Iron oxychloride

Iron oxychloride is the inorganic compound with the formula FeOCl. This purple solid adopts a layered structure, akin to that of cadmium chloride. The material slowly hydrolyses in moist air. The solid intercalates electron donors such as tetrathiafulvalene and even pyridine to give mixed valence charge-transfer salts. Intercalation is accompanied by a marked increase in electrical conductivity and a color change to black.

Production
FeOCl is prepared by heating iron(III) oxide with ferric chloride at 370 °C over the course of several days:
 * Fe2O3 +  FeCl3   →   3 FeOCl

Alternatively, FeOCl may be prepared by the thermal decomposition of FeCl3⋅6H2O at 220 °C over the course of one hour:
 * FeCl3 ⋅ 6H2O →    FeOCl  +  5 H2O + 2 HCl