Four-electron reduction of dioxygen catalysed by dinuclear cobalt complexes bridged by bis(terpyridyl)anthracene.

Dinuclear cobalt-1,10-phenanthroline (1) and 2,2'-bipyridine (2) complexes bridged by 1,8-bis(2,2':6',2''-terpyrid-4'-yl)anthracene (btpyan) were prepared. Both of the complexes selectively catalysed the electrochemical four-electron reduction of dioxygen to H2O without the generation of H2O2 as a two-electron reduction product.

Controlled super-structures of hydrogen bonding Ni(II) complexes organizing one-dimensional double cationic arrays.

Anionic tris-biimidazolato Ni(II) complexes ([Ni(Hbim)3]-), which represent a hydrogen-bonding molecular building blocks, are self-organized to form honeycomb-sheet super-structures connected with complementary intermolecular hydrogen bonds by cations in the crystal. The crystal formed by the stacking of the sheets has nano-channel structures having width of ca. 2 nm-scale width, which confines one-dimensional double columnar arrays of cationic molecules. Thus, relative large cations such as potassium crown-ether complexes and PPh4+ can generally cause [Ni(Hbim)3]- to assemble to a honeycomb-sheet formation forming these channel structures. However, smaller cations such as 4-phenylethyl pyridinuim and trimethyl ethynyl ammonium also lead to the same honeycomb-sheet network by forming the cationic ion-pairs containing an anion in the channels; this is a new finding that we present in this paper.

Electric double-layer capacitance of carbon nanocages.

We have carried out capacitive experiments on carbon nanocage (CNC) materials, which have highly ordered and uniform pores. The sizes of the opening pores in CNCs are approximately 5.6 nm, as measured from TEM images. CNC materials exhibit type IV nitrogen adsorption isotherms according to the IUPAC classification scheme along with hysteresis and BJH desorption pore size distributions of about 5.2 nm, with high BET surface areas of 1515 m2 x g(-1) and large pore volumes of 2.0 cm3 x g(-1). The density and specific surface area of the CNC thin film were 0.289 g x cm(-3) and 366 m2 x cm(-3), and those of the AC-A film, compared with that of the most popularly employed activated carbon, were 0.608 g x cm(-3) and 671 m2 cm(-3) by the CV measurement, respectively. The gravimetric capacitance (ca. 200 F x g(-1)) for the CNC modified electrode is almost equal to that of the AC-A electrode; however, the volumetric capacitance of the CNC electrode (ca. 50 F x cm(-3)) is only half that of the AC-A electrode, suggesting that the pore spaces in the CNC material are much larger than those in AC-A, and large interfaces in these spaces are not favorable for EDLCs.

Experimental and theoretical evaluation of the charge distribution over the ruthenium and dioxolene framework of [Ru(OAc)(dioxolene)(terpy)] (terpy = 2,2':6',2' '-terpyridine) depending on the substituents.

A series of ruthenium complexes [Ru(OAc)(dioxolene)(terpy)] having various substituents on the dioxolene ligand (dioxolene = 3,5-t-Bu2C6H2O2 (1), 4-t-BuC6H3O2 (2), 4-ClC6H3O2 (3), 3,5-Cl2C6H2O2 (4), Cl4C6O2 (5); terpy = 2,2':6'2' '-terpyridine) were prepared. EPR spectra of these complexes in glassy frozen solutions (CH2Cl2:MeOH = 95:5, v/v) at 20 K showed anisotropic signals with g tensor components 2.242 > g1 > 2.104, 2.097 > g2 > 2.042, and 1.951 > g3 > 1.846. An anisotropic value, Deltag = g1 - g3, and an isotropic g value, g = [(g1(2) + g2(2) + g3(2))/3]1/2, increase in the order 1 < 2 < 3 < 4 < 5. The resonance between the Ru(II)(sq) (sq = semiquinone) and Ru(III)(cat) (cat = catecholato) frameworks shifts to the latter with an increase of the number of electron-withdrawing substituents on the dioxolene ligand. DFT calculations of 1, 2, 3, and 5 also support the increase of the Ru spin density (Ru(III) character) with an increase of the number of Cl atoms on the dioxolene ligand. The singly occupied molecular orbitals (SOMOs) of 1 and 5 are very similar to each other and stretch out the Ru-dioxolene frameworks, whereas the lowest unoccupied molecular orbital (LUMO) of 5 is localized on Ru and two oxygen atoms of dioxolene in comparison with that of 1. Electron-withdrawing groups decrease the energy levels of both the SOMO and LUMO. In other words, an increase in the number of Cl atoms in the dioxolene ligand results in an increase of the positive charge on Ru. Successive shifts in the electronic structure between the Ru(II)(sq) and Ru(III)(cat) frameworks caused by the variation of the substituents are compatible with the experimental data.