Azo/Azomethine Complex Dyes

From the viewpoint of stereochemistry the most interesting metal complexes are the octahedrally coordinated 1 2 chromium and cobalt complex dyes, which are medially metallized azo and azomethine compounds with functional groups in the o- and o -positions. Three types of isomerism can be discriminated geometrical, N-a, 3, and that arising from azo-hydrazone tautomerism. 

By far the most important and widely used metal-complex dyes are derived from azo compounds. Although they deliver a multitude of shades, only a few basic components are necessary to produce metal-complex azo dyes. The most useful starting materials are the amines 1-4, which serve as diazo components for reaction with suitable coupling components to give tridentate azo ligands. In addition, the amines 1 and 2 can be condensed with salicylaldehyde or arylazo-substituted salicylaldehydes to give tridentate azomethine ligands. 

This chapter is concerned with dyes and pigments which are complexes of azo, formazan, azomethine, nitroso, anthraquinone and phthalocyanine ligands. Many of these compounds find important applications in other fields, particularly colour photography and reprography, analysis, catalysis, biology, and some modem high technology industries such as electronics. These applications are described in other chapters of this volume. 

Copper Complexes. The preparation of copper and nickel complexes of tridentate metallizable azo and azomethine dyes is easily carried out in aqueous media with copper and nickel salts at pH 4-7 in the presence of buffering agents such as sodium acetate or amines. Sparingly water soluble precursors can be metallized in alkaline medium at up to pH 10 by using an alkali-soluble copper tetram(m)ine solution as coppering reagent, which is available by treating copper sulfate or chloride with an excess of ammonia or alkanolamines [3],... 

Unsymmetrical 1 2 chromium complexes based on an azo and an azomethine dye ligand can be prepared directly from a mixture of a 1 1 chromium complex and equimolar quantities of an 2-aminophenol, an anthranilic acid, or an aliphatic amino acid, and of salicylicaldehyde or a substituted salicylaldehyde [22],... 

Metal complexes of azo and azomethine dyes are an important class of industrially relevant pigments. Such pigments possess more advantageous properties compared to their parent chromophore including bathochromic shift of absorption, better weather- and lightfastness and enhanced solvent resistance [90]. 

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