Single atoms and few-atom clusters of platinum are uniformly installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and X-ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.

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A new high-temperature polymorph of 5-(4-pyridyl)tetrazole has been discovered and characterized using X-ray crystallography and terahertz (THz) spectroscopy. The THz spectrum of the new polymorph was compared to the previously published form and was replicated by means of solid-state density functional theory. Terahertz spectroscopy was used to determine the influence of the different packing motifs on the molecular and low energy lattice vibrations displayed in the region from 10 to 100 cm(-1). It was found that there is only a ∼2 cm(-1) difference in the primary peak location, caused by a whole molecule rotation along the principal a axis, between the two polymorphic forms. In addition, the energy of formation was determined, and it was found that the previously known polymorphic form is more stable by ∼0.25 kJ/mol, compared to the newly discovered form.

Organic photovoltaic devices promise low-cost, flexible options for future renewable energy that will reduce reliance on oil. Single-wall carbon nanotubes (SWCNTs) provide possibilities for increasing the efficiency of organic solar cells through increasing conductivity of composites used in such devices or through use as a charge acceptor in a bulk heterojunction device. We present data to indicate the physical interaction of SWCNTs with a conjugated polymer, poly[2'-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), on the basis of the spectroscopic assignments of various conformational species of different optical signature in N,N-dimethylacetamide (DMA) dispersions. We go on to show that energy transfer from nonaggregated MEH-PPV leads to enhanced SWCNT fluorescence in solutions of poorer solvent quality. Energy transfer from polymer chain lengths that are torsionally restricted is not observed. This would suggest that any electron transfer taking place is occurring through a concerted Dexter mechanism and that use of SWCNTs as an electron acceptor will likely have associated drawbacks.

Spin state is found to determine the mechanism and active site of catalytic hydrogenation on metal cation catalysts.

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