Nickel solvent exchange data

Rate parameters for the reaction of nickel(II) with pyridine, bipyridine, phenanthroline, and terpyridine are available [118] for dimethyl-sulphoxide and acetonitrile solvents along with similar data for terpyridine in methanol and ethylene glycol (Table 12). To test whether or not substitution is normal in type, ligand substitution rate coefficients (fej) are compared with the respective solvent exchange rates (fes) by means of a ratio R defined as... 

The addition and dissociation of pyridine and substituted pyridine molecules to a planar nickel(II) complex with a quadridentate N202 ligand have been studied by the microwave temperature-jump technique in chlorobenzene solvent (38). The data were interpreted with the assumption of mechanism C (Fig. 7), i.e., that k65 is the smallest rate constant. Subsequently, however, 14N NMR was used to measure the rate of pyridine exchange from the octahedral complex (138). The rates are the same for the two different experiments within a factor of two. This observation excludes mechanism B and is consistent with either mechanism A or C. The rate constants have consequently been presented in Table VI as k64. 

The suppressor column, as well as enabling mercury to be determined, was also advantageous with respect to determination of copper, nickel, and in particular cobalt. Unfortunately, use of the suppressor column is detrimental to the determination of Cd(dtc)2 whose response disappears and Pb(dtc)2, whose response is considerably reduced. Presumably, these complexes are significantly retained as anionic complexes on the ion exchange suppressor. These data support conclusions obtained from voltammetric data in a conventional electrochemical cell, that the cadmium and lead complexes exist in anionic as well as neutral forms in the chromatographic solvent. Limits of detection for the simultaneous determination of lead, cadmium, mercury, copper, nickel and cobalt are given in Table 7.2. 

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