Oxalate ligand, 82-3

Entry into the m-diammine system (Figure 2.50) uses the chelating ligand oxalate, as with the ammines use of NaBH4 as catalyst speeds this up. 

C20-0077. Several commercial rust removers contain the bidentate ligand oxalate, (O2 CC02) Explain how these household products remove rast. Include a structural drawing of the species that forms. 

Stability constants for calcium complexes of a selection of hydroxycarboxylate ligands are listed in Table VII (239,246,272-274). For tartrate, malate, and citrate stabilities decrease in the expected order Ca2+> Ba2+> Ra2+ (231,275). The stability constant for the complex of pyruvate (logiOifi 0.8 (273)) is similar to that for acetate calcium complexes of a-ketoglutarate and of oxaloacetate are somewhat more stable (logio-Ki = 1.3, 1.6 respectively (273)). The sequence logio-Ki = 3.0, 1.4, 1.1, 0.6 for the dicarboxylate ligands oxalate, malonate, succinate,... 

Using 0.1 M MgSC>4 solution which has a relaxation time less than 1 ps. The time constant of the set-up was found to be 60 6 ps. The relaxation times were measured over a range of concentrations of the reactants in order to determine the rate constants. The total ligand (oxalate) concentration was maintained at values which insured that only the first stage of complexation was important. 

To circumvent these issues, a relatively non-toxic metal salt was chosen as starting material along with a set of non-toxic ligands iron(III) nitrate and the ligands oxalate and citrate (Figure 2). 

Oxalate. A large number of actinide(VI) oxalate and mixed ligand oxalate complexes have been reported (see Table 46). Different coordination modes of uranyl by the oxalate group have... 

Whereas reactions of metal ions like Cu(II), Co(II), Mn(II) and Zn(II) are fast (these being labile complexes), metals ions like Ni(II) react somewhat slower, and Pt(II) much slower. Metals like Co(III), Rh(III), Cr(III) and Pt(II) are inert, and to make their reactions occur in a reasonable timeframe, it is often necessary to heat the reaction mixture. This is helpful because reactions typically double in rate for approximately every five degrees rise in temperature. An example is the inert red-purple RhC lg]3 ion, which reacts when boiled in aqueous solution with the chelating ligand oxalate (C2O42-) in approximately two hours to form yellow [RhtC CHb]3, whereas reaction at room temperature does not occur over reasonable time periods (6.7). 

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