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In situ Mossbauer spectra revealed changes in the electronic and structural properties of Fe sites brought about by redox processes attributed formally to Ni sites in a composite iron/nickel hydroxide. Measurements on the oxidized form, polarized in 1 M KOH at 0.5 V vs. Hg/HgO, revealed a singlet with an isomer shift of 0.22 mm/s vs. a-Fe. After reduction and polarization at 0.0 V, a doublet with an isomer shift of 0.32 mm/s and a quadrupole splitting of 0.44 mm/s was observed. The spectral changes, which accompanied the formal oxidation of Ni sites at 0.5

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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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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