Experimental procedure stability constant determination

Procedure. The direct pH method described previously was used to determine the stability constants (13). The solutions used had a ligand to metal ratio of about 2 1 and the concentration level was about O.OOIM rare earth ion. All solutions were made up to ionic strength O.IM using potassium nitrate. Experimental data for one system are given in Table I. 

A SIT plot, for determination of the stability constant at / = 0, is given in Figure V-10. Water activity is explicitly taken into account. Most of the data in this plot ([56Z1E/CON], [75TR1/SCH] and [76VAS/LYT]) are obtained by re-evaluating experimental data. The re-evaluation procedure is documented in the corresponding entries in Appendix A and Appendix D. 

The experimental procedure is very similar to that used in [75LIB/TIA]. In the 1978 work, a potentiometric method was used to determine the stability constants of MBr complexes in M(C104)2 medium (M = Mn, Co, Ni and Zn ) at different concentrations. 

In addition to these limited procedures a number of experimental methods (vibrational spectroscopy, dipole moment measurements, electron diffraction, NMR, etc.) have been employed to determine the relative stabilities of these complexes.11,23 Intense effort has been directed towards establishing some kind of correlation between NMR parameters and stability of the borane complexes. The chemical shifts alone rarely show good correlation. However, complexation shifts (the chemical shift difference between the free and complexed borane or ligand) and various spin-spin coupling constants correlate better with calorimetric data, especially for ligands or boranes belonging to structurally similar series (Table 2).10,24... 

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