Complex metal-oxalate

Many different types of complex metal oxalates have been described, the best known being the trioxalato salts of the... 

Despite the volume of work concerned with metal-catalyzed decomposition of diazo compounds and carbenoid reactions 28>, relatively little work has been reported on the metal-catalyzed decomposition of sulphonyl azides. Some metal-aryl nitrene complexes have recently been isolated 29 31>. Nitro compounds have also been reduced to nitrene metal complexes with transition metal oxalates 32K... 

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

Catalytic decarboxylation processes occur in aliphatic keto acids in which the keto group is in an a-position to one carboxyl group and in a P-relationship to another. Thus, the normal decarboxylation of a p-keto acid is facilitated by metal coordination to the a-keto acid moiety. The most-studied example is oxaloacetic acid and it has been shown that its decarboxylation is catalyzed by many metals following the general order Ca2+ < Mn2+ < Co2+ < Zn2+ < Ni2+ < Cu2+ < Fe3+ < Al3"1".66 67 The overall rate constants can be correlated with the stability constants of 1 1 complexes of oxalic acid rather than oxaloacetic acid, as the uncoordinated carboxylate anion is essential for the decarboxylation. The generally accepted mechanism is shown in Scheme 15. Catalysis can be increased by the introduction of x-bonding ligands, which not only increase the... 

Weinland, R. et al., Z. Anorg. Chem., 1929, 178, 219 The salt, probably complex, decomposes at 100°C. See other METAL OXALATES... 

Metal cyanides(and cyano complexes), 216 Metal derivatives of organofluorine compounds, 217 IV-Metal derivatives, 218 Metal dusts, 220 Metal fires, 222 Metal fulminates, 222 Metal halides, 222 Metal—halocarbon incidents, 225 Metal halogenates, 226 Metal hydrazides, 226 Metal hydrides, 226 Metal hypochlorites, 228 Metallurgical sample preparation, 228 Metal nitrates, 229 Metal nitrites, 231 Metal nitrophenoxides, 232 Metal non-metallides, 232 Metal oxalates, 233 Metal oxides, 234 Metal oxohalogenates, 236 Metal oxometallates, 236 Metal oxonon-metallates, 237 Metal perchlorates, 238 Metal peroxides, 239 Metal peroxomolybdates, 240 Metal phosphinates, 240 Metal phosphorus trisulfides, 240 Metal picramates, 241 Metal pnictides, 241 Metal polyhalohalogenates, 241 Metal pyruvate nitrophenylhydrazones, 241 Metals, 242 Metal salicylates, 243 Metal salts, 243 Metal sulfates, 244 Metal sulfides, 244 Metal thiocyanates, 246 Metathesis reactions, 246 Microwave oven heating, 246 Mild steel, 247 Milk powder, 248... 

After providing a brief description of zeolitic structures, we discuss the hierarchy of structures of open-framework metal phosphates ranging from zerodimensional monomeric units and one-dimensional linear chains to complex three-dimensional structures. Aspects related to the likely pathways involved in the assemblage of these fascinating structures are examined, pointing out how the formation of the complex three-dimensional structures of open-framework metal phosphates involves the transformation and assembly of smaller units. Besides the role of the four-membered monomer, the amine phosphate route to the formation of the three-dimensional structures is discussed. The last step in the formation of these structures from preformed units of the desired structure is likely to be spontaneous. Our recent studies of open-framework metal oxalates have shown the presence of a hierarchy of structures. Reactions of amine oxalates with metal ions yield members of the oxalate family with differing complexity. 

Metal ascorbates are frequently associated with redox chemistry, particularly when the metal is redox active, which includes most transition metal ions . The redox activity of AA also leads to decomposition of its Co(II) and Gd(III) complexes into oxalate complexes . AA is considered a major reductant for Cr(IV) to yield Cr(III) °. Reduction of CrOs with excess of AA affords a Cr(III)-ascorbate complex. However, the structure of this complex was not determined. Since Cr(III) has been demonstrated to play a role in glucose metabolism, it is thus important to investigate further the reduction of high-valent Cr species by AA and binding of AA to Cr(III). 

Larger organic molecules can form complexes with metal ions, too. Radiator cleaner consists of a water-soluble complexing agent, such as the organic compound oxalic acid, which forms a water-soluble cage around metal ions and lifts them from the walls of the radiator. The metals that are found deposited on radiator walls, such as calcium, were once dissolved in the radiator water. We don t normally think of calcium as being a metal, but it is. Calcium is located on the left side of the periodic table, which makes it a metal, and it can form coordination complexes as transition metal ions do. When calcium forms a complex with oxalic acid, the calcium becomes water soluble. 

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). 

Few data are available on the concentration of dicarboxylic acid anions in subsurface waters. C2 through C q saturated acid anions have been reported in addition to maleic acid (cz5-butenedioic acid) (5. 15-16L Oxalic acid (ethanedioic) and malonic acid (propanedioic) appear to be the most abundant. Reported concentrations range widely from 0 to 2540 mg/1 but mostly are less than a few 100 mg/1. Concentrations of these species in formation waters are probably limited by several factors, including the very low solubility of calcium oxalate and calcium malonate (5), and the susceptibility of these dicarboxylic acid anions to thermal decomposition (16). This paper will focus on the monocarboxylic acids because they are much more abundant and widespread, and stability constants for their complexes with metals are better known. We do recognize that dicarboxylic acid anions may be locally important, especially for complexing metals. 

Thermogravimetric curves for solid K2[Pd(C204)2],3H20 and other transition-metal oxalates indicate that the thermal stability of the anhydrous complexes decreases with increase in electron affinity of the central metal ion. AH values were obtained for both dehydration and decomposition. Subsequent studies showed carbon dioxide as the only gaseous product, the decomposition occurring via electron transfer from a 304 ligand to the central palladium. ... 

Calcination of the oxalate coprecipitates readily yielded phase-pure perovskite-type complex metal oxides. The required calcinations for the microemulsion-derived mixed oxalates were 100-250"C below the temperatures used for oxalates prepared in homogeneous aqueous solutions. 

Silicate is determined spectrophotometrically with ammonium molybdate and ammonium vanadate. The pH of the sample must be adjusted to 7-8. Potassium cyanide is added to prevent interference of heavy metals. Oxalic acid is added to destroy mo-lybdophosphate and vanadophosphate and to bind aluminum in a complex. As in all spectrophotometric determinations, high and variable optical absorption of the sample (due to color or turbidity) at the wavelengths of investigation causes errors tannin, iron, and sulfide also interfere. To avoid contamination, all contact surfaces should be of polyethene. It is also possible to determine silicate using FAAS, in which case nitrous acid and ethyne must be used as flame gases. As silicates are present in colloidal form, the sample must be introduced into the AAS equipment using an ultrasonic nebulizer. Such a nebulizer is also used when silicate is measured by ICP-AES. 

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