Two new series of porphyrazines with exocyclic pended 2-pyridyl and 2-N-methylpyridyl rings were investigated as to their electrochemical properties. The structures of the investigated compounds are shown in Chart 1a and represented in one case as [Py₈PzM], where M = 2H, Mg^II(H₂O), Co^II, Cu^II or Zn^II and in the other as [(2-Mepy)₈PzM]⁸⁺, where M = Mg^II(H₂O) or Zn^II. The redox behavior of these new compounds is then compared to that of earlier synthesized porphyrazines with p-extended systems which are represented as [Py₈PyzPzM] (Chart 1b), and [Py₈QxPzM] where Qx = quinoxaline. Each porphyrazine undergoes multiple one-electron reductions in DMSO, benzonitrile, pyridine or CH₂Cl₂ while the two octacationic porphyrazines, [(2-Mepy)₈PzM]⁸⁺, also exhibit 2 or 3 one electron reductions in water containing 0.1 M NaOAc or 0.1 M KCl as supporting electrolyte. The potentials for each redox reaction were measured by cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry was used to characterize some of the redox reactions. Special emphasis was placed on the cobalt(II) derivative [Py₈PzCo^II]⁺, which is oxdized in a single step to give [Py₈PzCo^III] or reduced in up to five one-electron transfer steps, with the exact potentials and site of electron transfer depending upon the solvent. Pyridine was shown to strongly coordinate to the metal center of [Py₈PzCo^II] and [Py₈PzCo^III] and binding constants were calculated using standard equations. Finally, comparisons are made between redox behavior of the three types of compounds in Chart 1, [Py₈QxPzM] and the well-characterized phthalocyanines, [PcM], having the same central metal ions.

Chart 1. Structures for (a) newly investigated porphyrazines and (b) related porphyrazines with p-extended structures.(In the figure : 1) change formula: [(2-Mepy)₈PzM]⁸⁺ instead of [(CH₃-Py)₈PzM] ; 2) change the order of metal centers and put the oxidation state: M = 2H, Mg^II(H₂O), Co^II, Cu^II, Zn^II instead of M = Mg(H₂O), Cu, Zn^, 2H, Co ; 3) put M = Mg^II(H₂O), Zn^II instead of M = Mg(H₂O), Zn⁾