Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 4. UV-Visible Spectral and Electrochemical Evidence of the Remarkable Electron-Deficient Properties of the New Tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazinatometal Octacations, [(2-Mepy) 8 TPyzPzM] 8+ (M ) Mg II (H 2 O), Co II , Cu II , Zn II ) Costanza Bergami, § Maria Pia Donzello, § Fabrizio Monacelli, § Claudio Ercolani,* ,§ and Karl M. Kadish* ,# Dipartimento di Chimica, UniVersita ` degli Studi di Roma “La Sapienza”, p.le A. Moro 5, I-00185 Roma, Italy, and Department of Chemistry, UniVersity of Houston, Houston, Texas 77204-5003 Received June 30, 2005 Metal derivatives of the octacationic tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine macrocycle [(2-Mepy) 8 TPyzPzH 2 ] 8+ (2-Mepy ) 2-(N-methyl)pyridiniumyl ring) isolated as water-soluble hydrated iodide salts of the general formula [(2-Mepy) 8 TPyzPzM](I 8 )‚xH 2 O, (M ) Mg II (H 2 O), Co II , Cu II , Zn II ; x ) 2-5) were prepared from the corresponding neutral complexes [Py 8 TPyzPzM]‚xH 2 O previously reported. Reaction of these complexes with CH 3 I in N,N-dimethylformamide under mild conditions led to full quaternization of all eight pyridine N atoms and formation of the octacations [(2-Mepy) 8 TPyzPzM] 8+ . Clathrated water molecules could be eliminated from the species [(2-Mepy) 8 TPyzPzM](I 8 )‚xH 2 O by mild heating (e100 °C) under vacuum, but the unsolvated species which were formed tended to rehydrate when exposed to air. Magnetic susceptibility measurements and EPR spectra prove that the Cu II and Co II complexes in the solid state are both paramagnetic with one unpaired electron, thus giving a low-spin state Co II for the latter compound. Studies of the charged species [(2-Mepy) 8 TPyzPzM] 8+ in aqueous media at ca. 10 -5 M concentration provide evidence for the occurrence of molecular aggregation, similar to what is seen for the related free-base species [(2-Mepy) 8 TPyzPzH 2 ] 8+ (see part 3 of this series, preceding paper in this issue), but the formation of monomeric species is generally favored upon dilution of the solutions. The same octacations are essentially monomeric in solutions of pyridine or dimethyl sulfoxide (DMSO), but traces of aggregation, if occasionally present, vanish with the time. Changes in the UV-visible spectra are observed in the Q- and B-band regions as a result of the quaternization at the pyridine N atoms. Cyclic voltammetry and thin-layer spectroelectrochemical data in DMSO show well-resolved reversible multistep one-electron reductions for both the unmethylated and methylated complexes, all of which appear to be ligand-centered, the only exception being reduction of the Co II complex. For this species, the first one-electron reduction is a metal-centered Co II f Co I process, but the site of electron transfer is reversed and the final product upon a further one-electron reduction is formulated as a Co II dianion as opposed to a Co I π-anion radical. This sequence is similar to what was earlier reported for reduction of the same compound in pyridine. Reversible one-electron oxidations are also observed for the unmethylated species [Py 8 TPyzPzM]‚xH 2 O where M ) Co II and Mn II in DMSO. Remarkably, the octacationic macrocycles [(2-Mepy) 8 TPyzPzM](I 8 )‚xH 2 O, (M ) Mg II (H 2 O), Co II , Cu II , and Zn II ; x ) 2-5) are more easily reduced at any step of the reduction than the corresponding unquaternized species with the same metal ion. This indicates a higher tendency to stepwise electron uptake after the quaternization process, which enhances the charge redistribution capability within the species formed by the electroreduction. Introduction In recent years the synthesis and characterization of new porphyrazine macrocycles carrying strongly electron with- drawing heterocyclic rings annulated at the peripheral sites of the central porphyrazine core has attracted our interest (see ref 5 in the previous companion paper to this work 1 ). A * To whom correspondence should be addressed. E-mail: claudio.ercolani@uniroma1.it (C.E.), kkadish@uh.edu (K.M.K.). § Universita ` degli Studi di Roma “La Sapienza”. # University of Houston. Inorg. Chem. 2005, 44, 9862-9873 9862 Inorganic Chemistry, Vol. 44, No. 26, 2005 10.1021/ic051085d CCC: $30.25 © 2005 American Chemical Society Published on Web 11/19/2005