Some water-soluble complexes of pentavalent niobium and tantalum

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