Oxalate ion complexes

As the result of oxalate ion complexing of Al3+, precipitation of Am-Cm-A1(N03)3 solutions was not straightforward. Using Dy as a stand-in for Am-Cm, simulated solutions were prepared where the ratio of A1(N03>3 to Dy (1 03)3, KF, NaN03, and Hg(1 03)2 was held constant as would result in actual process solutions. However, the total ratio of these species to free nitric acid was varied in the stock solutions. Precipitation conditions were simulated by additions of either a half-equal or an equal volume of either an 0.9M or a saturated ( 2M) potassium oxalate... 

Rust stain removal involves forming a water soluble oxalate ion complex of iron like pe(C204)3]. The overall reaction is ... 

Tetravalent vanadium forms a large number of complexes, all of which involve the vanadyl group, VO, and most of which are ato- complexes. The most common oxalato complex is H2(V0)2(C204)3, which can give a positive test for the presence of the oxalate ion in aqueous solutions. Aqueous solutions of the pure monovanadyl complex do not test for the presence of the oxalate ion. Complexes of sulfate and sulfite analogous to the oxalate complexes have been observed [4]. Ducret [5] suggested the existence of weak fluoro complexes at a pH of approximately 3. A tartrate and two citrate complexes can also be formed with the vanadyl ion. 

In addition to the oxide carboxylates, beryllium forms numerous chelating and bridged complexes with ligands such as the oxalate ion C204 , alkoxides, /9-diketonates and 1,3-diketonates. These almost invariably feature 4-coordinate Be... 

Calcium can be determined as the oxalate by precipitation from homogeneous solution by cation release from the EDTA complex in the presence of oxalate ion.28... 

C18-0121. Zinc forms an octahedral complex ion with three bidentate oxalate ions ... 

In acidic solution MnOj is usually the end product, although particularly vigorous reductants, e.g. iodide and oxalate ions, convert permanganate to manganous ions. Mn(III) is stable only in acidic solution or in the form of a complex, e.g. with pyrophosphate ion, and it has seldom been reported as the end product of a permanganate oxidation, e.g. for that of Mn(II) in a phosphate buffer and for those of alcohols and ethers in the presence of fluoride ion. ... 

Stability constants (ethylendiamine, glycinate, oxalate), surface complex formation constants and solubility products (sulfides) of transition ions. The surface complex formation constant is for the binding of metal ions to hydrous ferric oxide =Fe-OH + Me2+ =FeOMe++ H+ K. ... 

Fig. 4.18 Decrease in distribution ratio of Be(II) as a function of oxalate ion (Ox ) concentration due to formation of aqueous BeOXo complexes. The extraction system is 0.03 M TTA in methyUsobutylketone and 1.0 M Na(0.5 Ox T CIO)). See Eq. (4.72) for ordinate function. (From Ref. 31.)...

Desorption of the reduced metal ion is the rate determining step and is assisted by protons and oxalate ions. The reoxidized surface complex also desorbs owing to its altered molecular structure and is thus available for further reaction. The reductive dissolution step is faster than the initial complexation process. Photochemical dissolution of hematite in acidic oxalate solution is faster when air is excluded from the system (by purging with N2) than when air is present (Taxiarchou et al. 1997). 

Murmann (18) has investigated the reaction of some amineoximatonickel (II) complexes with EDTA as well as isotopic ligand exchange with the amineoximes. These systems are rather complicated, but the replacement rate of the chelate ligand does show the typical two term rate law (22). It was also observed that the reaction rate is catalyzed by the addition of other substances such as ammonia, ethylenediamine and oxalate ion. 

The designations a, /3, or y after some formulas refer to particular crystalline forms (which are customarily identified by Greek letters). Data for salts except oxalates are taken mainly from A. E. Martel and R. M. Smith, Critical Stability Constants. Vol. 4 (New York Plenum Press, 1976). Data for oxalates are from L. G. Sitlen and A. E. Martell, Stability Constants of Metal-Ion Complexes, Supplement No. 1 (London The Chemical Society, Special Publication No. 25,1971). Another source R. M. H. Verbeeck et al., Inorg. Chem. 1984, 23, 1922. 

Note that these compounds are not enantiomers, but true diastereomers with different properties, and they may be separated by fractional crystallization. The asymmetric carbon atom has an 5 configuration in both diastereomers, but the chirality about the molybdenum atom is different. Thus the asymmetric carbon aids in the resolution of the molybdenum center, but its presence is not necessary for the complex to be chiral. It is merely necessary for the Schiff base to be unsymmetric, i.e., have one pyridine nitrogen and one imino nitrogen. If the bkJentate ligand had been ethylenediamine, bipyridine, or the oxalate ion, there would have been a mirror plane and no duality at the molybdenum. 

A widely applicable masking agent is sodium triphosphate, Na5P3Oi0-6H2O, which readily complexes with a very wide variety of cations in all groups of the Periodic Table, preventing their precipitation by alkali hydroxide, ammonia, phosphate, carbonate or borate. It is used commercially as Calgon to mask calcium which cannot then form precipitates with citrate, fluoride or oxalate ions and in many other instances (see Table 3). 

Complexes containing unidentate coordination have depended for their characterization upon physicochemical methods rather than structural determinations. The monomeric octahedral co-balt(III) complex [Co(en)2X(ox)], where X = halogen or OH, provides one of the few examples of unidentate oxalate coordination the conformation was determined from IR data.65 By contrast, there are numerous examples of structurally characterized chelating dicarboxylate systems. There are several structural determinations of different forms of oxalic acid and its ions but the most useful for comparative purposes are those of a-oxalic acid and anhydrous sodium oxalate. Using the planar ( >2 ) oxalate ion and acid as benchmarks it can be seen (Table 4) that the rj4 oxalate ligand (bite = 265 pm)66 has two long and two short C—O bonds. The coordinated C—O(M) bond resembles the C—O bond of the acid while the free C=0 bonds are similar to those in the oxalate... 

Titanium(III) chloride in the presence of oxalate ions or complexed with other ligands such as EDTA, NTA, DTPA or HETA is a developer.40 The TiIH—DTPA developer maintains constant activity over a wide pH range (3—10), is relatively non-toxic and safe to handle, and has some desirable properties as a single-use developer.41... 

Principle of Separation. Uranium as the U02+ ion in strong chloride solutions forms an anionic chloride species such as U02C13 thorium does not. If a solution in which the chloride ion has been adjusted to form the uranyl chloride complex is passed through a cation exchange column, the uranium passes through the column and cationic Th+4 is absorbed. After the column is washed to insure that no uranium remains, the absorbed thorium is complexed with oxalate ions to form an anion and is released from the column. Although thorium generally is precipitated with oxalate ions, with excess quantities of oxalate it forms a soluble anionic species. The mass of thorium in this experiment is extremely low relative to that of oxalate and will not form a precipitate. 

A similar but, perhaps, more interesting case is that of the ion pairs between Co(sep)3+ and oxalate ions. Excitation of the ion pair in the IPCT band leads to the formation of the Co(II) complex and of an oxalate radical which undergoes a fast decomposition reaction. Thus, the back electron transfer reaction is prevented and Co(sep)2+, which is a good reductant, can accumulate in the system. When colloidal... 

It was found that oxalate ions, (C204)2-, are excellent ligands for rhenium in the +7 oxidation state. This simple dicarboxylic acid is able to form intermediate Re( VII) complexes that are sufficiently stable to allow the expansion of the coordination sphere, but also sufficiently substitution-labile to permit the re-... 

Fig. 20 Pictorial illustration of the hypothetical mechanism of the action of oxalate on the reduction of [188Re04]. Oxalate ions react first with the teraoxo anion forming an intermediate Re(VII) complex and causing the concomitant expansion of the coordination sphere of the metal from tetrahedral to octahedral. Successively, electron transfer takes place from Sn2+ ions to the octahedral metal center...

---