Models metal-citrate complexation

The MPT model was also reported to apply in a number other electroless metal deposition systems, including a) electroless Ni from a citrate-complexant solution with dimethylamine borane (DMAB) reductant, operated at pH = 7 (pH adjusted using NH4OH) and at a temperature (T) = 40 °C [33] b) electroless Au deposition [34] from a KAu(CN)2 containing solution, which utilized potassium borohydride... 

Chemical models of metal-citrate aqueous complexation 382... 

CHEMICAL MODELS OF METAL-CITRATE AQUEOUS COMPLEXATION... 

Spin-coating of Mixed Citrate Complexes as a Versatile Route to Prepare Films of Transition Metal Multi-element Oxide Model Catalysts with Controlled Formulation and Crystalline Structure... 

Simple organic molecules such as small carboxylic acids (oxalate, acetate, malonate, citrate, etc.), amino acids and phenols are all ligands for metals. Such compounds may all occur as degradation products of organic matter in natural waters. The complexes formed are typically charged hydrophilic complexes. The stability of the metal complexes with these ligands is, however, moderate in most cases. Model calculations including such compounds at realistic concentrations indicate that their effects on speciation are relatively small [29],... 

The predicted waste inventory for the repository indicates that potentially significant quantities of the organic ligands—acetate, citrate, oxalate, and EDTA—will be present (US DOE, 1996). Actinide interactions with these compounds were not considered in the speciation and solubility modeling, as calculations suggested that they would be mostly complexed by transition metal ions (Fe, Ni " ", Cr, and Mn " ") released by corrosion of the steel waste containers and waste components. A thermodynamic model of actinide-ligand interactions appropriate to brines will be included in solubility calculations for WIPP recertification. 

The stoichiometry of the proton in Eqs. (10.7) and (10.8) (denoted by j) is a collective term that represents three possible configurations for the M Hy cit +- - (6Z ) complex. The value of j is 1 when Hc iP occurs in the complex, as in MHcif (6Z ). In this instance, a single carboxyl and the hydroxyl are protonated on the citrate molecule. Such complexes are significant only when solution pH values are less than 4. More commonly, j is zero or negative, the latter representing either the occurrence of H iciP in the complex (all citrate moieties ionized) [as in MH icit (ag)], or the occurrence of H ciP and a metal hydrolysis product in the complex [as in MOH(H icit)2 (ag)]. Chemical models derived from potentiometric acid-base titration studies cannot distinguish between the two potential proton sources (citrate hydroxyl or metal-bound water), as titrations... 

Gomez et al. " electrodeposited Co-Mo magnetic alloys from a sulfate-citrate bath on carbon electrodes. Although the focus of their paper was not on elucidating the mechanism of induced codeposition, it was suggested that hydrogen could not be responsible for the deposition of Mo in the Co-Mo system, because its concentration was fairly low and because another mechanism should explain the need for citrate or polycarboxylate anions in solution. The deposition process was foimd to be favored when molybdate was present in solution, even at very low concentrations. Hence, the authors adopted the model of Podlaha and Landolt, according to which a mixed-metal complex of cobalt(II), citrate and molybdenum dioxide is adsorbed on the surface and promotes Mo reduction. 

The apparent dissociation constants Kj(/9tO 7) which were compiled from the literature are given in Table 3.4 and they are presented together with the corresponding apparent Gibbs free energies AG =-R7 ln[Kj(/ 0 7)]. Similarly as with dissociation constants of citric acid in pnre water, differences in reported values of constants can be attributed not only to precision of experiments, but also to differences in applied speciation models, differences in mathematical form of equations used for activity coefficients and the choice of concentration scales (molar or molal). One aspect which was found to be extremely important was that earlier assumption that alkali metal cations do not form complexes with citrate anions is only partially correct. It was established that these cations form weak complexes with citrate anions and sometimes this interfering effect was even taken into account in calculation of Ki(/ 0 7) values [16, 21, 22]. 

Strouse J, Layten SW, Strouse CE (1977) Structual studies of transition metal complexes of triinized and tetraionized citrate. Models for the citrate ion to transition metal ion insolution and at the active site of aconitase. J Am Chem Soc 99 562-572... 

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