3 aqueous systems found in the literature. Theoretical predictions for 1∶3 and 3∶1 electrolytes in the Restricted Primitive Model are also shown.