Boom in the West

Federal Reserve District, 12th ; Economic conditions - West (U.S.)

Weakening boom?

Federal Reserve District, 12th ; Economic conditions - West (U.S.)

Untangling the Web: The National Digital Libraries Initiative

A report on the National Digital Libraries Initiative is presented. To facilitate access to the vast resources of the Internet, the National Science Foundation has created the Digital Libraries Initiative. Several sites have come online recently that index and catalog materials in a way similar to a library, providing additional information about each site. The official National Science Digital Library Web site has the potential to become a one-stop site for a wide range of educational science material

Photoinduced One-Electron Reduction of Alkyl Halides by Dirhodium(II,II) Tetraformamidinates and a Related Complex with Visible Light

Various substituted dirhodium tetraformamidinate complexes, Rh(2)(R-form)(4) (R = p-CF(3), p-Cl, p-OCH(3), m-OCH(3); form = N,N\u27-diphenylformamidinate), and the new complex Rh(2)(tpgu)(4) (tpgu = 1,2,3-triphenylguanidinate) have been investigated as potential agents for the photoremediation of saturated halogenated aliphatic compounds, RX (R = alkyl group). The synthesis and characterization of the complexes is reported, and the crystal structure of Rh(2)(tpgu)(4) is presented. The lowest energy transition of the complexes is observed at approximately 870 nm and the complexes react with alkyl chlorides and alkyl bromides under low energy irradiation (lambda(irr) \u3e or = 795 nm), but not when kept in the dark. The metal-containing product of the photochemical reaction with RX (X = Cl, Br) is the corresponding mixed-valent Rh(2)(II,III)X (X = Cl, Br) complex, and the crystal structure of Rh(2)(p-OCH(3)-form)(4)Cl generated photochemically from the reaction of the corresponding Rh(2)(II,II) complex in CHCl(3) is presented. In addition, the product resulting from the dimerization of the alkyl fragment, R(2), is also formed during the reaction of each dirhodium complex with RX. A comparison of the dependence of the relative reaction rates on the reduction potentials of the alkyl halides and their C-X bond dissociation energies are consistent with an outer-sphere mechanism. In addition, the relative reaction rates of the metal complexes with CCl(4) decrease with the oxidation potential of the dirhodium compounds. The mechanism of the observed reactivity is discussed and compared to related systems

Tris(3-nitropentane-2,4-dionato-κ O,O′)-cobalt(III)

The structure of the title compound, [Co(C5H6NO4)3], consists of a CoIII ion octahedrally coordinated by three bidentate 3-nitro­pentane-2,4-dionate ligands. The complex was prepared via the nitration of tris­(2,4-penta­nedionato-κ2 O,O′)cobalt(III) with a solution of copper(II) nitrate in glacial acetic acid. The central C atom and the nitro group of one 3-nitro­pentane-2, 4-dionate ligand are disordered over two positions with an occupancy ratio of 0.848 (4):0.152 (4). A second nitro group is also disordered over two orientations with an occupancy ratio of 0.892 (7):0.108 (7). Two of the ligand methyl groups form C—H⋯O inter­actions with two different nitro groups to form chains running along the c axis. Additional C—H⋯O inter­actions are found between ligand methyl groups and the cobalt-bound O atoms, also resulting in the formation of chains along the c axis

Synthesis and Characterization of the Dimethyl-Substituted Bisbenzimidazole Ligand and Its Manganese Complex

Macrocycles with unique properties provide new avenues for the design of novel catalysts and materials. Here, we report, for the first time, the synthesis and characterization of the dimethyl-substituted bisbenzimidazole ligand (Me2BBZ) and its manganese complex (Mn-Me2BBZ). The Me2BBZ ligand is similar to porphyrin and phthalocyanine macrocycles in terms of its cavity size and metal-binding mode, but owing to electronic and charge differences, it exhibits properties that make it distinct from its structural counterparts. For instance, the optical spectra of bisbenzimidazoles lack transitions in the 500-900 nm region. Perhaps the most significant feature of the Me2BBZ ligand, however, is its inherent nonplanarity. Geometric restraints within this nonplanar ligand give rise to two atropisomers, which, when separated, could have potential in chiral catalysis and recognition. In addition, here we show that this nonplanarity can help to promote unusual crystal-packing interactions. Within the structure of the Mn-Me2BBZ complex, intermolecular pi-stacking interactions of the phenyl and benzimidazole groups lead to the formation of a distinct two-dimensional staircase lattice comprised of alternating Mn-Me2BBZ atropisomers. The potential significance of this structural arrangement is revealed by temperature-dependent magnetic studies that indicate weak antiferromagnetic coupling between the metal ions in the crystal. Fine-tuning of these long-range electronic and magnetic interactions could be useful for the design of novel molecular materials

Ground-State Properties and Excited-State Reactivity of 8-Quinolate Complexes of Ruthenium(II)

In an effort to explore new systems with highly reducing excited states, we prepared a series of Ru(II) complexes of the type Ru(L)(2)quo(+) (L = bpy (2,2\u27-bipyridine), phen (1,10-phenanthroline), dmphen (4,7-dimethyl-1,10-phenanthroline), tmphen (3,4,7,8-tetramethyl-1,10-phenanthroline); quo(-) = 8-quinolate) and investigated their photophysical and redox properties. The absorption and emission spectra of the Ru(L)(2)quo(+) are significantly red-shifted relative to those of the parent complexes Ru(L)(3)(2+), with emission maxima in the 757-783 nm range in water. The Ru(L)(2)quo(+) systems are easily oxidized with E(1/2)(Ru(III/II)) values ranging from +0.62 to +0.70 V vs NHE, making the emissive Ru --\u3e phen MLCT (metal-to-ligand charge transfer) excited states (E(00) approximately 1.95 eV in CH(3)CN) of the Ru(L)(2)quo(+) complexes significantly better reducing agents than the MLCT states of the parent Ru(L)(3)(2+) complexes. Emission lifetimes of 17.0 and 32.2 ns were measured for Ru(phen)(2)quo(+) in water and acetonitrile, respectively, and 11.4 ns for Ru(bpy)(2)quo(+) in water. Transient absorption results are consistent with the formation of reduced methyl viologen upon Ru(phen)(2)quo(+) excitation with visible light in water. The possibility of observing the Marcus inverted region in the forward bimolecular electron transfer reaction from the highly reducing Ru(phen)(2)quo(+) excited state was explored with neutral electron acceptors with reduction potentials ranging from +0.25 to -1.15 V vs NHE

Effect of intraligand π-delocalization on the photophysical properties of two new Ru(II) complexes

Two new Ru(II) complexes, [Ru(bpy)2(1-COO-iqu)]+ (2; bpy = 2,2_-bipyridine, 1-COO-iqu− = isoquinoline- 1-carboxylate) and [Ru(bpy)2(3-COO-iqu)]+ (3; 3-COO-iqu− = isoquinoline-3-carboxylate), were prepared and their crystal structures solved. The ground and excited state properties of 2 and 3 were characterized and compared to those of [Ru(bpy)3]2+ (1). The presence of the oxygen atom in the Ru(II) coordination sphere makes 2 and 3 easier to oxidize than 1. The Ru→bpy MLCT absorption and emission of 2 and 3 are red-shifted relative to that of 1 in CH2Cl2, and the E00 energies were estimated to be 1.89 eV and 1.95 eV from the low temperature emission of 2 and 3, resulting in excited state oxidation potentials of −1.03V and −1.10V vs SCE, respectively. In addition to the short-lived emissive 3MLCT state, a longlived species is observed in the transient absorption of 3 in DMSO (Ƭ=49μs) and pyridine (Ƭ =44μs), assigned to a solvent-coordinated complex. This intermediate is not observed for 3 in non-polar solvents or for 2. The absence of the solvent coordinated intermediate in 2 is explained by the stronger Ru–O bond afforded by the lower conjugation in that extends onto the carboxylic acid in the 1-COO-iquo−ligand, compared to that in the 3-COO-iqu−ligand in 3. Transient absorption experiments also show that the 3MLCT excited state of 3 is able to reduce methyl viologen

Bilateral Sudden Hearing Loss in Waldenstrom's Macroglobulinemia: MR Appearance

AbstractA 46 year-old man with acquired immunodeficiency syndrome presented with sudden development of vertigo and tinnitus and then simultaneous, bilateral, profound, sudden hearing loss. Magnetic resonance imaging showed bilateral high signal within the cochlea, vestibule, and portions of the semicircular canals on the non-enhanced T1-weighted images, most consistent with recent hemorrhage into the otic labyrinth. Serum analysis and bone-marrow biopsy led to diagnosis of Waldenstrom's macroglobulinemia – a likely cause of the presumed hemorrhage