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Addition of NaMoO to an excess of aspartic acid (AspH) can produce any of four different complexes depending on the pH, namely [MoO(Asp)], [MoO(Asp)], [MoO(OH)(Asp)] and [MoO(Asp)]. The ranges of formation of these species with pH, the number of equivalents of acid necessary for their formation, and their stoichiometries, condensation degrees and stability constants, have been calculated by potentiometric and spectrophotometric techniques. The aspartic acid acts as a tridentate ligand in all cases. [ABSTRACT FROM AUTHOR]

Tungsten(VI)-citrate complexes, which occur in aqueous solution, were studied by polarimetric and absorbance measurements. The pH of the medium is the principal variable controlling complex formation and interconversion equilibria. At high pH (>6), the stable complexes are monomers with 1∶2 and 1∶1 stoichiometry, depending on the tungsten(VI)-citrate ratio, while at lower pH two different dinuclear complexes are formed. The intervals of existence of these species with the pH, the number of equivalents of acid necessary for their formation, as well as the conditional stability constant, have also been calculated. The structure of these compounds have been investigated byH andC-n.m.r. spectroscopy. The n.m.r. results indicate the existence in all these species of strong, covalent metal-toligand oxygen bonding via the carboxylic oxygen atom and the adjacent hydroxylic oxygen. [ABSTRACT FROM AUTHOR]

A polarimetric study of the tungsten (VI)-gluconic acid system in an excess of metal reveals the formation of four stable complexes: two monomers with 1 : 2 and 2: 1 stoichiometries and two dimers of 2:2 composition. The pH ranges of these species, the amount of acid equivalents their formation requires, and their conditional stability constants have also been calculated. The probable coordination of the organic ligand to the metallic centre in solutions containing different metal : ligand ratios has been investigated byC-n.m.r. spectroscopy. The results confirm the formation of different complexes depending on the reagent which is in excess. The behaviour of the system when the metal is in excess is related to that of other polyhydroxylic ligands such as mannitol and sorbitol. [ABSTRACT FROM AUTHOR]

Spectrophotometric and cryoscopic studies of the molybdenum(VI)-lactic acid (COH) system show the existence of three different oxoanion complexes in aqueous solution which have been isolated as [Co(en)] salts. These are one molybdodilactate {[MoO(COH]} and two dinuclear 1/1 species: [MoO(COH)(HO)] and [MoO(OH)-(COH)]. The pH of the medium is the main variable, controlling the formation equilibria which are similar to those previously described for other α-hydroxy-acid ligands. [ABSTRACT FROM AUTHOR]

Malonic acid (COH) and Mo form in aqueous solution two dinuclear dioxo-complexes of which the stability is a function of the pH of the medium. Both complexes have a 1∶1 metal-ligand stoichiometric ratio, and the interconversion may involve a structural rearrangement. Conditional dissociation constants have been determined spectrophotometrically. Saline cryoscopy supports the spectrophotometric results. Salts of [Co(en)] have been isolated. The ligand behaviour of malonic acid differs partially from that observed for α-polyhydroxy ligands. [ABSTRACT FROM AUTHOR]

The polarimetric study of the W-sorbitol system shows the formation of three stable complexes. The species stable at higher pH is monomeric ([WO(OH)(CHO)]), while the other two are dinuclear complexes of different stoichiometries ([WO(OH)(CHO)] and [WO(OH)(CHO)]). The interconversion equilibria have been established and the formation constants determined. The behaviour of sorbitol is like that displayed by other polyhydroxylic ligands having one or two carboxylic groups. The substitution of a carboxylic group for an alcoholic one seems only to result in lower stability constants for the complexes formed. [ABSTRACT FROM AUTHOR]