Oxidation state (IV) for Niobium

Niobium(IV) halides

Niobium(IV) chloride or niobium tetrachloride NbCl4 exists as dark violet crystals, it is highly sensitive to air and moisture, and disproportionates into niobium(III) chloride and niobium(V) chloride when heated.

In the solid state, NbCl4 exists as chains of edge-sharing octahedral with alternating Nb-Nb forming a polymer resulting in the compound’s diamagnetism.

The tetrahalides (NbX4) are dark-coloured polymers with Nb-Nb bonds.

.