Complexes of molybdenum and tungsten in aqueous solution

McCallum, James D. P (1966) Complexes of molybdenum and tungsten in aqueous solution. PhD thesis, University of Glasgow.

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A series of complexes has been prepared in aqueous solution between sodium molybdate (and sodium tungstate) and the organic ligands: D(+) tartaric, L(-)mandelic, oxalic, trans-aconitic and itaconic acids, the disodium salt of 1,2-dihydroxy-benzene-3,5-disulphonic acid (tiron). D(+) mannose, D(-)ribose and L(-)sorbose, D-mannitoll and D-sorbitol, and hydroxylamine. Two different types of complex were obtained, one with one ligand and the other with two ligands coordinated to the molybdate or tungstate ion. All the complexes are strongly pH dependent in their formation, the pH range for complexing generally being between pH = 4.5 and 7.0, but with the polyhydroxy alcohols complexing can be obtained down to pH = 2.0. For pH values greater than 7.5 decomposition of the complexes into their constituents takes place, while for values of pH below 4.5 the molybdate and tungstate ion tend to polymerize. This latter fact suggests that the 2:1 metal: ligand ratio of polyhydroxy alcohol complexes may arise from the molybdate and tungstate ion being dimerized, since these complexes, as indicated above, at formed at a pH of 2.0. The methods used to determine the stoichiometry of the complexes were optical density and optical rotation measurements. The effects of light and heat on the complexes were observed by firstly irradiating the compounds with ultraviolet light and secondly refluxing them for several days. Although some of the complexes were unaffected (e.g. those of glycolic and citric acids) or were reduced to molybdenum blue (D-mannitol and D-sorbitol), others formed deep red coloured solutions which contained molybdenum (V) (D(+)tartaric acid, L(-)mandalic acid, D(+)mannose, D(-)ribose and L(-)sorbose), a redox mechanism operating between molybdate and the ligand. In the case of the mandelic acid complex an orange solid of composition NaMoO3.2H2O was obtained, with benzaldehyde as the oxidation product of the mandelic acid. The effects of various ions such as sulphate, carbonate, phosphate, nitrate and nitrite upon the refluxing solutions was also examined. It was found that sulphate, phosphate and carbonate ions inhibited the reduction in different ways. The effect of nitrate and nitrite ions depended on the nature of the ligand - sugar complexes were unaffected, the reduction of molybdate by mandelic acid was decreased and the tartrate complex was stabilized as the colourless molybdenum (VI) compound.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: D H Brown
Keywords: Inorganic chemistry
Date of Award: 1966
Depositing User: Enlighten Team
Unique ID: glathesis:1966-73387
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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