The stepwise formation constants of the complexes formed in the Cr2+-ethylenediamine (en), -malonate (mal), -glycinate (glyO), -β-alaninate (alaO), -iminodiacetate (imda), -nitrilotriacetate (nta), and -ethylenediaminetetra-acetate (edta) systems in aqueous 1 mol dm-3 KCl at 25 °C, determined pH-metrically, are as follows: log K1en = 5.48, log K2en = 4.15, log K1mal = 3.57, log K2mal = 1.92, log K1glyO = 4.21, log K2glyO = 3.06, log K1 alaO = 3.89, log K1 imda = 5.01, log K2imda = 3.17, log K1nta = 6.52, log K2nta = 3.14, log K 1edta = 12.70. The logarithm of the equilibrium constant for the Cr2+ = Cr(OH)+ + H+ process is -5.30; the formation of a protonated complex was detected in the Cr2+-malonate and -ethylenediaminetetra-acetate systems and the formation of a binuclear [Cr2(nta)]+ complex in the Cr2+ -nitrilotriacetate system. The log (K1/K2) values for the Cr2+ and Cu2+ complexes are roughly the same in the case of bidentate ligands, but they are much lower for Cr2+ than for Cu2+ in the case of multidentate ligands. The ratios of 'excess' stabilities of the Cr2+ and Cu2+ complexes are also roughly the same (0.54) in the case of bidentate ligands, but no excess stability (even destabilization) of the Cr2+ complexes was found in the case of the multidentate ligands. These phenomena are interpreted in terms of the difference in ionic radii of the two metal ions.
|Number of pages||4|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - Jan 1 1983|
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