Photoreduction of carbon dioxide to carbon monoxide with hydrogen catalyzed by a rhenium(i) phenanthroline-polyoxometalate hybrid complex

A phenanthroline ligand decorated at the 5,6-position with a 15-crown-5 ether was used to prepare a metalorganic-polyoxometalate hybrid complex Re(I)(L)(CO)(3)CH(3)CN-MHPW(12)O(40) (L = 15-crown-5-phenanthroline, M = Na(+), H(3)O(+)). X-ray diffraction, (1)H and (13)C NMR, ESI-MS, IR, and elemental analysis were used to characterize this complex. In the presence of Pt/C, the polyoxometalate moiety in Re(I)(L)(CO)(3)CH(3)CN-MHPW(12)O(40) can oxidize H(2) to two protons and two electrons which in the presence of visible light can catalyze the photoreduction of CO(2) to CO with H(2) as the reducing agent instead of the universally used amines as sacrificial reducing agents. An EPR spectrum of a stable intermediate species under reaction conditions shows characteristics of a PW(V)W(VI)(11)O(40) and a Re(0) species with a tentative assignment of the intermediate as Re(0)(L)(CO)(3)(S)-MH(3)PW(V)W(VI)(11)O(40).     

The Mechanical Role of Metal Ions in Biogenic Protein‐Based Materials

Protein‐metal interactions—traditionally regarded for roles in metabolic processes—are now known to enhance the performance of certain biogenic materials, influencing properties such as hardness, toughness, adhesion, and self‐healing. Design principles elucidated through thorough study of such materials are yielding vital insights for the design of biomimetic metallopolymers with industrial and biomedical applications. Recent advances in the understanding of the biological structure–function relationships are highlighted here with a specific focus on materials such as arthropod biting parts, mussel byssal threads, and sandcastle worm cement.     

Templating nanostructures by mesoporous materials with an emphasis on room temperature and cryogenic TEM studies

Rapid strides realized in the field of ordered mesoporous silica (OMS) with a well-defined pore shape and nanometric sizes, provide new gateways for the preparation of nanostructured materials having controlled shape and size with a very narrow distribution. The focus of the current review is on the synthesis of nanostructures templated by OMS either in bulk or in thin film form. The importance of electron microscopy as an indispensable technique in the structural characterization of OMS templated nanostructures, including cryo-TEM, electron tomography and HR-SEM, is highlighted in this review.     

Synthesis, structure, and reactivity of rhodium and iridium complexes of the chelating bis-sulfoxide tBuSOC2H4SOtBu. Selective O-H activation of 2-hydroxy-isopropyl-pyridine

The chloro-bridged rhodium and iridium complexes [M2(BTSE)2Cl2] (M = Rh 1, Ir 2) bearing the chelating bis-sulfoxide tBuSOC2H4SOtBu (BTSE) were prepared by the reaction of [M2(COE)4Cl2] (M = Rh, Ir; COE = cyclooctene) with an excess of a racemic mixture of the ligand. The cationic compounds [M(BTSE)2][PF6] (M = Rh 3, Ir 4), bearing one S- and one O-bonded sulfoxide, were also obtained in good yields. The chloro-bridges in 2 can be cleaved with 2-methyl-6-pyridinemethanol and 2-aminomethyl pyridine, resulting in the iridium(I) complexes [Ir(BTSE)(Py)(Cl)] (Py = 2-methyl-6-pyridinemethanol 5, 2-aminomethyl-pyridine 6). In case of the bulky 2-hydroxy- isopropyl-pyridine, selective OH oxidative addition took place, forming the Ir(III)-hydride [Ir(BTSE)(2-isopropoxy-pyridine)(H)(Cl)] 7, with no competition from the six properly oriented C-H bonds. The cationic rhodium(I) and iridium(I) compounds [M(BTSE)(2-aminomethyl-pyridine)][X] (M = Rh 8, Ir 10), [Rh(BTSE)(2-hydroxy- isopropyl-pyridine)][X] 9(stabilized by intramolecular hydrogen bonding), [Ir(BTSE)(pyridine)2][PF6] 12, [Ir(BTSE)(alpha-picoline)2][PF6] 13, and [Rh(BTSE)(1,10-phenanthroline)][PF6] 14 were prepared either by chloride abstraction from the dimeric precursors or by replacement of the labile oxygen bonded sulfoxide in 3 or 4. Complex 14 exhibits a dimeric structure in the solid state by pi-pi stacking of the phenanthroline ligands.     

Growth of Au/Ag nanowires in thin surfactant solution films: an electron microscopy study

The surfactant templated gold-silver nanowire growth process in a thin solution film was probed by cryo-transmission electron microscopy (cryo-TEM). The increasing surfactant concentration upon film drying appears to induce phase transformations in the film and form a liquid crystalline template for the nanowires growth. High-resolution transmission electron microscopy (HRTEM) and electron holography revealed that the nanowires were polycrystalline with some preferred crystallite orientations and had a roughly cylindrical cross-section. Further improvement of the technique may lead to highly ordered metal nanowire arrays within the surfactant matrix similar to the closely related mesoporous materials.     

Assessment of PHB with varying hydroxyvalerate content for potential packaging applications

Poly-(hydroxybutyrate) (PHB) is biodegradable aliphatic polyester that is produced by a wide range of microorganisms. Basic PHB has relatively high glass transition and melting temperatures. To improve flexibility for potential packaging applications, PHB is synthesized with various co-polymers such as poly-(3-hydroxyvalerate) (HV) leading to a decrease of the glass transitions and melting temperatures. In addition, the HV broadens the processing window since there is improved melt stability at lower processing temperatures. In this study, PHB synthesized with different valerate contents (5%, 12%, and 20%) and varying in molecular weights were characterized. All PHBV materials displayed a glass transition between −10 and 20 °C. The two melting transitions found for Aldrich 5%, 12%, and Tianan 20%, resulted from crystals formed during cooling of the samples. The complex viscosity decreased with increasing temperature due to a decrease in molecular weights of the samples. These results suggest that processing the co-polymer below 160 °C would be beneficial with low screw speed. The mechanical results indicate all PHBV materials had high elastic modulus and flexural strength with low tensile strength and elongation at break. The WVTR results indicated the polymer to be very hydrophilic, resulting in higher water transmission rates.     

Extent and mechanism of metal ion incorporation into precipitated ferrites

The ability of many noniron metals to be incorporated into the structure of ferrites is being utilized in numerous industrial and environmental applications. The incorporation of some of these metals during Fe(II) oxidation-induced precipitation at moderate temperatures (80-100°C) appears to be limited, for reasons not fully understood, and to extents not always agreed (e.g., Ni(2+), Cr(3+)). In this paper, the incorporation maxima of six metals into the structure of precipitated ferrites (in terms of x in Me(x)Fe(3-)(x)O(4), Me represents a noniron metal) were concluded to be 1.0, 1.0, 0.78, 0.49, 0.35, and 0.0 for Zn(2+), Co(2+), Ni(2+), Al(3+), Cd(2+) and Cr(3+), respectively. With the exception of the much larger Cd(2+), these values were associated with kinetic considerations controlled by the H(2)O exchange rate between the hydration shells surrounding the dissolved metal ion.     

Low-pressure hydrogenation of carbon dioxide catalyzed by an iron pincer complex exhibiting noble metal activity

A highly active iron catalyst for the hydrogenation of carbon dioxide and bicarbonates works under remarkably low pressures and achieves activities similar to some of the best noble metal catalysts. A mechanism is proposed involving the direct attack of an iron trans-dihydride on carbon dioxide, followed by ligand exchange and dihydrogen coordination.