Metal-complex dyes

Metal-complex dyes are a family of dyes that contain metals coordinated to the organic portion. Many azo dyes, especially those derived form naphthols, form metal complexes by complexation of one of the azo nitrogen centers. The insertion of the metal into the organic ligand often involves redox reactions, e.g. pre-reaction of sodium dichromate with glucose. Phthalocyanine (Pc) complexes, such as CuPc, are another important family of metal complex dyes.[1]

Chemical structure proposed for carmine. Also called cochineal, carmine is a pigment derived from a bright-red dye produced by insect.
Illustrative chromium dye derived from azo coupling to an azo-ligand. Two such ligands are attached to the Cr(III) center, giving an overall anion.

References
  1. Klaus Grychtol, Winfried Mennicke (2005). "Metal-Complex Dyes". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_299.
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