Tetrachlorides

Tetrachlorides are chemical compounds that contain four chlorine atoms bonded to a central atom, giving the general formula MX4. They encompass a range of main-group and transition-metal chlorides and are typically covalent and often highly reactive with water.

Common examples include silicon tetrachloride (SiCl4), titanium tetrachloride (TiCl4), germanium tetrachloride (GeCl4), tin tetrachloride (SnCl4), zirconium tetrachloride (ZrCl4), and hafnium tetrachloride (HfCl4). Some, such as SiCl4 and TiCl4, are volatile liquids at room temperature, while others are crystalline solids. The bonding in many MX4 tetrachlorides is covalent, and several act as Lewis acids, engaging with Lewis bases in catalysis or complex formation.

Reactivity is dominated by hydrolysis: exposure to moisture typically yields metal oxychlorides or oxides and hydrogen chloride. For example, TiCl4 hydrolyzes to form TiO2-based species and HCl; SiCl4 hydrolyzes to silica and HCl. Because of their moisture sensitivity, these compounds are usually handled under strictly controlled, dry conditions.

Preparation methods vary by element. SiCl4 is commonly prepared by chlorinating silicon. TiCl4 can be produced by chlorinating titanium oxides or metals under appropriate conditions. Other MX4 compounds are prepared by chlorinating the respective metal or oxide precursors in a suitable reactor setup.

Applications include use as Lewis acid catalysts in organic synthesis, precursors to metal oxides and mixed oxides, and sources of metal chlorides for various industrial processes. They also serve as volatile starting materials for chemical vapor deposition and materials synthesis. Safety considerations center on their corrosivity, moisture sensitivity, and the corrosive HCl released upon hydrolysis, requiring careful handling and storage.