Oxalate, ligand property

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.

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. 

Dicarboxylic acids form monomeric complexes with palladium(II), K2[Pd(X2)2] (X2 = oxalate, malonate, etc,).153154 They may be prepared by warming a suspension of palladium(II) chloride with a concentrated solution of the alkali metal dicarboxylate or by using other palladium complexes containing readily substituted ligands such as [Pd(OH)2], [Pd(N03)2(H20)2] or [Pd(02CMe)2]3-155 These complexes are claimed to have useful antitumour properties.155 Complexes [Pd(X2)L2] (X2 = dicarboxylate L = amine or L2 = diamine) may be prepared by reaction of the dichloro complex with a carboxylate salt.156,128... 

There are two principal synthetic routes to dicarboxylate complexes. One of these uses an aqueous solution of the alkali metal dicarboxylate and the corresponding metal halide,93 while the other depends upon the dicarboxylic acid reduction of higher oxidation state metals. This reductive property of oxalic acid results in its ready dissolution of iron oxides and hence a cleaning utility in nuclear power plants.94 Mention must also be made of the successful ligand exchange synthesis of molybdenum dicarboxylates, Mo(dicarboxylate)2 H2 O, from the corresponding acetate complex. Unfortunately the polymeric, amorphous and insoluble nature of these complexes has restricted the study of these systems, which may well provide examples of multiple M—M bonding in dicarboxylate coordination chemistry.95... 

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... 

Infrared and UV/vis data have been used by several authors to identify the C=C, C=0, and M—O stretches in the complexes synthesized 15, 18-21, 37, 38, 41, 44, 50, 54, 56, 58, 59, 64-66, 69, 74, 78, 80, 82, 103). Except in the initial research on first-row transition metal complexes of squaric acid, where these data were used in proposing structures, IR and UV/vis analysis have been used as supporting evidence for the particular coordination mode of the ligand 19,21,22, 45, 52, 59, 65). Infrared spectroscopy has also been utilized in the study of mixed oxalate/squarate complexes 118), although not to the same extent as in complexes of the oxalate ion. For example, Scott et al. studied the IR properties of Co(III) oxalate complexes with the hgand in a variety of chelating/bridging situations 119). 

Syntheses, Structures, and Properties of Molecular >. Si-Silicates Containing Bidentate l,2-Diolato(2-) Ligands Derived from a-Hydroxycarboxylic Acids, Acetohydroximic Acid, and Oxalic Acid ... 

Comparison plots such as these are a valuable predictive tool. Such plots are most useful when the cations or ligands chosen for comparison have similar properties, such as equal valence, similar size and geometry, and similar electron configurations and bonding properties. In this way, trends or differences in their plotted behavior can be more rationally understood. For example. Figure 6 compares the stability constants of oxalate and carbonate complexes with the same divalent cations. The equation of the line is log q = 1.11 log o- The plot... 

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