Isomorphism pigments

Isomorphous pigments compounds which, for instance, chemically differ only in a single substituent but whose spatial requirements are similar, are frequently more uniform in their physical and application characteristics than is true for polymorphous pigments. 

Any crystal modification is practically fingerprinted by its X-ray diffraction spectrum. Another factor determined by the same instrumentation is isomorphism in chemically different pigments, which is associated with almost equal diffraction angles and X-ray intensities in both experiments. It is also important to ensure that the intensity of the incident beam is approximately the same for both measurements. 

R = -C4H9) has been reported to crystallize in four polymorphic forms (Brandt et al. 1982). In the copper phthalocyanines Pigment Blue 15, containing no Cl, is isomorphous with Pigment Blue 15 1, which on an average contains 0.5-1.0 atoms of chlorine per molecule (Hao and Iqbal 1997). Recognition of this phenomenon can be useful, for instance, in attempting to work out the crystal structures of unknown polymorphic forms. 

Cerussite (PbCOs) is also naturally abundant and crystallizes in an orthorhombic form isomorphous with strontianite (SrCOs) and aragonite (CaCOs). PbCOs is often found with galena in ore veins because it forms when carbonate-rich waters interact with PbS in the common lead-zinc-limestone ore association (47). The derivative PbCOs Pb(OH)2, known as cemse or white lead , was the most important artificial white pigment in antiquity (3). Ceruse is made by treating naturally occurring lead compounds [mixtures of PbCOs, PbO, and... 

The salts FeH2P30io and CrH2P30io are formed in similar dehydration sequences, and the acid salts of all three metals exist in various isomorphous and polymorphic forms. Both CrH2P30io 2H2O and AIH2P3O10 2H2O find use in anti-corrosive pigment formulations. Both salts can form intercalation compounds (Chapter 12). 

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