Formazan tridentate ligand

As far as dyes are concerned, chelates of type Cb are termed 1 2 or symmetrical 1 2 metal complexes if the two tridentate ligands are equal, and mixed or unsymmetrical 1 2 metal complexes in the other case. Chelates of type Bb represent 1 1 metal complexes. The types Cb and Bb include, in general, azo and azo-methine metal complex dyes, whereas chelates of the quadridentate types Ac and Be are derived predominantly from formazan and phthalocyanine chromophores. 

Metal-Containing Tridentate Formazans. Formazans substituted with OH or COOH in the 2-position of the N1- or Ns-aryl group have the same complexing properties as 2-hydroxy- (or carboxy)-2-aminodiarylazo dyes. Similarly, they also form 1 1 complexes with four-coordinate metals, and 1 2 complexes with six-coordinate metals. Being N ligands formazans react more readily with cobalt salts than with chromium salts. The mostly blue 1 2 cobalt(m) complexes of type 34 [72] and the mostly gray-blue complexes of type 35 [73] are known. 

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