Cobalt(II) perchlorate

Cobalt(II) perchlorate is an inorganic chemical compound with the formula Co(ClO4)2·nH2O (n = 0,6). The pink anhydrous and red hexahydrate forms are both hygroscopic solids.

Preparation and reactions
Cobalt(II) perchlorate hexahydrate is produced by reacting cobalt metal or cobalt(II) carbonate with perchloric acid, followed by the evaporation of the solution:
 * CoCO3 + 2 HClO4 → Co(ClO4)2 + H2O + CO2

The anhydrous form cannot be produced from the hexahydrate by heating, as it instead decomposes to cobalt(II,III) oxide at 170 °C. Instead, anhydrous cobalt(II) perchlorate is produced from the reaction of dichlorine hexoxide and cobalt(II) chloride, followed by heating in a vacuum at 75 °C.

Structure
The anhydrous form consists of octahedral Co(ClO4)6 centers, with tridentate perchlorate ligands. On the other hand, the orthorhombic hexahydrate consists of isolated [Co(H2O)6]2+ octahedrons and perchlorate anions with lattice constants a = 7.76 Å, b = 13.44 Å and c = 5.20 Å. The hexahydrate undergoes phase transitions at low temperatures.