Determination of stability constants for metal–ligand complexes using the voltammetric oxidation wave of the anion/ligand and the DeFord and Hume formalism

The voltammetric oxidation peaks for anions and other ligands that react at the Hg electrode can be used for the determination of stability constants of metal–ligand complexes using the DeFord and Hume formalism. Metal–ligand complexes with known stability constants that span the range of log β=2.9–5.9 were determined using the oxidation wave of the ligand as metal was varied. For the larger stability constants, it was possible to titrate concentrations of metal to ligand that are smaller than the ligand concentration and obtain reliable data (βjCxj approaches 1 in this case) indicating that an excess of titrant is not required to obtain reliable β values. Data reduction with different versions of the Solver tool (included with Microsoft Excel) is discussed and blind use of these programs without knowledge of the physical chemistry of the system is discouraged. The use of Solver gives β values that are in agreement with previous work that used (non)linear regression to evaluate each Fn(X) versus [X] function.