The neutral salt has not been prepared.

[2] 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).

[3] 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;[4] Heating this complex and sodium citrate at 650°C can form sodium niobate (NaNbO3).

[6] 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.