3 сентября, 2015 
Pokraskin Metal-complex dyes are coordination compounds in which a metal ion is linked to one or more ligands containing one or more electron-pair donors. Ligands with one and more donor groups are called mono-, di-, trifunctional ligands, etc. Coordination of two or more of the donor groups of such ligands to the same metal atom leads to di-, tri-, or tetradentate chelation, etc.; other names for these ligands are thus chelating agents or chelators. The metal complexes of these ligands are called chelates. The metals in metal-complex dyes are predominantly chromium and copper, and to a lesser extent cobalt, iron, and nickel.
The first use of metal-complex dyes was the process of mordant dyeing, a method that can be traced to the Middle Ages. Here the textile fabrics to be dyed were impregnated with a solution of salts of a metal such as aluminum, iron, chromium, or tin and then treated with a naturally occurring colorant containing a chelating system to achieve metallization within the fiber. The mordant dyeing leads to a bathochromic shift in color, albeit with duller hue, and to improved resistance to light and washing.
In the 1940s the so-called afterchrome method was developed and gained commercial importance, particularly in the dyeing of wool in dark shades with high fastness. In this process a chromium complex was formed on the fiber by first dyeing with a metallizable dye followed by aftertreating the dyed fabris with sodium or potassium dichromate (M2Cr2O7*2H2O) or chromate (M2CrO4). Two other chrome methods, namely, the mordant chrome and the metachrome techniques, were employed. The former is a variant of the above-mentioned mordant dyeing process. It involves treating wool with sodium dichomate and an agent such oxalic acid to reduce chromium in the trivalent state and then dyeing with a chelating azo dye. In the metachrome method the dyeing and chroming are performed in a single bath containing the dye, sodium dichromate, and ammonium sulfate. This process has attained only limited application, since it requires dyes which are not oxidized by chromate in the dyebath.
Besides the afterchrome dyes premetallized dyes became commercially important and remained so until to the present day.
The milestones of the metal-complex dyes can be summarized as follows
[1,2]:
1887 Synthesis of the first metallizable azo dye, Alizarin Yellow (R. Nietzky)
1891 Formulation of the theory of coordination (A. Werner)
1893 Synthesis of the first metallizable 2,2′-dihydroxyazo dye (E. Bergmann and O.
Borgmann)
1908 Elucidation of stereochemistry of metal complexes (A. Werner) 1912 Synthesis of the first premetallized 1:1 chromium complex (R. Bohn, BASF)
1920 Marketing of 1:1-chromium complex dyes as Palatin Fast serie (BASF) and Neo — lan serie (Ciba)
1927 First synthesis of copper phthalocyanine (H. de Diesbach and E. von der Weid)
1949 First water-soluble 1:2 chromium complexes lacking sulfo groups (G. Schetty,
Geigy).
1962 Unsymmetrical 1:2 complex dyes containing only one sulfo group 1970 1:2 chromium complexes with two sulfo groups
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