Multiligand mixtures

Perdue, E.M. and Lytle, C.R. (1983a) A critical examination of metal-ligand complexation models application to defined multiligand mixtures. In Aquatic and Terrestrial Humic Materials (eds Christman, R.F. and Gjessing, E.T.). Ann Arbor Science, Ann Arbor, MI, pp. 295-313. 

The purpose of this paper is to present a model for single metal-multiligand solution equilibrium which quantitatively describes the net binding of metal ions to the multiligand mixture as a whole. Equally important aspects of this model are that it yields a unified conceptual visualization of complexation in complicated multiligand mixtures, and provides a framework for interpreting the results of experiments on such systems. The model, as presented here, will be confined to mononuclear complexes, and it is assumed that no solid phases are present. The influence of pH on the complexation reactions is described. The model is illustrated by simulation of various metal-multiligand systems, and the properties of these systems are represented by means of three-dimensional plots, called stability surfaces. 

These are called stability surfaces. The variation of the different solution properties during the course of an experimental run can then be depicted as the upward projection of the experimental path from the two-dimensional grid onto the surface. This conveniently allows one to simulate and pictorially represent the results of various types of experiments on metal-multiligand mixtures. ... 

The three-dimensional surfaces presented in Figures 3 and 4 relate to relatively simple multiligand mixtures (Tables I and III, respectively). Even such simple systems can become quite complicated if all of the possible equilibrium reactions are to be taken into consideration. These simple systems were chosen for illustration in this paper so that the reader could acquire a more complete appreciation of the total complexation system. However, this model is not limited to such simple cases, and we have applied it to multiligand mixtures and systems which are vastly more complicated than those described in Tables I and III. 

In recent years, largely through the efforts of Gamble and co-workers (Gamble, 1970, 1972 Burch et al., 1978) and MacCarthy and co-workers (Mac-Carthy, 1977 MacCarthy and Smith, 1979), the more important mathematical properties of multiligand mixtures have been presented. Perdue and Lytle (1983a,b) have extended these concepts and reviewed the mathematical details of determination of stability constants from laboratory data. Only a brief overview of the mathematics of proton binding is presented in this chapter. 

In a thorough paper that discusses many of the important properties of multiligand mixtures in the context of acid-base equilibria. Gamble (1970) has provided a direct method for estimating the distribution of pKa values in humic substances. Gamble assumes that a continuous distribution of nonidentical binding sites exists in humic substances and that the stoichiometric... 

MacCarthy, P. and Smith, G. C. (1979). Stability surface concept A quantitative model for complexation in multiligand mixtures. In Chemical Modeling in Aqueous Systems (E. A. Jenne, ed.). ACS Symp. Ser. No. 93, American Chemical Society, Washington, D.C., pp. 94-114. 

Perdue, M. P., and C. R. Lytle (1983), A Critical Examination of Metal-Ligand Complexation Models Application to Defined Multiligand Mixtures, in R. F. Christman and E. T. Gjessing, Eds., Aquatic and Terrestrial Humic Materials, Ann Arbor Science, Ann Arbor, MI, Chapter 14. 

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