Metal complexes pigments from

Kondo, T., Oyama, K., and Yoshida, K., Chiral molecular recognition on formation of a metalloanthocyanins a supramolecular metal complex pigment from blue flowers of Salvia patens, Angew. Chem. Int. Ed. Engl, 40, 894, 2001. 

In general, metal complexes formed from bidentate azo chromogens are little used as dyes but do find important applications as pigments (section 2.3.2). Rare exceptions exist, however, such as the nickel(II) complex of p-nitroaniline— BON acid (5.11). This has been used for bordeaux prints of high light fastness on cotton fabrics. Two possible modes of bidentate attachment to the nickel atom can be envisaged (Scheme 5.2). 

Apart from alizarin lake , which is now being formulated as an aluminum/cal-cium complex [3] (Sec. 3.6.2), the oldest known metal complex pigment is an iron complex. In 1885,0. Hoffmann reported on the iron complex of l-nitroso-2-naph-thol, which under the name of Pigmentgriin B (Pigment Green 8,10006) was first industrially exploited in 1921 by BASF. 

The commercially most interesting metal complex pigments within the azo series are those obtained from aromatic o,o -dihydroxyazo compounds, while important products within the azomethine series are nickel or copper complexes of aromatic o,o -dihydroxyazomethine compounds. 

Commercially available azo and azomethine metal complex pigments cover the spectral range from considerably greenish to reddish yellow and yellowish orange. Compared to their parent structures (the corresponding azo and azomethine compounds), azomethine metal complexes frequently exhibit a distinctly duller shade. Formation of the metal complex often shifts the color of an originally yellow material in the greenish yellow direction. 

Further, stable 2 1 transition metal complex pigments 27 (C.I. Pigment Yellow 177) and 28 (C.I. Pigment Yellow 179), featuring six-ring chelates, have been prepared from methine and azomethine type isoindolinones l... 

The l-phenylazo-2-naphthol (7) and particularly the 2-phenylazo-l-naphthol (8) systems are used extensively, providing many of the commercial metal complex azo colorants. Azo pigments are derived from (7) whilst azo dyes are obtained from (8). Both these types of colorant exist predominantly, if not exclusively, in the hydrazone tautomeric form.8,9... 

It is important for metal complex compounds to be free from solubilizing groups in order to provide the necessary pigment characteristics. 

All polycyclic pigments, with the exception of triphenylmethyl derivatives, comprise anellated aromatic and/or heteroaromatic moieties. In commercial pigments, these may range from systems such as diketopyrrolo-pyrrol derivatives, which feature two five-membered heteroaromatic fused rings (DPP pigments) to such eight-membered ring systems as flavanthrone or pyranthrone. The phthalo-cyanine skeleton with its polycylic metal complex is somewhat unique in this respect. 

At present, synthetic routes to more than 40 metal complexes other than the copper complex are known. Apart from a cobalt phthalocyanine pigment (P.B.75) which was introduced to the market just recently, none of the resulting products, however, has stimulated commercial interest as a pigment. Nickel complexes, however, are found in reactive dyes, while cobalt complexes of this basic structure are employed as developing dyes. 

The preparation of chromium(III) and cobalt(III) complexes of tetradentate formazans in which the coordination sphere of the metal is completed by a variety of neutral ligands has been reported116 and these (185) were claimed to be very stable towards acids. By analogy with copper complexes, however, some doubt must exist regarding the structures assigned to those complexes derived from l,5-bis(2-carboxyphenyl)formazans. Various dyestuff and pigment applications have... 

The problem of the origin of the metal-porphyrins is closely related to that of the origin of petroleum and is oie of the most basic and interesting questions of petroleum geochemistry. The most probable conclusion seems to be that the nickel and vanadium porphyrin complexes are formed by metal exchange reactions from animal and/or plant metabolic pigments such as hemoglobin and chlorophyll. 

---