Water oxidation by a mononuclear ruthenium catalyst: characterization of the intermediates

A detailed characterization of intermediates in water oxidation catalyzed by a mononuclear Ru polypyridyl complex [Ru(II)-OH(2)](2+) (Ru = Ru complex with one 4-t-butyl-2,6-di-(1',8'-naphthyrid-2'-yl)-pyridine ligand and two 4-picoline ligands) has been carried out using electrochemistry, UV-vis and resonance Raman spectroscopy, pulse radiolysis, stopped flow, and electrospray ionization mass spectrometry (ESI-MS) with H(2)(18)O labeling experiments and theoretical calculations. The results reveal a number of intriguing properties of intermediates such as [Ru(IV)═O](2+) and [Ru(IV)-OO](2+). At pH > 2.9, two consecutive proton-coupled one-electron steps take place at the potential of the [Ru(III)-OH](2+)/[Ru(II)-OH(2)](2+) couple, which is equal to or higher than the potential of the [Ru(IV)═O](2+)/[Ru(III)-OH](2+) couple (i.e., the observation of a two-electron oxidation in cyclic voltammetry). At pH 1, the rate constant of the first one-electron oxidation by Ce(IV) is k(1) = 2 × 10(4) M(-1) s(-1). While pH-independent oxidation of [Ru(IV)═O](2+) takes place at 1420 mV vs NHE, bulk electrolysis of [Ru(II)-OH(2)](2+) at 1260 mV vs NHE at pH 1 (0.1 M triflic acid) and 1150 mV at pH 6 (10 mM sodium phosphate) yielded a red colored solution with a Coulomb count corresponding to a net four-electron oxidation. ESI-MS with labeling experiments clearly indicates that this species has an O-O bond. This species required an additional oxidation to liberate an oxygen molecule, and without any additional oxidant it completely decomposed slowly to form [Ru(II)-OOH](+) over 2 weeks. While there remains some conflicting evidence, we have assigned this species as (1)[Ru(IV)-η(2)-OO](2+) based on our electrochemical, spectroscopic, and theoretical observations alongside a previously reported analysis by T. J. Meyer's group (J. Am. Chem. Soc. 2010, 132, 1545-1557).     

杭州城区的自然季节和天气类型

本文以杭州城区气象台站的观测资料为依据,运用综合气候学方法,将杭州城区划分为11个自然季节和31种天气类型.     

Design of perylene-diimides-based small-molecules semiconductors for organic solar cells

A series of perylene-diimide-based small molecules have been designed to explore their optical, electronic and charge transport properties as organic solar cell materials. The frontier molecular orbitals analysis has turned out that the vertical electronic transitions of absorption are characterised as intramolecular charge transfer between perylene diimide moieties and substituent aromatic groups. Our results suggest that the optical and electronic properties and reorganisation energies are affected by the introduction of different aromatic groups to these molecules. The calculation results showed that the designed molecules own the large longest wavelength of absorption spectrum, the oscillator strength and absorption region values. On the basis of the investigated results, the designed molecules could be used as solar cell material with intense broad absorption spectra. Furthermore, they are expected to be the promising candidates for hole and/or electron transport materials.     

Observation of nitrogen-14, carbon-13 indirect spin-spin coupling in high-resolution 13C CP/MAS spectra of solids.

The 13C CP/MAS NMR spectrum of [(n-C3H7)4N][Cd(SCN)3], 1, indicates the presence of three non-equivalent thiocyanate ligands, in agreement with the results of a recent single-crystal X-ray diffraction study. Examination of the 13C MAS line shapes allows direct measurement of the indirect spin-spin coupling constants, 1J(14N, 13C) = 16 +/- 1 Hz and 2J(111/113Cd, 13C) = 75 +/- 5 Hz, for the unique N-bonded thiocyanate ligand. This is the first reported measurement of 1J(14N, 13C) and 2J(111/113Cd, 13C) in the solid state. Possible reasons for the failure to observe 1J(14N, 13C) values in previous high-resolution 13C CP/MAS NMR studies are summarized.     

Calcium tetraboride-does it exist? Synthesis and properties of a carbon-doped calcium tetraboride that is isotypic with the known rare earth tetraborides

Crystalline samples of carbon-doped CaB4 were synthesized by solid-state reactions in sealed niobium ampules from the elements Ca, B, and C. The structure was determined by single-crystal X-ray diffraction (P4/mbm, Z = 4, a = 7.0989(7) A, c = 4.1353(5) A, R1 = 0.026, and wR2 = 0.058) revealing an atom arrangement containing a three-dimensional boron network built up from B6 octahedra and B2 dumbbells which is well-known from the structures of rare earth tetraborides. Crystals of CaB(4-x)Cx are black with a metallic luster and behave stable against mineral acids. Band structure calculations indicate that CaB4 is a stable semiconducting compound with a narrow band gap and that carbon should not necessarily be required for the stability of this compound. The presence of carbon in the crystalline samples of CaB(4-x)Cx was indicated by electron energy loss spectroscopy, but the carbon content in the samples was estimated to be less than 5% according to inductively coupled plasma-atomic emission spectrometry measurements. The distribution of boron and carbon atoms in the structure was investigated by means of 11B and 13C solid-state magic angle spinning NMR. Measurements of the magnetic susceptibility indicate a temperature-independent paramagnetism down to 20 K.     

trans-[Ru(II)(dpp)Cl2]: a convenient reagent for the preparation of heteroleptic Ru(dpp) complexes, where dpp is 2,9-di(pyrid-2'-yl)-1,10-phenanthroline

The reaction of 2,9-di(pyrid-2'-yl)-1,10-phenanthroline (dpp) with [RuCl(3)·3H(2)O] or [Ru(DMSO)(4)Cl(2)] provides the reagent trans-[Ru(II)(dpp)Cl(2)] in yields of 98 and 89%, respectively. This reagent reacts with monodentate ligands L to replace the two axial chlorides, affording reasonable yields of a ruthenium(II) complex with dpp bound tetradentate in the equatorial plane. The photophysical and electrochemical properties of the tetradentate complexes are strongly influenced by the axial ligands with electron-donating character to stabilize the ruthenium(III) state, shifting the metal-to-ligand charge-transfer absorption to lower energy and decreasing the oxidation potential. When the precursor trans-[Ru(II)(dpp)Cl(2)] reacts with a bidentate (2,2'-bipyridine), tridentate (2,2';6,2'-terpyridine), or tetradentate (itself) ligand, a peripheral pyridine on dpp is displaced such that dpp binds as a tridentate. This situation is illustrated by an X-ray analysis of [Ru(dpp)(bpy)Cl](PF(6)).     

Molecular Ln(III)−H−E(II) Linkages (Ln=Y,Lu; E=Ge,Sn, Pb)

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH₃ and trivalent rare-earth-metallocene alkyls [Cp*₂Ln(CH{SiMe₃}₂)] gave complexes [Cp*₂Ln(μ-H)₂SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*₂Ln(μ-H)₂EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)₂] to the rare-earth-metal hydrides [(Cp*₂LnH)₂]. The lead compounds [Cp*₂Ln(μ-H)₂PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.