Olive-green cobalt(III) complexes having the general formula Co4O4(O2CMe)4L4 (1) where L = py (1a), 4-Mepy (1b), 4-Etpy (1c), and 4-CNpy (1d) have been prepared by the H2O2 oxidation of a mixture of Co2+, MeCO2-, and pyridine or 4-substituted pyridines in a 1:2:1 molar ratio in methanol. Spectroscopic and X-ray crystallographic studies show that these complexes contain a tetrameric cubane-like core [Co4(mu3-O)4]4+ where the four cobalt atoms form an approximate tetrahedron with edge lengths of approximately 2.75 A. Each cobalt in the crystallographically determined structure of Co4(mu3-O)4(mu-O2CMe)4L4 in 1a.NaClO4.3.5H2O and 1b.3H2O is hexacoordinate. Infrared spectra of the complexes show characteristic bands near 700, 635, and 580 cm-1 due to the central cubane-like core. 1H NMR spectra of the complexes show that the dissolved species are essentially diamagnetic and also that the complexes maintain their integrity in solution. UV-vis spectra of the green solutions have been interpreted in terms of ligand-field and charge-transfer bands. The electrochemical behavior of the complexes studied by cyclic and differential pulse voltammetric techniques indicates that the [(CoIII)4(mu3-O)4]4+ core present in the complexes undergoes a reversible one-electron oxidation to the [(CoIII)3CoIV(mu3-O)4]5+ core with an E1/2 value below 1 V. This suggests that these complexes of cobalt may be suitable as catalysts for the oxidation of organic compounds. Preliminary investigations indicate that 1a has a role to play in the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene.

Molecules in metal isonicotinate tetrahydrates, M(NC 5 H 4-p-CO 2) 2 .4H 2 O with M = Mn, Fe, Co, Ni, Cu, Zn, consisting of the hexacoordinate complexes trans-[M(NC 5 H 4-p-CO 2) 2 (OH 2) 4 ], participate in exhaustive hydrogen-bond formation among themselves to lead to a robust 3D supramolecular network in the solid state. Solid-state diffuse reflectance UV-Vis-NIR spectra of the complexes have been assigned to ligand field and charge transfer transitions. Sharp weight loss due to dehydration, as shown by TGA of Cu(NC 5 H 4-p-CO 2) 2 .4H 2 O, suggests the suitability of this complex for the gravimetric estimation of copper.

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Two efficient catalysts based on trinuclear Mn(ii)/Zn(ii) clusters were synthesized and used for ipso-hydroxylation of phenylboronic acids into the corresponding phenols with excellent yields.