NIOBIUMCHLORIDE

Brown-black crystal needles; pure brown in transmitted light.
Decomposes on exposure to air and moisture (color change first to black, then to white). Dissolves in a small amount of H2O and in dilute hydrochloric acid, giving a dark-blue solution.

Reduction of NbCl5 with H2 at 2 atm. (generated when the tube is filled at STP, sealed and then heated). The reaction does not go to completion and NbCl5 and NbCl4 must be separated by sublimation.