Oxalato-complexes

Zirconium oxalates exist as compounds, double compounds, and mixed oxalato complexes (165,195,225—226). When the carboxylate ligand is a longer alkyl chain, the materials often are called zirconium soaps. 

There is a wide range of diketonates, such as Ru(acac)3, with octahedral coordination [133b] (they do not seem, however, to be oxidized to the +4 state this is possible with osmium) similarly several salts of the tris(oxalato) complex Ru(C204)3 have been isolated. 

The reaction of the (necessarily) cis-oxalato complex with HCI in the last example, ensures the c/s-configuration for the chloro complex on recrystallization, the thermodynamically more stable fra s-isomer forms. fra s-Rupy4Cl2 has Ru-N 2.079 A and Ru—Cl 2.405 A. An imidazole complex (imH) tra s-[RuCl4(im)2] shows promise as a tumour inhibitor and is currently undergoing preclinical trials [135]. 

Of the various results, these appear to the reviewer to be the most meticulously obtained and they do not fit the other two rate laws suggested. At 25 °C n =. 0M perchlorate), = 5.10x10 l mole. sec" and = 4.78x10 l .mole" . sec . The corresponding reaction intermediates are a neutral chelate mono-oxalato complex and a (non-chelate) bis-oxalato complex of Cr(VI). 

It is interesting to juxtapose the reduction of a solid Fe(III)(hydr)oxide with a Fe(II) complex, e.g., with an oxalato complex of Fe(Il) (FenOx) on one hand with the oxidation of a Fe(II)bearing solid phase, e.g., a Fe(II) silicate with Fe(III) on the other hand (compare reactions (3) and (8), Table 9.1). In both cases the electron transfer (ET) occurs heterogeneously between Fe(III) and a Fe(II) complex. In one case the oxidant is the solid phase, in the other case the reductant is the solid phase. In simplified schematic notation ... 

Also, photolysis of dissolved iron(III) oxalato complexes, which are photolyzed with high quantum yields, has to be taken into account in order to describe this... 

Spectra of a variety of chromium compoimds in the +3 valence state are included in Fig. 16. The principal peak is centered at about 22-25 ev. in all cases. The CrjOa spectrum is almost identical to that of Mn02 of Fig. 5. Spectra of the oxalato complex and the ammonia complex are almost identical to spectra of the corresponding cobalt compounds of Figs. 13 and 11. 

Complexes with Oxyanion Ligands. The zirconium-peroxo-oxalato-complex [Zr(02)(C204 )(H20)2],3—4H2O, has been assigned the trans-diaquo octahedral structure (28) from spectroscopic and thermal studies. ... 

In addition to the partially oxidized tetracyanoplatinates, bis(oxalato)platinate-(II) can be nonstoichiometrically oxidized by chemical oxidants13 to form highly lustrous needlelike crystals containing platinum in the 2.36 oxidation state. These complexes have not been characterized to the extent of the tetracyano-platinate complexes however, the oxalato complexes are reported to be highly conducting.13 The starting material is bis(oxalato)platinate(II), which can be prepared in 30% yields from hexachloroplatinate(lV) and potassium oxalate.9... 

The salt K3[Cr(C204)] 3H20 is soluble in water. The crystals are dichroic, being green-blue by transmitted light and magenta by reflection. The infrared spectra of this and other tris(oxalato) complexes have been recorded and analyzed.17... 

Zuo, Y., and J. Hoigne, Formation of Hydrogen Peroxide and Depletion of Oxalic Acid in Atmospheric Water by Photolysis of Iron(III)-Oxalato Complexes, Environ. Sci. Technoi, 26, 1014-1022 (1992). 

I. Oxidation of Oxalato Complexes of Chromium(lll) by Cerium (IV) in Aqueous Sulfuric Acid... 

It was established that unreacted oxalato complex, Cr(OH2) +3, and free oxalate do not interfere in the titration. Thus the concentrations of cerium(IV) could be readily measured as a function of time. 

It is apparent that Cr(C2C>4)3 3, m-Cr(OH2)2(0204)2 , and Cr(0H2)4C2044 react smoothly with cerium(IV) in acidic-sulfate media, 1 mole of oxalate being oxidized for each 2 moles of cerium(IV) consumed. The observations made are consistent with the view that the three reactions proceed, at least initially, according to the stoichiometries represented by the respective Reactions 3,1, and 2. The initial absorbances of reactant solutions (values obtained by extrapolation of measured absorbances to zero time) agree well with the values calculated, on the basis of Beer s law, from the absorptivity coefficients of the components. Further, as the reactions in 1.83Af sulfuric acid proceed, the absorbances of the solutions move toward the values expected for the assumed products at rates which demonstrate the reactions are first order in cerium(IV) and complex—see, for example, Figure 2. We thus find no indication that reaction intermediates contribute measurably to the absorbances of reactant solutions, or that reaction conditions cause the rapid equilibration of any of the oxalato complexes with other species... 

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