CALORIMETRIC STUDY OF NI(II),ZN(II),CO(II )-N-(META-SUBSTITUTED PHENYL)IMINODIACETIC ACID NITRILOTRIACETIC ACID TERNARY-SYSTEMS

The protonation heats of N - (meta-substituted phenyl) iminodiacetic a cid (m - CH(3)PhIDA), the heats of formation of Ni(II), Zn(II), Co(II) - m -CH(3)PhIDA binary systems and Ni(II), Zn(II), Co(II) - m - CH(3) PhIDA - nitrilotriacetic acid (NTA) ternary systems have been determin ed in aqueous solution at 25.0+/-0.2 degrees C, I = 0.1 mol.dm(-3) (Na ClO4) by means of a model RD-1 automatic conduction calorimeter. To co mpare the formation heats for metal ions, we found that they obey Irvi ng-Williams order, i.e. Co(II) < Ni(II) > Zn(II). A supposed structure of the hydrated ligand has been offered to discuss the formation heat s of ternary complexes M(II) - m - CH(3)PhIDA - NTA and of binary comp lexes M(II) - m - CH(3)PhIDA.