Zirconium(IV) chloride

Zirconium(IV) chloride, also known as zirconium tetrachloride, is ZrCl4. It is a white high-melting solid that hydrolyzes rapidly in humid air. It is a key reagent in the chemistry of zirconium.

Structure
Unlike TiCl4, ZrCl4 adopts a polymeric structure wherein each Zr is octahedrally coordinated. The striking difference in structures, polymeric vs. molecular, is responsible for the striking difference in their properties - one being distillable, the other being a high melting solid. In the solid state, ZrCl4 adopts a tape-like linear polymeric structure--the same structure adopted by HfCl4. This polymer degrades readily upon treatment with Lewis bases, which cleave the Zr-Cl-Zr linkages.

Kroll process
ZrCl4 is the key intermediate in the conversion of zirconium minerals to metallic zirconium by the Kroll process. In nature, zirconium minerals invaribly exists as oxides (reflected also by the tendency of all zirconium chlorides to hydrolyze). To convert these refractory oxides to a metal, they are first converted to the tetrachloride which can be distilled (at high temperatures). This conversion entails treatment of the oxide with carbon as the oxide "getter" and chlorine.
 * ZrO2 +  2 C  +  2 Cl2  →  ZrCl4  +  2 CO

Chemical reactions of ZrCl4
ZrCl4 is the principal starting compound for the synthesis of many organometallic complexes of zironcium. Because of its polymeric structure, ZrCl4 it is usually converted to a molecular complex before use. It forms a 1:2 complex with tetrahydrofuran: CAS [21959-01-3], mp 175-177 °C. NaC5H5 reacts with ZrCl4(THF)2 to give zirconocene dichloride, ZrCl2(C5H5)2, a very versatile organozirconium complex. One of the most curious properties of ZrCl4 is its high solubility in the presence of methylated benzenes, such as durene. This solubilization arises through the formation of π-complexes.

Uses

 * In organic synthesis zirconium tetrachloride is used as a weak Lewis acid for the Friedel-Crafts reaction, the Diels-Alder reaction and intramolecular cyclisation reactions.
 * Used to make pure zirconium and for water-repellent textiles.