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Octaethylporphyrinato-cobalt(II), Co(II)OEP, was studied by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) in frozen solutions of methanol, tetrahydrofuran and pyridine diluted into chloroform. Oxygenation led to the respective paramagnetic superoxo complexes Co(III)OEP • py • O. The EPR spectra demonstrate strong differences in the axial ligation states ((base-on)/(base-off)) and ease of the oxygenation process. Additional ENDOR studies with partial orientation selection along the principal g tensor axes are performed for resolution of the 'H, 4115N and 59 Co hyperfine coupling constants. This allows a comparison of the electron spin density distribution of the superoxo complex and its precursor. The data are interpreted in the framework of a more rigorous and detailed theoretical configuration interaction model than previously presented in the literature. The theoretical treatment shows that the structure of the superoxo complex is best described in a three-orbital model with contributions from the cobalt 3d, 4s, and oxygen it orbitals. The analysis reproduces the experimental g and Co hyperfine data yielding the relative energies of the MO's and the MO coefficients for the description of the spin density distribution in the Co(II) complex and its superoxo complex. To demonstrate the generality of the approach and possible applications, a comparison is made with the vitamin B, 2 , system. Furthermore, it provides detailed insight into the electronic and geometric changes resulting from axial ligation and oxygenation of the Co(II)OEP complex; this information can be used for predictions of the catalytic activity.

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The synthesis o f bis(dim ethylglyoxim ato)-cobalt(II) (C oH(dm gH )2) in the a-cages o f a cobalt-exchang ed sodium X-zeolite is described. A sim ple hydration/oxygenation sequence culm inating in a superoxo com plex, C oni(dm gH )2-H 20 -0^ has been studied using X-band EPR spectroscopy. The identification o f the precursor species: square-planar C on (dm gH )2, distorted C o H(dm gH )2 and C o M (dm gH)2-2 H20 was aided by com parison o f their g-and 59C o hyperfine tensor principal values with those o f model com plexes. On the basis o f this identification the reaction sequence is discussed.

The photophysics and cyclic voltammetry of two novel phosphorescent thiones, 2,2-dimethyl-indan-1-one-3-thione (DMIKT) and 2,2-dimethyl-indan-1,3-dithione (DMIDT), and three known phosphorescent thiones, 4H-pyran-4-thione (PT), 4H-1-benzopyran-4-thione (BPT) and 2,2-dimethylindan-1-thione (DMIT), have been characterised and compared. The phosphorescence emission of DMIT, DMIKT and DMIDT extends from the red into the near-IR spectral region. The additional carbonyl or thione group of DMIKT and DMIDT causes a significant shift in the emission maxima to 680 nm compared to that of DMIT, at 637 nm, in perfluorinated hydrocarbons. In acetonitrile the emission maxima of DMIKT and DMIDT are at 696 and 706 nm, respectively, and the spectra show vibronic bands which extend out beyond 850 nm. There is a significant reduction in triplet lifetime along this series (from 44 (+/-2) micros (DMIT) to 10 ((+/-0.8) micros (DMIKT) in perfluorinated solvents, and 8.6 (+/-0.5) (DMIT), 1.3 (+/-0.5) (DMIKT) and 0.35 (+/-0.07) micros (DMIDT) in acetonitrile), as well as a reduction in the rate constant for ground-state quenching of the triplet, (from 9.8 ((+/-0.9) to 3.5 ((+/-0.6) and 1.3 ((+/-0.2)x10(9) mol(-1) dm3 s(-1) for the same compounds). The addition of the C=O or C=S groups also causes a decrease in phosphorescence quantum yield with the highest emission quantum yield obtained for DMIT (PhiP=0.149 (+/-0.015)). Electrochemical studies show that while PT and BPT exhibit irreversible redox behaviour, DMIT, DMIKT and DMIDT all show at least one reversible reduction wave attributed to a one-electron process centred on the C=S moiety. The suitability of these lumophores for use in OLEDs is discussed.

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