Niobium(V) oxalate is the hydrogen oxalate salt of niobium(V). The neutral salt has not been prepared.A Textbook of Inorganic Chemistry. Vol VI, Part III. Vanadium, Niobium and Tantalum. Charles Griffin & Company Ltd, 1929. pp 166. Oxalo-niobic Acid.
Complexes Niobium(V) can form complexes with hydroxy acids, as well as oxalic acid. The salt formed is more complex than tartaric acid for niobium (as opposed to tantalum).Shen, Panwen; et al. Series of Inorganic Chemistry. Vol 8. Titanium group, vanadium group, chromium group. Science Press, 2011. pp 279-280. NH4[NbO(C2O4)2(H2O)2]·3H2O starts to lose water at 125°C, and at 630°C, it fully decomposes, forming a compound known as niobium pentoxide;Xu, Xiaoshu; Su, Tingting; Jiang, Heng. Study on thermal decomposition process of niobium oxalate. Fenxi Yiqi, 2009. (5): 75-77. Heating this complex and sodium citrate at 650°C can form sodium niobate (NaNbO3).Bian, Yu-bo; Jiang, Heng; Su, Ting-ting; Gong, Hong. 柠檬酸钠与草酸铌合成NaNbO3粉体的反应机理 (lit. Study on the synthesis mechanism of NaNbO3 powder from sodium citrate and niobium oxalate). Huaxue Gongchengshi (Chemical Engineer), 2011 (3): 56-58
Rb3[NbO(C2O4)3]·2H2O is a colourless crystal, which includes the [NbO(C2O4)3]3- anion.Šestan, M., Perić, B., Giester, G. et al. Another Structure Type of Oxotris(oxalato)niobate(V): Molecular and Crystal Structure of Rb3[NbO(C2O4)3]⋅2H2O. Struct Chem (2005) 16: 409. doi:10.1007/s11224-005-3111-7 Sr3[NbO(C2O4)3]2·8H2O is a compound containing the same anion, forming the anhydrous at 200°C, starting to decompose at 260°C, and at 875°C it decomposes to SrCO3 and SrNb2O6.Marta, L., Zaharescu, M. & Macarovici, C.G. Thermal and structural investigation of some oxalato-niobium complexes. Journal of Thermal Analysis (1983) 26: 87. doi:10.1007/BF01914092
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