Fred Fairbrother

The oxytrichlorides and oxytribromides of niobium (columbium)(V) and tantalum(V)

Abstract A number of methods of formation of niobium and tantalum oxytrichlorides and oxytribromides have been investigated. NbOCl3, NbOBr3 and TaOBr3 have all been obtained in a crystalline condition by the action of molecular oxygen on the heated pentahalide. Tantalum oxytrichloride, which is thermally the least stable of these compounds has been obtained, in a non-crystalline condition, by pyrolysis of the pentachloride—diethyl ether complex. Niobium oxytrichloride and oxytribromide can be sublimed in a vacuum without decomposition: the tantalum compounds cannot. All four oxytrihalides undergo decomposition into pentahalide and pentoxide on heating, the niobium compounds being more stable in this respect than the tantalum. The vapour pressure of niobium oxytrichloride has been measured up to a temperature (~ 340°C) at which thermal decomposition affects the results.

The reactions of niobium and tantalum pentachlorides and pentabromides with some sulphoxides

Abstract The reactions of dimethyl sulphoxide and diphenyl sulphoxide with niobium and tantalum pcntachlorides and pentabromides have been investigated. The reactions involve abstraction of the oxygen atom of the sulphoxide group by the metal atom, to form the corresponding oxyhalide and halogen substituted sulphides, together with co-ordination of further molecules of the sulphoxide to the oxyhalide. The oxyhalide-sulphoxide adducts have been isolated and characterised by analysis, m.p. and a study of their infra-red spectra.

THE REACTIONS OF NIOBIUM AND TANTALUM PENTACHLORIDES WITH TRIPHENYLPHOSPHINE AND TRIPHENYLARSINE OXIDES

Abstract The reactions of niobium and tantalum pentachlorides with excess of triphenylphosphine oxide, triphenylarsine oxide or their hydrogen peroxide adducts, are similar to the reactions of these pentahalides with sulphoxides, in that they involve abstraction of oxygen from the oxides, to form metal oxytrichlorides to which are co-ordinated additional molecules of the undecomposed ligand. The co-products of the reactions are dichlorotriphenylphosphine and dichlorotriphenylarsine respectively. When the triphenylphosphine hydrogen peroxide adduct is used as a reactant however, the dichlorotriphenylphosphine is quantitatively oxidised with liberation of chlorine gas; by contrast, dichlorotriphenylarsine is not oxidised and can be isolated from the reaction with the triphenylarsine hydrogen peroxide adduct. Tantalum pentabromide undergoes a similar reaction with triphenylarsine oxide, the dibromotriphenylarsine being unoxidised by the hydrogen peroxide adduct. No corresponding abstraction of sulphur from triphenylphosphine sulphide by niobium pentachloride appears to occur, preliminary experiments indicating the formation of a 1:1 complex.

Complex compounds of indium trihalides part I. Ether complexes

Abstract Complex compound formation between indium trichloride, tribromide and triiodide, and a number of ethers has been examined. Twenty-three systems were examined and in all but three complex formation was observed, twentyfive definite compounds being identified. An outstanding feature was the widespread formation of 1 : 2 complexes, in contrast to the behaviour of the trihalides of other members of this group, which form predominantly 1 : 1 complexes. In all cases indium trichloride dissolves in an ether very slowly, even when the ultimate solubility is high. This is correlated with an energy of re-organization of the ionic solid to form a molecular complex. Stereochemical considerations affect the complexing powers of the different ethers.

The reactions of dimethylsulphoxide with niobium and tantalum pentafluorides

Abstract Dimethylsulphoxide reacts with niobium and tantalum pentafluorides to form the stable 1:2 adducts NbF 5 ,2(CH 3 ) 2 SO and TaF 5 ,2(CH 3 ) 2 SO. The densities, viscosities and electrical conductivities of these complexes in the molten state have been measured over a range of temperatures. The results indicate a high degree of molecular complexity and also of self-dissociation in the liquids.

Some water-soluble complexes of pentavalent niobium and tantalum

Abstract One of the characteristic properties of these elements, and which impressed their discoverers, is the insolubility of their oxides in all common reagents. For long after their discovery the only known water-soluble compounds were the complex fluorides, which are still used for their separation. It has been known however for a long time that the hydrated oxides will dissolve in aqueous solutions of oxalic, tartaric and citric acids and in alkaline solutions of catechol and pyrogallol. We have now recently shown that water-soluble complexes can also be formed with a variety of other α-hydroxy acids, which may be phenolic or carboxylic, and with a number of amines. Complex formation with hydroxy compounds occurs through a condensation mechanism, akin to the flocculation or ageing of the hydroxides, in which small units are attached to the complexing agent by elimination of water. Amine complex formation appears to occur through co-ordination by a usual type of donor-acceptor mechanism and is affected by steric considerations and may be correlated with the basic dissociation constant of the amine. One outstanding feature of the dissolution in solutions of these complexing agents is the much greater solubility of pure niobic acid as compared with pure tantalic acid. When the two oxides are co-precipitated however, part of the tantalum may be carried into solution with the niobium. This is a consequence of the polynuclear character of the complexes.

COMPLEXES OF NIOBIUM AND TANTALUM HYDROXIDES WITH DI-OLS

Abstract The dissolution of niobium and tantalum hydroxides in alkaline solutions of catechol and other 1–2,di-ols has been studied and solid crystalline products isolated. These show some variability in composition consequent upon the polynucleation of the metal hydroxide through ageing. Under appropriate conditions such compounds as (NH4)3[Nb(OH)2(C6H4O2)3].H2O may be isolated. This compound absorbs at 340 mμ in ethanol but is immediately hydrolysed in water or aqueous alkali and subsequently, within certain limits of OH- concentration, a species absorbing at 310 mμ — probably a 1: 1 complex and containing polynuclear niobic acid units — is slowly formed. Infra-red absorption measurements give no evidence of the presence of a niobyl radicle, NbO, in the solids. Tantalum hydroxide is much less easily dissolved in catechol than niobium hydroxide and the products contain about 5 moles of catechol to each tantalum atom.

The solubilities of niobium and tantalum pentachlorides in some hydrocarbons and carbon tetrachloride

Abstract The solubilities of tantalum pentachloride in cyclohexane, benzene, toluene, m -xylene, mesitylene and carbon tetrachloride, and of niobium pentachloride in benzene have been measured.