Niobium forms halides in the oxidation states of +5 and +4 as well as diverse substoichiometric compounds.
The pentahalides (NbX
₅) feature octahedral Nb centres.
Niobium pentafluoride (NbF₅) is a white solid with a melting point of 79.0 °C and niobium pentachloride (NbCl₅) is yellow (see image at left) with a melting point of 203.4 °C.
Both are hydrolyzed to give oxides and oxyhalides, such as NbOCl₃. The pentachloride is a versatile reagent used to generate the organometallic compounds, such as niobocene dichloride ((C
₅H
₅)
₂NbCl
₂).
The tetrahalides (NbX
₄) are dark-coloured polymers with Nb-Nb bonds; for example, the black hygroscopic niobium tetrafluoride (NbF₄) and brown niobium tetrachloride (NbCl₄).

Anionic halide compounds of niobium are well known, owing in part to the Lewis acidity of the pentahalides.
The most important is [NbF₇]²⁻, an intermediate in the separation of Nb and Ta from the ores.
This heptafluoride tends to form the oxopentafluoride more readily than does the tantalum compound.
Other halide complexes include octahedral [NbCl₆]⁻:
Nb₂Cl₁₀ + 2 Cl⁻ → 2 [NbCl₆]⁻
As with other metals with low atomic numbers, a variety of reduced halide cluster ions is known, the prime example being [Nb₆Cl₁₈]⁴⁻.
Niobium forms halides in the oxidation states of +5 and +4 as well as diverse substoichiometric compounds. The pentahalides (NbX
₅) feature octahedral Nb centres. Niobium pentafluoride (NbF₅) is a white solid with a melting point of 79.0 °C and niobium pentachloride (NbCl₅) is yellow (see image at left) with a melting point of 203.4 °C. Both are hydrolyzed to give oxides and oxyhalides, such as NbOCl₃. The pentachloride is a versatile reagent used to generate the organometallic compounds, such as niobocene dichloride ((C
₅H
₅)
₂NbCl
₂). The tetrahalides (NbX
₄) are dark-coloured polymers with Nb-Nb bonds; for example, the black hygroscopic niobium tetrafluoride (NbF₄) and brown niobium tetrachloride (NbCl₄).
Anionic halide compounds of niobium are well known, owing in part to the Lewis acidity of the pentahalides. The most important is [NbF₇]²⁻, an intermediate in the separation of Nb and Ta from the ores. This heptafluoride tends to form the oxopentafluoride more readily than does the tantalum compound. Other halide complexes include octahedral [NbCl₆]⁻:
Nb₂Cl₁₀ + 2 Cl⁻ → 2 [NbCl₆]⁻
As with other metals with low atomic numbers, a variety of reduced halide cluster ions is known, the prime example being [Nb₆Cl₁₈]⁴⁻.
Niobium