Either Nbl5 or Nbl4 is heated under a vacuum in a horizontally sealed tube, as described in the preparation of Nbl4. The higher iodide is heated to 425-430°C, and the tube end at which the liberated I2 collects is kept at 40°C. The reaction time is 48 hours. The Nbl3 formed can be resublimed in the tube at 450-500°C (partial decomposition).
