Phthalocyanine polymorphic forms

However, there are metal complex pigments. Without doubt the most important metal complex pigment is copper phthalocyanine (4). The phthalocyanines were discovered by accident in 19286 and now represent the second most important class of colorants after the azo colorants. Copper phthalocyanine itself exists in several polymorphic forms and gives beautiful blue and cyan colors with outstanding fastness properties.5-7 Halogenated copper phthalocyanines provide green pigments (see Section 9.12.4.3). 

The synthesis of linear turns-quinacridone (2.38) was reported in 1935 by Liebermann [26] and was cursorily looked at as a red vat colorant but not developed commercially. It was more than twenty years later that the DuPont company introduced these compounds as pigments under the trade name of Cinquasia. Their chemical structures are based on Cl Pigment Violet 19 (2.38). As with the phthalocyanines, this compound can exist in several polymorphic forms in this case there are three, termed a-, p- and y- forms only the last two being useful as pigments. The first three pigments were called Cinquasia Red B (y-form, size above 1000 nm), Cinquasia Red Y (y-form, size below 1000 nm) and Cinquasia Violet R (P-form). 

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. 

Metal-free phthalocyanine (H2PC) exists in the a, P, r, and X polymorphic forms. The a,P, and X forms have been characterized by electrochemistry [36a], fluorescence spectroscopy [36b], and optical absorption [36c] and a,p, and t forms by C-NMR spectroscopy [36d], optical absorption, and X-ray powder diffraction [36e]. Figure 19 shows the optical absorption spectra of the four forms. The t form has been further characterized as to particle shape (Types I and II) [36f]. The as-synthesized y9-H2Pc is converted to a-H2Pc by acid pasting and this can be converted to the X or T forms with mechanical milling under specific conditions. The X and r forms convert to the P with thermal, solvent, or extended mechanical treatment. 

Dichlorostannic phthalocyanine undergoes a very interesting reaction with disodium phthalocyanine to form the unique bis(phthalocyanine)-tin(IV) (XLVI) (10), which is a distinct homogeneous phase (374), and which has been shown to contain quadrivalent tin by quantitative oxidation (89). Two polymorphs of (XLVI) are known, a and /J. The form purified by vacuum sublimation is converted to the a form when crystallized from naphthalene or 1,2,4-trimethylbenzene. Their infrared spectra are very similar, but they differ in their X-ray powder photographs. The d spacings (A) of the three strongest lines (visually estimated intensities in parentheses) are (195) ... 

In crystals of the copper phthalocyanine fairly rigid molecules can be packed in different arrangements giving rise to different polymorphs. In literature ten different polymorphic forms of copper phthalocyanine are described (Erk Hengelsberg, 2003). From all polymorphic forms commercial interest exhibits the first recognized a form and the most thermodynamically stable p form. 

Each polymorphic form of phthalocyanine is built from molecules arranged in uniform stacks with rings tilted with respect to the stacking direction. For the a and P forms the molecules are tilted in stacks with respect to the stacking direction by 25 and 46 respectively. 

In the case of PcCu and PcH2, the most stable modification, which is formed during synthesis, is the -modification. For a more detailed discussion on the polymorphism in phthalocyanines, see refs 36 and 76. 

Quinacridone is the trivial name given to the five-ring heterocyclic system exemplified by the linear irani-quinacridone (2.69). The yellow-red to reddish-violet shade pigments based on this ring system show outstanding durability and are used in plastics, in industrial and automotive finishes and in exterior finishes. Like copper phthalocyanines the unsubstituted linear quinacridone exhibits polymorphism and two crystal forms, the reddish violet P-form and the red y-form, are commercially... 

As already stated most phthalocyanines exhibit polymorphism, and many of these morphological forms absorb in the near-IR, especially in the solid state. For instance, in the case of the metal-free, unsubstituted parent phthalocyanine, usually designated... 

Most phthalocyanines show inferior dark decay to azo pigments, an exception being the titanyl phthalocyanines, where in the best cases, e.g. the a- and Y- forms, they show comparable dark decay coupled with superior photosensitivity. A comparison of the sensitivity of azo pigments and selected polymorphs of phthalocyanines is shown graphically in Figure 4.12. 

Solid /8-CrPc reacts reversibly with gaseous NO at ambient temperature to give a 1 1 adduct, which reacts with both py and 02 (Scheme 117).596 No structural information is available on the oxidation product of the nitrosyl complex. In contrast to the /3 form, solid ar-CrPc is unreactive towards either 02 or NO, a difference ascribed to the solid-state structures of the two polymorphs.597 Although the distance between the phthalocyanine planes is similar (340 pm), in both cases the metal-metal distance increases from 340 to 480 pm on going from the a to the /3 form. These distances are sufficient to permit access of 02 or NO in the /8 form, while excluding them from the a form. The addition of py to CrPc(NO) causes the NO stretching band in the IR spectrum to intensify and to sharpen considerably. The diffuse nature of this band in CrPc(NO) indicates the presence of a perturbed NO ligand but the introduction of py causes lattice expansion and eliminates the perturbation. 

The macrocyclic phthalocyanine ligand will form a complex Pt(phthalocyanine).1106 The crystal structure shows two polymorphs present because of molecular packing.1107 The platinum is in a square planar coordination geometry with a mean Pt—N distance of 1.98 A. The complex can be partially oxidized with iodine to give conducting mixed valence solids.1108 Eighteen fundamental and overtone combination bands are observed in the resonance Raman spectrum of platinum phthalocyanine, and from this data the symmetry of the excited singlets are found to be Dy.. Qlv or D2.1109... 

Copper Phthalocyanine Blue. CPC blue exists in several polymorphic modifications, two of which, the red-shade blue alpha and greenshade blue beta form, are of great commercial significance. Beta is the thermodynamically more stable phase and is the product resulting from manufacture by the two basic processes using either phthalonitrilc or phthalic anhydride as starting materials. The alpha form is usually obtained by conversion from the beta form and has to be stabilized to prevent phase reconversion. 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

Of the metallophthalocyanines that crystallize in forms other than the a-, j3-, and y-polymorphs, the most notable are Pb(pc)2031 and Ga(pc)F1301. The Pb(pc) molecules are stacked metal-over-metal, as shown in Fig. 28, and the Pb-Pb spacing is 3.73 A. The phthalocyanine ring deviates markedly from planarity, although the separate isoindole moieties retain their planarity. In Ga(pc)F the Ga atoms are symmetrically bridged by F, with a Ga-F distance of 3.92 A the pc rings are eclipsed, rather than staggered1301. 

Molecular complexes, such as the complex formed between poly(N-vinylcaibazole) and 2,4,7-trinitro-9-fluorenone, and dye-polymer aggregates were widely used as generation materials in many early applications. Since these materials are not infrared sensitive, there has been increasing emphasis on pigments. The more widely studied are various azo, phthalocyanine, squaraine, and peiylene diimide derivatives. A common feature of all of these materials is that they are polymorphic and exist in many different crystal forms. The properties are thus very sensitive to the conditions used in their preparation. Further, the sensitivity of these materials is strongly field dependent as well as dependent on the transport material. For a review of generation materials, see Law (1993). 

Law (1993) has reviewed the widespread polymorphism in phthalocyanines and its relationship to their photoconductivity and use in xerographic applications. These are best demonstrated by the prototypical copper phthalocyanine CuPc (6-XIX, M = Cu), whose structural chemistry is discussed in detail in Section 8.3.3.1. The polarized absorption spectra of five forms are given in Fig. 6.9. One outstanding feature of these spectra is the rather intense red shifted band at 770 nm in the 5 and modifications compared to the solution absorption at 678nm (Law 1993). This... 

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