The kinetics of the metal exchange reactions between (5-R-phen)copper(II) (R = Me, H, Cl, and NO2) and Ni(II) was studied at 25?and ionic strength 1.0 mol dm-3 or pH 2.3-3.5. The rate of the exchange reactions was measured by a spectrophotometer. The reactions appeared to proceed through 3 different pathways which involved H+ attack and Ni attack as well as a pH- and Ni-independent dissociation of the complexes. The kinetics conforms to the following rate law: d[Ni(5-R-phen)]/dt = (kp + kH[H+] + kNi[Ni2+])[(Cu(5-R-phen)2+]. The reaction rate of the 3 pathways increased with decreasing basicity of the ligand. Some linear free energy relationships were found to exist between the reactivity of these Cu(II) complexes and the base strength of the ligand 5-R-phen. The mechanisms of the reactions are discussed.

Key words: REACTION MECHANISM, COPPER COMPLEX, EQUILIBRIUM CONSTANT, EXCHANGE REACTION, NICKEL COMPLEX, REACTION RATE CONSTANT, PHENANTHROLINE, LINEAR FREE ENERGY RELATIONSHIP