CoCl22H2O

Cobalt(II) chloride dihydrate, commonly referred to as CoCl₂·2H₂O, is a coordination compound composed of cobalt, chlorine, and water. It is a well-known chemical with distinctive properties and applications in various fields.

The compound crystallizes in a pink or red form when anhydrous, but its dihydrate form typically appears as a bright blue or purple crystalline solid. This color change is due to the presence of water molecules coordinated to the cobalt ion, altering its electronic structure and absorption spectrum. Upon heating, CoCl₂·2H₂O loses its water molecules, transitioning to the anhydrous form, which is pink or red. This reversible hydration-dehydration process is often used as a simple qualitative test for water.

CoCl₂·2H₂O is soluble in water and polar solvents but insoluble in nonpolar organic solvents. It exists as an octahedral complex, with cobalt in the +2 oxidation state coordinated to four chloride ions and two water molecules in the solid state. In aqueous solution, the water ligands can be replaced by other ligands, depending on the conditions.

This compound has several practical applications. It is used as a catalyst in organic synthesis, particularly in hydrogenation reactions. In analytical chemistry, it serves as an indicator in moisture detection, changing color when exposed to humidity. Additionally, CoCl₂·2H₂O is employed in the preparation of other cobalt compounds and as a pigment in some dyes and ceramics.

Safety considerations include its potential toxicity, particularly when inhaled or ingested, and its ability to act as an oxidizing agent in certain conditions. Proper handling, including the use of protective equipment, is recommended when working with the compound.