Niobium Ferrocyanides

As might be anticipated from its very weakly acid nature, niobium pentoxide does not give rise to any cyanides. By the action of hydrochloric acid and potassium ferrocyanide on solutions of niobic acid, three brown powders have been obtained. The following are some of the formulae that have been allotted to them: KNb[Fe(CN)₆]₂; K₂Nb₁₂[Fe(CN)₆]; K₉(NbO)₅.[Fe(CN)₆]₆.10H₂O; but the evidence for these is weak.