Unusual Reactivity of Silicon Grease Towards Metal Alkoxides: Serendipity for Structural Chemistry

Controlled synthesis of moisture sensitive metal alkoxides demands the use of silicon grease for the inert synthetic manipulation of starting materials using glass apparatus to avoid adventitious hydrolysis. Spontaneous reaction of the siloxane units (-OSi(Me-3)(2))(n)) with the synthesized alkoxides often leads to molecular metal alkoxides based siloxane frameworks. These spontaneous incorporation of siloxane units into homo- and heterometallic alkoxide building blocks lead to the new multinuclear homo- and heterometallic alkoxide-siloxide compounds [Ce-2(OtBu)(4){Me2Si(OtBu)O}(2)(NO3)(2)] (1), [Zr{(OiPr)(2){Me2SiO2}Sr{Zr-2(OiPr)(8)}}(2)] (2) and [Sn2In2O2{Me2Si(OiPr)O}(OiPr)(5)](2) (3). Multifunctional coordination properties of these siloxane units enable the molecular approach to synthetically demanding polymetallic complexes for potential MOx-SiOx nanocomposites fabrication

Chemistry of Actinide Centers in Heterogeneous Catalytic Transformations of Small Molecules

The chemistry of actinide molecules and materials has shown remarkable conceptual advancements in the past decade illustrating their unique reactivity profiles, when compared with lanthanides and transition elements, but there are still some challenging questions on the intriguing stability of low valent states and the significant role of 5f orbitals in bonding and reactivity of actinides. The distinctive electronic flexibility of actinide centers makes them potential catalysts for heterogeneous molecular transformations because of the kinetic lability of their coordination states and facile switching among oxidaton states. Actinide-enabled chemical transformations such as the six-electron reduction of dinitrogen into two reactive ammonia molecules or four-electron oxidation of water into oxygen under mild conditions are promising pathways in the quest of high efficiency heterogeneous catalysts. This Review provides a comprehensive account on actinide-mediated catalytic transformation of small molecules such as CO, CO2, N-2, O-2, H2O, CH4, HCl, and NH3. The emphasis is placed on the emerging phenomena in actinide-based solid catalysts and controlled synthesis of nanostructured actinide materials as pristine and substrate-grown phases. The mechanistic investigations highlight the influence of the 5f electrons in multielectron transfer reactions and the propensity of actinide centers to achieve higher oxidation states that defines the surface termination in actinide oxides. Finally, the status and perspectives of actinide-containing materials beyond the nuclear fuel applications is discussed, underlining their exciting chemistry and unexplored potential toward alternative catalytic energy production processes

Unusual Reactivity of Silicon Grease Towards Metal Alkoxides: Serendipity for Structural Chemistry

Controlled synthesis of moisture sensitive metal alkoxides demands the use of silicon grease for the inert synthetic manipulation of starting materials using glass apparatus to avoid adventitious hydrolysis. Spontaneous reaction of the siloxane units (-OSi(Me-3)(2))(n)) with the synthesized alkoxides often leads to molecular metal alkoxides based siloxane frameworks. These spontaneous incorporation of siloxane units into homo- and heterometallic alkoxide building blocks lead to the new multinuclear homo- and heterometallic alkoxide-siloxide compounds [Ce-2(OtBu)(4){Me2Si(OtBu)O}(2)(NO3)(2)] (1), [Zr{(OiPr)(2){Me2SiO2}Sr{Zr-2(OiPr)(8)}}(2)] (2) and [Sn2In2O2{Me2Si(OiPr)O}(OiPr)(5)](2) (3). Multifunctional coordination properties of these siloxane units enable the molecular approach to synthetically demanding polymetallic complexes for potential MOx-SiOx nanocomposites fabrication

Synergistic Acceptor-Donor Interplay of Nd2Sn2O7 Pyrochlore based Sensor in Selective Detection of Hydrogen

Nanostructured thin film of Nd2Sn2O7 pyrochlore obtained by solution processing of a single molecular precursor with Nd-Sn ratio of 1:1 was found to show unprecedently high selectivity towards hydrogen sensing in the temperature range 200 degrees C-450 degrees C. Formation of crystalline Nd2Sn2O7 upon annealing the xerogel in air at 800 degrees C was confirmed by powder X-ray diffraction analysis. The heat-treated pyrochlore films exhibited a porous structure with interconnected grains confirmed by scanning electron microscope images. The gas sensing behavior of the device towards various analyte gases (H-2, CO, CH4, NO2, NH3) showed remarkably high selectivity towards H-2, while no sensor response against other reducing and oxidizing gases was monitored. The highest sensitivity towards H-2 was detected at 300 degrees C with a linear trend observed in the sensitivity values and H-2 concentration (5%-30%). Intercorrelated analysis of sensor characteristics, surface spectroscopy before and after hydrogen treatment and implications of unique crystallographic features of the pyrochlore lattice demonstrated a novel defined subsequent detection mechanism, which strongly differs from conventional binary oxides like SnO2. The significant increase in operating temperature upon H-2 exposure is apparently caused by the exothermic reaction between pyrochlore and molecular hydrogen to generate highly reactive hydride species during the detection mechanism. The high efficiency and reproducibility of the investigated sensor devices indicates the potential of Nd2Sn2O7 based sensors for hydrogen safety applications

Homo- and heteroleptic lanthanide-iron alkoxides as precursors in materials synthesis

Bimetallic iron-lanthanide alkoxides were synthesized by reacting [Ln{N(SiMe3)(2)}(3)] (Ln = Pr, Nd, Er) with [Fe-2((OBu)-Bu-t)(6)] in excess tert-butyl alcohol that triggered in-situ ligand exchange and Lewis acid-base interactions to form heterometallic compounds. Single crystal X-ray diffraction analyses of new compounds demonstrated that both Nd and Er containing compounds resulted in the formation of a hetero-bimetallic framework based on 1:1 Ln:Fe ratio, whereas higher Fe ratio (1:2) was observed when Pr was used as the rare earth metal, possibly due to its larger ionic radius (Pr(III): 0.99 angstrom). When the reaction was performed in the presence of chelating ligands (L: H-tfb-mea = N-(4,4,4-trifluorobut-1-en-3-on)-methoxyethyleneamine; H-2-tfb-en = N-N'-bis-(4,4,4-trifluorobut-1-en-3-on)-ethylenediamine), heteroleptic Ln-Fe derivatives were formed that were used in a representative case ([NdFe(L)((OBu)-Bu-t)(m)((HOBu)-Bu-t)]) as efficient precursor to synthesize nanocrystalline NdFeO3 ceramic

Magnetic Field-Assisted Chemical Vapor Deposition of UO2 Thin Films

Chemical vapor deposition (CVD) of UO2 thin films from in situ reductive decomposition using a U(VI) precursor ([U((OBu)-Bu-t)(6)]) was performed under applied magnetic fields (up to 1 T). The molecular mechanism responsible for the formation of U(IV) oxide was determined by nuclear magnetic resonance (NMR) analysis of gaseous byproducts revealed a reductive transformation of uranium hexakis-tert-butoxide into urania. Thin films were grown under zero-field and applied magnetic field conditions that clearly showed the guiding influence of the magnetic field on altering the morphology and crystallographic orientation of grains in UO2 deposits produced under an external magnetic field. Application of magnetic fields was found to reduce the grain size. Whereas films with a preferred orientation were observed under zero-field conditions, the application of magnetic fields (500 mT to 1 T) promoted a polycrystalline growth. X-ray photoelectron spectroscopy confirmed the formation of UO2 films with traces of U(VI) centers present on the surface, which was evidently due to the surface oxidation of coordinatively unsaturated U(IV) centers, which was found to be significantly reduced in the field-assisted process. These findings emphasize the positive effect of magnetic fields on controlling the texture and chemical homogeneity of CVD-grown films. The availability of a magnetic field as an extrinsic parameter for the CVD process adds to the conventional parameters, such as temperature, deposition time, and pressure, and expands the experimental space for thin-film growth

Controlled growth of Cu and CuOx thin films from subvalent copper precursors

A new Cu(I) precursor, [(COD)Cu(TFB-TFEA)] (COD = 1,5-cyclooctadiene and TFB-TFEA = N-(4,4,4-triftuorobut-1-en-3-on)-6,6,6-trifluoroethylamine) with high volatility and a clean thermal decomposition pattern was tested for thermal and plasma-assisted chemical vapor deposition (CVD). The heteroleptic configuration based on an anionic and a chelating neutral ligand unified both reactivity and sufficient stability resulting in an intrinsic molecular control over the composition of the resulting CVD deposits. The electronic influence of the ligand on the metal site was studied by 1D and 2D NMR spectroscopy, while El mass spectrometry revealed the ligand elimination cascade. Thermal and plasma CVD experiments demonstrated the suitability of the copper compound for an atom-efficient (high molecule-to-material yield) deposition of copper(0) and copper(I) oxide films that could be converted into crystalline copper(s) oxide upon heat treatment at 500 degrees C