DIVALENT TRANSITION METAL COMPLEXES OF HYDROLYZED ETHYLENE-MALEIC ANHYDRIDE COPOLYMER

In the alternating 1:1 copolymer of ethylene and maleic acid with molecular weight of 20,000-30,000, the two carboxyl groups have very different pk values; both are larger than those of succinic acid. Formation constants have been measured potentiometrically for the complexes between this copolymer and manganese(II), cobalt(II), nickel(II), copper(II), zinc(II), and cadmium(II) ions. The interionic attraction theory of electrolytes was useful in treatment of the data. The values are much larger than those previously reported for analogous systems in media of high ionic strength, where complexation occurs with the cation of the added electrolyte. A comparison is made with the corresponding metal-monosuccinate complexes; the differences in stabilities are discussed in terms of the enthalpy and entropy of complex formation.