Zirconium halides ZrHal4 (Hal = Cl, Br, I) are volatile and have been used as precursors for CVD of zirconium – containing compounds.
ZrHal4 have been synthesized by following ways:
a). Reduction from oxide in the presence of halogen: ZrO2 + 2 C + 2 Cl2 → ZrCl4 + 2 CO
b). Direct reaction of metallic Zr with halogen: Zr + 2 I2 → ZrI4 (Arkel-de-Boer process)
Properties of zirconium halides:
ZrCl4: colorless solid, mp. 437 °C, bp.331 °C (sublimes), polymeric (below), CN= 6.
ZrBr4: colorless solid, mp. 450 °C, polymeric, coordination No. 6.
ZrI4: yellow solid, mp. 500 °C, polymeric, CN= 6
Thermal decomposition of ZrI4 gives Zr (“hot-wire” CVD process, reverse Arkel-de-Boer!), reaction efficiency of 0.32 at 1152 °C[[i]]: ZrI4 -> Zr + I2
[i] Prof. Dr. Heinrich Lang,, The Chemistry of Metal CVD, International Research Training Group, “Materials and Concepts for Advanced Interconnects”