Han Purple

Han Purple represents the first synthetic pigment containing a metallic bond. Its natural analog compound has been found in the Wessels mine, Kalahari Manganese Field (South Africa) as the natural mineral colinowensite but also in this case it is unlikely that the mineral was used as pigment since it is quite rare in nature. The interest in this compound is not only related to its artistic use. In fact, the rare arrangement of the Cu ions and being a quasi-2D material displaying anomalous critical properties has attracted the interest of the physics community.
All three pigments’ colors derive from the square-planar ???6−4 chromophore. Moreover, HB and EB share the same structure (tetragonal space group P4/ncc).