Divalent metal carbonate complexes, stability constants

Figure 6. Stability constants of some hi divalent metal carbonate complexes plotted against stability constants for the corresponding oxalate complexes. Data are from literature and are for 1 = 0. The equation of the line is log Kassoc (MCOs ) = 1.11 X log Kassoc (MC OA)-...

Not mentioned in Table 2 (and often not in the original papers ) is the optical form (chirality) of the amino acids used. All the amino acids, except for glycine (R = H), contain an asymmetric carbon atom (the C atom). In the majority of cases the optical form used, whether l, d or racemic dl, makes little difference to the stability constants, but there are some notable exceptions (vide infra). Examination of the data in Table 2 reveals (i) that the order of stability constants for the divalent transition metal ions follows the Irving-Williams series (ii) that for the divalent transition metal ions, with excess amino acid present at neutral pH, the predominant spedes is the neutral chelated M(aa)2 complex (iii) that the species formed reflect the stereochemical preferences of the metal ions, e.g. for Cu 1 a 2 1 complex readily forms but not a 3 1 ligand metal complex (see Volume 5, Chapter 53). Confirmation of the species proposed from analysis of potentiometric data and information on the mode of bonding in solution has involved the use of an impressive array of spectroscopic techniques, e.g. UV/visible, IR, ESR, NMR, CD and MCD (magnetic circular dichroism). 

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