Zirconium tetrachloride revisited

Zirconium tetrachloride, ZrCl₄, is a strategic material with wide-ranging applications. Until now, only one crystallographic study on ZrCl₄ has been reported [Krebs (1970). Z. Anorg. Allg. Chem. 378, 263-272] and that was more than 40 years ago. The compound used for the previous determination was prepared from ZrO₂ and Cl₂-CCl₄, and single-crystal X-ray diffraction (SCXRD) studies on ZrCl₄ obtained from Zr metal have not yet been reported. In this context, we prepared ZrCl₄ from the reaction of Zr metal and Cl₂ gas in a sealed tube and investigated its structure at 100, 150, 200, 250, and 300 K. At 300 K, the SCXRD analysis indicates that ZrCl₄ crystallizes in the orthorhombic space group Pca2₁ [a = 6.262 (9), b = 7.402 (11), c = 12.039 (17) Å, and V = 558.0 (14) ų] and consists of infinite zigzag chains of edge-sharing ZrCl₆ octahedra. This chain motif is similar to that observed previously in ZrCl₄, but the structural parameters and space group differ. In the temperature range 100-300 K, no phase transformation was identified, while elongation of intra-chain Zr...Zr [3.950 (1) Å at 100 K and 3.968 (5) Å at 300 K] and inter-chain Cl...Cl [3.630 (3) Å at 100 K and 3.687 (9) Å at 300 K] distances occurred.