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81.
The crystal structures of two new ternary phases, La4Ag10Mg3 and La4Ag10.3Mg12, were refined from X-ray single crystal diffraction data. La4Ag10Mg3 crystallizes in the Ca4Au10In3 structure type, an ordered variant of the binary Zr7Ni10 compound: orthorhombic, Cmce, oS68, a=14.173(5), b=10.266(3), c=10.354(3) Å, Z=4, wR2=0.0826, 676 F2 values, 50 variables. La4Ag10.3Mg12 represents a new structure type: orthorhombic, Cmmm, oS116-10.32, a=9.6130(3), b=24.9663(8), c=9.6333(2) Å, Z=4, wR2=0.0403, 1185 F2 values, 101 variables. The structural analysis of both compounds, highlighting a significant contraction of the Ag-Mg distances, suggests the existence of three-dimensional [Ag-Mg] networks hosting La atoms. LMTO calculations applied to La4Ag10Mg3 indicate that the strongest bonds occur for Ag-Ag and Ag-Mg interactions, and confirm the presence of a 3D[Ag10Mg3]δ− polyanionic framework balanced by positively charged La atoms.  相似文献   
82.
Jenkins DM  Bernhard S 《Inorganic chemistry》2010,49(24):11297-11308
Presented is the synthesis and characterization of a series of luminescent heteroleptic bis-cyclometalated platinum(IV) complexes. An oxidation-facilitated cyclometalation is employed to convert platinum(II) pendant species into bis-cyclometalated platinum(IV) dichlorides, which are transformed into the tris-chelated diimine complexes through ligand substitution. The structure-property relationship is probed by judiciously varying substituents on both the C(∧)N and the N(∧)N ligands resulting in a family of complexes exhibiting blue emission, long excited-state lifetimes, and highly efficient oxygen quenching. Excited-state properties are corroborated by static and time-dependent density-functional theory calculations of both the singlet and the triplet state.  相似文献   
83.
A library of monodentate phosphane ligands, each bearing a guanidine receptor unit for carboxylates, was designed. Screening of the library gave some excellent catalysts for regioselective hydroformylation of β,γ‐unsaturated carboxylic acids. A terminal alkene, but‐3‐enoic acid, was hydroformylated with a linear/branched (l/b) regioselectivity up to 41. An internal alkene, pent‐3‐enoic acid was hydroformylated with regioselectivity up to 18:1. Further substrate selectivity (e.g., acid vs. methyl ester) and reaction site selectivity (monofunctionalization of 2‐vinylhept‐2‐enoic acid) were also achieved. Exploration of the structure–activity relationship and a practical and theoretical mechanistic study gave us an insight into the nature of the supramolecular guanidinium–carboxylate interaction within the catalytic system. This allowed us to identify a selective transition‐state stabilization by a secondary substrate–ligand interaction as the basis for catalyst activity and selectivity.  相似文献   
84.
The excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses. The excited-state reactions were identified in aqueous media as a function of the pH value. Apart from the well-known inversion of the ordinary dissociation properties of these compounds, new species were found which exist only in the excited-state resulting from a temporal and reversible annihilation of the aromatic bond system. These species and their reaction mechanisms were detected by their absorption and fluorescence spectra.  相似文献   
85.
A simple and reliable method for the determination of arsenic in sediment and in coal without sample digestion, based on hydride generation from slurry samples is proposed. After grinding the samples to a particle size of 50 μm, the sample powder was mixed with aqua regia and hydrofluoric acid in an ultrasonic bath for 30 min. After diluting the mixture with hydrochloric acid, the slurry was allowed to stand for 48 h, and an aliquot was used for hydride generation with sodium borohydride. More than 80% of the arsenic was leached to the aqueous phase under these conditions, except for one sediment sample with very high silica content. The generated arsine was collected in a graphite tube, treated with 0.5 mg of iridium as a permanent modifier, and the arsenic determination was carried out by electrothermal atomic absorption spectrometry. The same tube could be used for at least 160 cycles without any re-treatment. The greatest advantage of the method was that only a minimum of reagents and sample handling were required, reducing the risks of contamination and/or analyte loss. However, the addition calibration technique had to be used in order to obtain results within the 95% confidence level for 11 certified reference materials, 5 sediments, 5 coals and one coal fly ash. One certified sediment slurry was spiked with the analyte and the resulting addition calibration curve was used for the analysis of the certified sediments. Similarly, one certified coal was used to obtain the addition calibration curve for the coal and coal fly ash samples. The recoveries of the certified values, except for one sediment, were between 91 and 115%. The limits of detection in the samples were 0.54 and 0.7 μg g−1 for the coal and sediment samples, respectively, obtained for 1 ml of slurry containing 1 mg of sample.  相似文献   
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In molecular imaging, multimodal imaging agents can provide complementary information, for improving the accuracy of disease diagnosis or enhancing patient management. In particular, optical/nuclear imaging may find important preclinical and clinical applications. To simplify the preparation of dual‐labeled imaging agents, we prepared versatile monomolecular multimodal imaging probe (MOMIP) platforms containing both a fluorescent dye (BODIPY) and a metal chelator (polyazamacrocycle). One of the MOMIP was conjugated to a cyclopeptide (i.e., octreotide) and radiolabeled with 111In. In vitro and in vivo studies of the resulting bioconjugate were conducted, highlighting the potential of these BODIPY‐based bimodal probes. This work also confirmed that the biovector and/or the bimodal probes must be chosen carefully, due to the impact of the MOMIP on the overall properties of the resulting imaging agent.  相似文献   
88.
The syn dimer of cyclobutadiene (tricyclo[4.2.0.0(2.5)]octa-3,7-diene, TOD) is subjected to ionization under different conditions and the resulting species are probed by optical and ESR spectroscopy. By means of quantum chemical modelling of the potential energy surfaces and the optical spectra, it is possible to assign the different products that arise spontaneously after ionization or after subsequent warming or illumination of the samples. Based on these findings, we propose a mechanistic scheme which involves a partitioning of the incipient radical cation of TOD between two electronic states. These two states engage in (near) activation-less decay to the more stable valence isomers, cyclooctatetraene (COT*+) and a bis-cyclobutenylium radical cation BCB*+. The latter product undergoes further rearrangement, first to tetracyclo[4.2.0.0(2,4).0(3,5]oct-7-ene (TCO*+) and eventually to bicyclo[4.2.0]octa-2,4,7-triene (BOT*+) which can also be generated photochemically from BCB*+ or TCO*+. The surprising departure of syn-TOD*+ from the least-motion reaction path leading to BOT*+ can be traced to strong vibronic interactions (second-order Jahn-Teller effects) which prevail in both possible ground states of syn-TOD*+. Such effects seem to be more important in determining the intramolecular reactivity of radical cations than orbital or state symmetry rules.  相似文献   
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