Complex oxalates

instead of triphenylphosphine, a disubstituted alkyne C2R2 is added to the photolytic reaction, the product is the alkyne zerovalent complex Pt(C2R2)(PPh3)2  

Pt(C204)(PPh3)2 + C2R2 Pt(C2R2)(PPh3)2 + 2C02 

If Pt(C204)(PPh3)2 is photolyzed in the presence of chloroform or a monosubsti-tuted alkyne PhC=CH, the respective compounds cij-PtCl2(PPh3)2 and trans-Pt(C =CPh)2(PPh3)2 are now formed  

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The simplest dicarboxylate ligand is oxalate, 020 . Thorium oxalate complexes have been used to produce high density fuel pellets, which improve nuclear fuel processes (73). The stabiUty of oxalate complexes and the relevance to waste disposal have also been studied (74). Many thorium oxalate complexes are known, ranging from the simple Th(C20 2 >5rl2 complex salts such as where n = 4, 5, or 6 and where the counterions... 

This is an typical example of a dicarboxylic acid in that C-C cleavage is the only route for oxidation. No study of the Co(III) oxidation has been made although it is highly probable that reaction would proceed through an oxalate complex. The thermal decomposition of Co(Ox)3 has been shown to be a first-order process and probably involves an internal redox reaction, viz. 

A PRP -1 (Hamilton Reno, NV) reversed phase column was coated with cetylpyridinium and eluted with tetramethylammonium salicylate acetoni-trile water.89 The separation was comparable to that observed on conventional ion exchange. Coated phases were also used to separate oxalate complexes of manganese, cobalt, copper, and zinc.90 Reversed phase silica supports were coated with poly(N-ethyl-4-vinylpyridinium bromide), poly(dimethydiallylammonium chloride), poly(hexamethyleneguanidinium... 

Janos, P., Separation of some metals as their anionic oxalate complexes by reversed-phase ion-interaction chromatography, /. Chromatogr., 635, 257,1993. 

If a chemical reaction regenerates the initial substance completely or partially from the products of the electrode reaction, such case is termed a chemical reaction parallel to the electrode reaction (see Eq. 5.6.1, case c). An example of this process is the catalytic reduction of hydroxylamine in the presence of the oxalate complex of TiIV, found by A. Blazek and J. Koryta. At the electrode, the complex of tetravalent titanium is reduced to the complex of trivalent titanium, which is oxidized by the hydroxylamine during diffusion from the electrode, regenerating tetravalent titanium, which is again reduced. The electrode process obeys the equations... 

The NH2 radical rapidly reacts with excess oxalic acid required to form the oxalate complexes of titanium. 

The reaction of platinum(IV) complexes with ascorbate results in very slow reduction and for [PtCl2(OH)2(A ,A -dmen)], in the formation of the oxalate complex [Pt(C204)Cl(0H)(A , A-dmen)].508... 

Table XIX contains stability constants for complexes of Ca2+ and of several other M2+ ions with a selection of phosphonate and nucleotide ligands (681,687-695). There is considerably more published information, especially on ATP (and, to a lesser extent, ADP and AMP) complexes at various pHs, ionic strengths, and temperatures (229,696,697), and on phosphonates (688) and bisphosphonates (688,698). The metal-ion binding properties of cytidine have been considered in detail in relation to stability constant determinations for its Ca2+ complex and complexes of seven other M2+ cations (232), and for ternary M21 -cytidine-amino acid and -oxalate complexes (699). Stability constant data for Ca2+ complexes of the nucleosides cytidine and uridine, the nucleoside bases adenine, cytosine, uracil, and thymine, and the 5 -monophosphates of adenosine, cytidine, thymidine, and uridine, have been listed along with values for analogous complexes of a wide range of other metal ions (700). Unfortunately comparisons are sometimes precluded by significant differences in experimental conditions.

An NMR investigation of water exchange at [Pt(H20)2(oxalate)2] is relevant to the mechanism of formation of one-dimensional mixed valence oxalatoplatinum polymers. In fact the rate constant for this presumably dissociative (AS = + 42 JK mol-1) reaction is considerably too low for water loss to be, as recently proposed, the first step in formation of these polymers. The mechanism of trans to cis isomerization for this oxalate complex, and for its (2 -methyl)malonate analogues, is intramolecular (Bailar or Ray-Dutt twist), since there is no concurrent incorporation of labeled solvent (177). 

Figure 6.27 Square-wave voltanunogram obtained for the electro-reduction of a ferric oxalate complex (5 x 10 mol dm ) in aqueous oxalate buffer r = 33.3 ms, sw = 30 mV and A = 5 mV. Reprinted with permission from Turner, J. A., Christie, J. H., Vukovic, M. and Osteryoung, R. A., Anal. Chem., 49, 1899-1903 (1977). Copyright (1977) American Chemical Society.

Other first-row transition metal oxalate complexes behave similarly." ... 

Example 10 Determination of formation constants for Be(II) oxalate complexes. 

The advantage of this strange ordinate is that the curvature only reflects the oxalate complexation. 

Kinetics and mechanisms of complex formation have been reviewed, with particular attention to the inherent Fe +aq + L vs. FeOH +aq + HL proton ambiguity. Table 11 contains a selection of rate constants and activation volumes for complex formation reactions from Fe " "aq and from FeOH +aq, illustrating the mechanistic difference between 4 for the former and 4 for the latter. Further kinetic details and discussion may be obtained from earlier publications and from those on reaction with azide, with cysteine, " with octane-and nonane-2,4-diones, with 2-acetylcyclopentanone, with fulvic acid, and with acethydroxamate and with desferrioxamine. For the last two systems the various component forward and reverse reactions were studied, with values given for k and K A/7 and A5, A/7° and A5 ° AF and AF°. Activation volumes are reported and consequences of the proton ambiguity discussed in relation to the reaction with azide. For the reactions of FeOH " aq with the salicylate and oxalate complexes d5-[Co(en)2(NH3)(sal)] ", [Co(tetraen)(sal)] " (tetraen = tetraethylenepentamine), and [Co(NH3)5(C204H)] both formation and dissociation are retarded in anionic micelles. 

These solid phases are connected to the components in Fig. 4, with which they are in reversible equilibrium. For example, if magnesium ion were added to a complex solution containing solid calcium oxalate monohydrate (COM), the magnesium would compete with calcium for an increased share of the oxalate this would reduce the amount of the calcium oxalate complex, and finally a small amount of calcium oxalate sohd would dissolve to restore the complex concentration to its equilibrium value. In urine, this picture must be extended to account for the molecular substances that coat crystals and reduce access of the solution to the surface coated crystals do not redissolve readily. 

The Fe -oxalate complex then adsorbs on goethite (step 2) where it exchanges an electron with a surface Fe atom to form Fe (step 3) and is itself reoxidized. 

Based on measurements of iron in both the (II) and (III) oxidation states and the anions in cloudwater and fogwater, Siefert et al. (1998) calculate that most of the Fe(III) is in the form of hydroxy species such as Fe(OH)2, with much smaller amounts (<10%) in the form of oxalate complexes such as Fefoxalate),. ... 

A classical case in the field of oxidation of organic ligands is the decomposition of the manganic oxalate complexes (31,84,85)... 

Arthur Adamson Actually, Dr. Harris is the better man to make this particular remark, I suspect. In the case of oxalate complexes it seems necessary to assume an ortho or hydrated formulation of one end of an oxalate as it detaches from the coordination sphere in order to explain the O18 exchange. This is not exactly what you are talking about, but it is an illustration of one instance where ortho acid formation seems desirable. 

Stuart R (2002) Insertion of proteins into the inner membrane of mitochondria the role of the Oxal complex. Biochim Biophys Acta 1592 79-87 Stuart RA, Cyr DM, Craig EA, Neupert W (1994) Mitochondrial molecular chaperones their role in protein translocation. Trends Biochem Sci 19 87-92 Sutak R et al. (2004) Mitochondrial-type assembly of FeS centers in the hydrogenosomes of the amitochondriate eukaryote Trichomonas vaginalis. Proc Natl Acad Sci USA 101 10368-10373... 

The crystal structure and absolute configuration of l-( - )-[Cr(acac)3] has been reported.772 The circular dichroism of D-[Cr(acac)3] has been studied in the solid state and in solution.773 The rotational strengths of the d-d transitions are extensively discussed competing rather than reinforcing effects lead to the smaller rotational strengths observed for tris(acetylacetonates) as compared to tris-(ethylenediamine) or -oxalate complexes. 

Oxalate complexes of chromium(III) were first characterized at the turn of the century by Rosenheim and Cohen.877 The most extensively studied are the tris species and the cis- and frarw-bisoxalates (205-207) these formulations were first suggested by Werner.878 All may be made by the reduction of chromate with oxalate. Reliable preparations have been reported for tris by Kauffman and Faoro879 and for cis- and rrans-diaquabisoxalatochromateflll) by Bailar.880... 

Table 4 Bond Distances and Angles for ij4 Oxalate Complexes...

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