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.