• N R Srinivasan

Articles written in Proceedings – Section A

• Studies on niobium and tantalum - Part I. Tartratoniobic acid

The formation of a higher order compound of niobium with tartaric acid has been investigated. Freshly precipitated niobic acid reacts with tartaric acid to yield a definite complex compound. The conditions of its formation have been studied. It analyses to the composition Nb2O5· (C4H4O5)2·10H2O. It is a light straw coloured substance and is very soluble in water. Its properties have been investigated. Its electrical eonductivity has been determined at a series of dilutions and its basicity has been determined by the Ostwald method. Molecular weight of the compound has been found out by the cryoscopic method. The optical rotation of its solution shows an enhanced rotation. Dehydration conducted in air and in vacuum has revealed some features regarding its structure. According to the Rosenheim-Miolati theory, it is formulated as a heteropoly acid being derived from metaniobic acid H7NbO6 by the repacement of oxygen atoms by a tartrate radical and is represented as$$H_5 \left[ {Nb\begin{array}{*{20}c} {O_4 } \\ {\left( {C_4 H_4 O_6 } \right)} \\ \end{array} } \right]2 \cdot 5 H_2 O$$.

It is named as 2-tartrato-2-niobic acid 10-hydrate.

• Studies on niobium and tantalum - Part II. Alkali tartratoniobates

This paper details the work on a new class of compounds called the tartratoniobate. In an intensive investigation on the alkali niobates, some earlier data on the lithium niobates have been contradicted. Two new niobates 2viz., 3 K2O.4Nb2O5. 20 H2O and 4 Li2O.3 Nb2O5.15 H2O have been isolated. The reaction of tartaric acid on several niobates of lithium sodium and potassium has been studied in detail and has resulted in the following tartratoniobates; Li2O.Nb2O5.(C4H4O5)2.8 H2O Na2O.Nb2O5. (C4H4O5)2.nH2O and K2O.Nb2O5.(C4H4O5)2.n H2O (n=6 or 10). The properties of each of these compounds have been studied in detail and the difficulty in crystallisation and anomalous solubility have been adequately explained. Dehydration has been conducted in air and in vacuum. A heteropoly acid structure has been assigned to the tartratoniobates.

• Studies on niobium and tantalum - Part III. Tartratoniobates of alkaline earth and other metals

The niobates of the alkaline earth and other metals are insoluble and hence the tartratoniobates of these metals are prepared by double decomposition of soluble metal salts with potassium tartratoniobate. The calcium-2-tartrato-2-niobate 10-hydrate of the formula CaO·Nb2O5·(C4H4O5)2·10 H2O has been prepared and studied. The strontium tartratoniobate prepared has the formula SrO·Nb2O5·(C4H4O5)2·10 H2O. A copper compound of the formula CuO·Nb2O5·(C4H4O5)2·10 H2O has been prepared in a similar manner.

The barium and lead tartratoniobate are also prepared by the above method of double decomposition but they are obtained as basic salts of the formulæ 4 BaO·3Nb2O5·(C4H4O5)6·16 H2O and 5 Pb·O·3Nb2O5·(C4H4O5)6·20 H2O. It is significant that the dehydration of the barium salt gives a practically anhydrous compound. The calcium, strontium and copper compounds obtained are considered as the normal salts of the 2-tartrato-2-niobic acid whereas those of barium and lead are regarded as basic salts. Suitable heteropoly acid structures are assigned to these compounds.

• Studies on niobium and tantalum - Part IV. Polynuclear complexes

It has been found that in aqueous solutions, on vigorous boiling, the 2-tartrato-2-niobates and the corresponding free acid are degraded, giving rise to new complexes of niobium. The conditions of formation and the mechanism of the reaction have been studied. Adequate explanation has been offered for the phenomenon. The compounds are regarded as polynuclear complexes and suitable structures are given for the compounds prepared.

• Studies on niobium and tantalum - Part V. Tartratotantalates

It has been shown that literature does not reveal the existence of any complex compound of tantalum with tartaric acid. Experiments conducted yielded tartratocomplexes with sodium and potassium tantalates. The complexes have been analysed and their properties found to be similar to those of the tartratoniobates. The mode of formation of these compounds has been explained. They are formulated with heteropoly acid structures of the general type$$M H_4 \left[ \begin{array}{l} O_4 \\ Ta \\ (C_4 H_5 O_6 \\ \end{array} \right] n H_2 O$$ where M Na or K and n a varying number.

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