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The cyclic voltammetry of iron phthalocyanine (FePc) and its two q-oxo derivatives obtained by mixing the materials in dry form with high-area Vulcan XC-72 carbon yielded a common set of voltammetric peaks. This provides evidence for the presence of a single type of surface species for the macrocycle in its various forms. The electrochemical activity of these dispersed specimens for 02 reduction in alkaline media using thin porous coating-rotating disk techniques was found to be essentially the same for both ^-oxo derivatives. Comparable activities were observed in the case of bulk monomeric FePc only after polarizing the electrodes at fairly negative potentials. Some differences in activity were observed, however, for the materials in gas-fed electrodes of the type used in fuel cells in 4 M NaOH at 60 °C. Based on the results obtained in this work and quantum mechanical considerations, it has been concluded that (i) the increase in conductivity induced by the exposure of FePc to dioxygen is most likely due to the formation of q-oxo-type derivatives, and (ii) it is not necessary to invoke a metal spin crossover mechanism as the key factor in explaining the high electrocatalytic activity of FePc for the reduction of 02, as has been proposed earlier in the literature.

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In this work, the thin-film/flooded-agglomerate model of gas diffusion electrodes was used to study the oxygen reduction reaction (ORR) on rotating disk electrodes with thin porous coating in alkaline solutions. Vulcan XC-72 carbon and 10, 20, and 30% w/w Pt/C catalysts were used as electrode materials. Fitting of the theoretical equations to the experimental data was employed to simulate the polarization characteristics of the ORR on the catalysts and to obtain the oxygen concentration profiles along the thickness of the flooded agglomerate as a function of the electrode potential and the structural parameters of the electrodes. The method was found to be a simple and adequate way to evaluate the performance of the supported catalysts. The predicted effect of doubling of the Tafel slope of the ORR due to diffusion of the reactant in the flooded agglomerate was confirmed experimentally. The kinetic parameters obtained for the ORR in alkaline media indicated that, for the lower Pt/C ratios, there is a strong participation of the carbon substrate in the catalysis of the reaction.

Reaction of Ni(COD)2 with TBC in benzene affords a planar nickel(0) complex, Ni(TBC), with the nickel atom coordinated equally by all three alkynes of the TBC ligand. The complex crystallizes in the noncentrosymmetric space group Pna21 with a = 15.518 (3) A, b = 18.761 (4) A, c = 5.375 (1) A, V = 1564.8 (5) A3, and 2 = 4. The nickel-carbon and carbon-carbon (alkyne) bond lengths average 1.958 (5) and 1.240 (10) A, respectively. The molecules are slipped-stacked in an eclipsed conformation with an interplanar spacing of 3.35 (1) A. The reaction chemistry of Ni(TBC) with several small molecules including H20, CDC13, CO, COz, 02, and CH&N has been explored. The rates of reaction with CO and O2 are solventdependent. Electrochemical studies of Ni(TBC) and TBC show two reduction waves which are moderately reversible. ASED-MO calculations on Ni(TBC) indicate the HOMO is primarily metal centered, whereas the LUMO is ligand centered. Ni(TBC) is reduced with lithium, sodium, and potassium in various solvents (THF and DME) in the presence of various chelating agents (TMEDA, 18-crown-6, and cryptand-(2.2.2)) to the monoanion and dianion. The material [K(C222)I2[Ni(TBC)] was combined with Ni(TBC) to yield a conducting material. The maximum conductivity (via two-probe powder compaction) was observed to be 2 X (a cm)-' at 0.5 electron per Ni(TBC) unit. A parallel study on TBC showed a maximum conductivity of 8 (2) X 10" (a cm)-' at 0.6 electron per TBC unit. IntroductionTransition-metal complexes of planar metallomacrocycles, including ligand systems such as the porphyrins' and phthalocyanines,2 have been studied in depth as precursors for one-dimensional conductors. These complexes have several key features in common: the molecules are planar with an extended mystem, the ligand atoms which complex the metal are relatively hard nitrogen donors, the ligand has a formal negative oxidation state, and

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