Metal macrocyclics metallophthalocyanine

Phthalocyanine itself is best prepared3 by self-condensation of phthalimidine, which is available from the reaction of phthalonitrile with ammonia. However, in many cases, direct metalation of the macrocycle cannot be achieved. Instead, metalation by means of dilithium phthalocyanine or a template reaction, whereby the macrocycle is formed around the metal using phthalonitrile (or one of its derivatives), must be employed for the synthesis of metallophthalocyanins. 

Figure 2.3. Structures of different MN4 macrocycles. 1 metallophthalocyanine, 2 metal tetraphenylporphyrin, 3 metal tetraazaanuulene, and 4 metal tetramethoxyphenyl porphyrine.

The reaction between phthalonitrile and metals (finely divided or acid etched) is usually very vigorous at 250-300°C and sufficient heat is generated to maintain the reaction temperature. These compounds are monofianctional with respect to the formation of phthalocyanine rings [42,56-58]. The cyclo-tetramer-ization of four phthalonitrile molecules into a phthalocyanine macrocycle involves a reduction reaction which requires two electrons in addition to the 16 Ti-electrons from the 8 nitrile groups to yield the 18 7r-electron aromatic system. For metallophthalocyanine the two extra electrons are provided by metal or metal salts. The use of reducing coreactants such as 1,2,3,6-tetrahydropyridine or hydroquinone is effective for the conversion of phthalonitrile to phthalocyanine. The reactions are normally carried out under pressure. Bis-... 

Fig. 2 Structures of four typically exploited MN4 macrocycles (1) metallophthalocyanine (2) metal tetraphenylporphyrin (3) metal tetraazaanuulene, and (4) metal tetiamethoxyphenyl porphyrine...

Tetrapyrrolic macrocycles, such as porphyrin, consisted of four pyrrole units bonded by different bridges, for example methene in the case of porphyrins and aza-methene in the case of phthalocyanines [1]. These ligands can complex metal ion transition and the synthesized metallocomplexes are extremely stable [2, 3]. While some metalloporphyrins constitute the redox center of naturally occurring proteins, like heme in hemoglobin, metallophthalocyanines are purely synthetic molecules. The (electro) chemical properties of MN4 complexes have been widely studied and have been particularly used for the catalysis of several electrochemical reactions in homogeneous solutions [4]. It was shown that the electrochemical properties of a... 

Except for the macrocyclic modification of phthalocyaninatolead(II) (8) in its monoclinic arrangement, the stacked arrangement has never been observed. Metallophthalocyanines in general crystallize in the a- or B-modifica-tion which is not favourable for x-orbital overlap and thus for the formation of a conduction band. However, if certain transition metal phthalocyanines, e.g. phthalocyaninatonickel(II) are doped with iodine, stacked structures are obtained which exhibit high conductivities (9). 

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