Konstitution und Farbe von Alizarin‐ und Purpurin‐Farblacken

Abstract

Constitution and Colour of Alizarin and Purpurin Dyes The colour of madder dyes used as pigment in antiquity and in the last centuries is produced mainly by metal complexes of alizarin ( 1 ) and purpurin ( 2 ). Single crystals of aluminium calcium alizarinate and purpurinate are obtained by two‐phase crystallization. X‐ray structure determinations show tetranuclear complex molecules with four alizarins which are different from formerly proposed structures. Solutions of 17 metal complexes of alizarin in DMF/Water exhibit UV‐Vis spectra the maxima of absorption of which strongly depend on the electronegativity of the metals. A classical explanation for this is given.