The new alkoxides Nb(OR),, where R = Me, Et, Prn, Bun, or n-pentyl, have been prepared by reactions involving niobium pentachloride, the alcohol, and ammonia, or by alcohol-interchange involving niobium pentaethoxide. Boiling points under reduced pressure and ebullioscopic molecular weights in benzene, in toluene, and in the parent alcohols were determined. The niobium n-alkoxides are less stable than the corresponding tantalum compounds. The volatilities and molecular complexities of the niobium and tantalum n-alkoxides are discussed from the theoretical viewpoint.THE preparation and properties of some tantalum penta-n-alkoxides have recently been described.l In view of the chemical similarity between niobium and tantalum it seemed worthwhile to investigate the alkoxides of niobium. Additional interest was centred on the relative volatilities of corresponding niobium and tantalum alkoxides because of the possibility that the effect of molecular weight on volatility might be apparent. This communication deals with the rt-alkoxides Nb(OR),, where R = Me, Et, Prn, Bun, and ut-pentyl.These compounds may be prepared by either of the methods :Niobium pentamethoxide is a white crystalline solid, m. p. 60" [cf. Ta(OMe),, m. p. 50"], but the other rt-alkoxides are pale yellow liquids. The ease of hydrolysis in water appears to parallel the water-miscibility of the parent alcohols. A notable feature of the niobium rt-alkoxides is the decrease in thermal stability with increase in length of the alkyl chain in contrast to the behaviour of the corresponding n-alkoxides of tantalum. Thus distillation of niobium ut-pentyloxide causes decomposition even at 0.1 mm. whereas tantalum rt-pentyloxide boils unchanged at a higher temperature. The boiling points of niobium and tantalum rt-alkoxides under reduced pressure are presented in the Table : their main

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