Three-dimensional modeling of performance degradation of planar SOFC with phosphine exposure
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Sezer, Hayri↗
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Epitaxial ZnGeP 2 Thin Films on Si and GaP by Reactive Combinatorial Sputtering in Phosphine
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36 MATERIALS SCIENCE↗
Phosphine Ligand Binding and Catalytic Activity of Group 10–14 Heterobimetallic Complexes
We report heterobimetallic complexes have attracted much interest due to their broad range of structures and reactivities as well as unique catalytic abilities. Additionally, these complexes can be utilized as single-source precursors for the synthesis of binary intermetallic compounds. An example is the family of bis(pyridine-2-thiolato)dichloro-germanium and tin complexes of group 10 metals (Pd and Pt). The reactivity of these heterobimetallic complexes is highly tunable through substitution of the group 14 element and the neutral ligand bound to the transition metal. Here, we study the binding energies of three different phosphorous-based ligands, PR 3 (R = Bu, Ph, and OPh) by density functional theory and restricted Hartree–Fock methods. The PR 3 ligand-binding energies follow the trend of PBu 3 > PPh 3 > P(OPh) 3 , in agreement with their sigma-bonding ability. These results are confirmed by ligand exchange experiments monitored with 31 P NMR spectroscopy, in which a weaker binding PR 3 ligand is replaced with a stronger one. Furthermore, we demonstrate that the heterobimetallic complexes are active catalysts in the Negishi coupling reaction, where stronger binding PR 3 ligands inhibit access to an active site at the metal center. Similar strategies could be applied to other complexes to better understand their ligand-binding energetics and predict their reactivity as both precursors and catalysts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Role of High-Spin Species and Pendant Amines in Electrocatalytic Alcohol Oxidation by a Nickel Phosphine Complex
We report the development of active and efficient electrocatalysts for oxidation of alcohols using earth-abundant metals will aid the progress towards a renewable energy economy. Here we present a detailed mechanistic study of electrocatalytic benzyl alcohol oxidation by a molecular nickel complex containing pendant amines using a combination of kinetic studies, NMR spectroscopy, and density functional theory. The catalyst preferentially binds alcohol in high-spin octahedral geometry, but this complex is not readily deprotonated by exogeneous base and inhibits catalysis. Dissociation of one or more solvent ligands returns the complex to a low-spin state that can be deprotonated. Kinetic modeling indicates the off-cycle high-spin intermediate lowers the catalytic turnover frequency by a factor of eight, suggesting that substantial gains in activity can be attained by improvements to the catalyst coordination geometry. In a second finding, we demonstrate the pendant amine of the catalyst only functions as a proton relay for the potential-determining step, oxidation of a nickel hydride intermediate, but does not have a substantial impact on the overall rate for oxidation of benzyl alcohol to benzaldehyde. This result contradicts the common expectation for pendant amines to participate in rate-limiting proton transfer reactions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
ESI-MS Identification of the Cationic Phosphine-Ligated Gold Clusters Au1-Au22: Insight into the Gold-Ligand Ratio and Abundance of Larger Clusters
Triphenylphosphine (PPh3)-ligated gold clusters offer promising potential applications due to their relative ease of synthesis and usefulness in forming advanced cluster architectures. While previous studies reported cationic PPh3-ligated gold clusters with core sizes of Au1 - Au4, Au6 - Au11, and Au¬13 - Au14, there has not been definitive identification by mass spectrometry of larger clusters in the Au12 - Au25¬ range. Herein, we survey a polydisperse solution of cationic PPh3-ligated gold clusters using high mass-resolution (M/?M = 60,000) electrospray ionization mass spectrometry (ESI-MS). To improve the sensitivity and mass resolution of larger clusters for unambiguous identification, we increased the number of scan averages and reduced the range of mass collection windows to 200 m/z, thereby mitigating potential mass and ion abundance bias resulting from smaller “building block” gold clusters and other solution components present in higher abundance. In addition to the previously reported clusters, we identified several new species including Au5(PPh3)5+, Au12(PPh3)9HCl2+, Au15(PPh3)9Cl2+, Au16(PPh3)10Cl22+, Au17(PPh3)113+, Au18(PPh3)102+, Au19(PPh3)10Cl2+, Au20(PPh3)12H33+, Au21(PPh3)10Cl2+, and Au22(PPh3)10Cl22+, indicating that a full range of clusters between Au1 - Au22 may be observed in a single polydisperse solution. Considering all of the observed clusters, our findings provide evidence that the “magic number” icosahedral Au13 may be the transition point in cluster growth between smaller clusters, exhibiting a 1:1 gold-to-ligand ratio, and larger clusters, wherein subsequent gold atoms are added to the core without an equal number of accompanying ligands. Our method demonstrates that reducing the range of m/z collection windows and increasing the number of scan averages can improve instrument sensitivity for cationic gold clusters and enable a more complete survey of polydisperse solutions, thereby providing new insights to guide and validate the results of other characterization methods and theoretical calculations. This work was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. MH acknowledges support from the DOE Science Undergraduate Laboratory Internship (SULI) program. HH acknowledges support from the DOE Office of Workforce Development for Teachers and Scientist (WDTS) under the Visiting Faculty Program (VFP). This work was performed using EMSL, a national scientific user facility sponsored by the DOE's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle.
Hewitt, Michael↗
Improving the theoretical description of Ln( iii )/An( iii ) separation with phosphinic acid ligands: a benchmarking study of structure and selectivity
Density functionals with high exact exchange ( E HFX ≥ 50%) show the best agreement with CCSD(T)-DKH2 Am( iii )/Eu( iii ) selectivities and MP2-DKH2 distances.
Chapleski, Robert C.↗
Synthesis, characterization, and theoretical analysis of a plutonyl phosphine oxide complex
The interplay of bond strength and covalency are examined in AnO 2 Cl 2 (OPcy 3 ) 2 (An = Pu, U) complexes. The synthesis of trans-PuO 2 Cl 2 (OPcy 3 ) 2 , 1-Pu, has been carried out and confirmed by single crystal X-ray diffraction along with UV-vis-NIR, and 31 P NMR spectroscopies. Theoretical analysis finds that despite a higher calculated covalency for the Pu–Cl interaction, the Pu–OPcy 3 interaction is stronger due to the accumulation of electron density in the interatomic region. As a result, the coordination of equatorial ligands slightly decreases the strength of the Pu≡O yl interactions relative to the free gas phase (PuO 2 ) 2+ ion.
Windorff, Cory J.↗
Gas-Phase Coordination of Phosphine-Chalcogenides to the Uranyl Cation
It is generally believed that actinides exhibit an increased covalency in bonding to soft-donor atoms such as nitrogen and sulfur compared to the lanthanides. The explanation is that the greater spatial extent of the 5f orbitals in the actinides compared to the 4f orbitals in the lanthanides accounts for this behavior. However, recent computational studies on lanthanide and actinide complexes with sulfur-donor atom ligands suggest that while calculated metrics of bond covalency could increase for actinide complexes with sulfur ligands, the overall stability of the complexes decreased. While many studies of actinide covalency were conducted in the condensed phases, this work investigates the intrinsic interaction between actinides and soft-donor ligands compared with oxygen in the gas phase.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Gas-Phase Coordination of Phosphine-Chalcogenides to the Uranyl Cation
It is generally believed that actinides exhibit an increased covalency in bonding to soft-donor atoms such as nitrogen and sulfur compared to the lanthanides. The explanation is that the greater spatial extent of the 5f orbitals in the actinides compared to the 4f orbitals in the lanthanides accounts for this behavior. However, recent computational studies on lanthanide and actinide complexes with sulfur-donor atom ligands suggest that while calculated metrics of bond covalency could increase for actinide complexes with sulfur ligands, the overall stability of the complexes decreased. While many studies of actinide covalency were conducted in the condensed phases, this work investigates the intrinsic interaction between actinides and soft-donor ligands compared with oxygen in the gas phase.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores
Ce-bastnäsite is the single largest mineral source for light rare-earth elements. In view of the growing industrial importance of rare-earth minerals, it is critical to develop more efficient methods for separating the valuable rare-earth-containing minerals from the surrounding gangue. In this work, we employ a combination of periodic density functional theory (DFT) and molecular mechanics (MM) calculations together with the de novo molecular design program HostDesigner to identify bis-phosphinate ligands that preferentially bind to the (100) Ce-bastnäsite surface rather than the (104) calcite surface. DFT calculations for a simple phosphinate ligand were employed to qualitatively understand key behaviors involved in ligand–metal, ligand–solvent, and solvent–metal interactions. These insights were then used to guide the search for flexible, rigid, and semirigid hydrocarbon linkers to identify candidate bis-phosphinate ligands with the potential to bind preferentially to Ce-bastnäsite. Among the five most promising bis-phosphinate ligands suggested by theoretical studies, three ligands were synthesized and their adsorption characteristics to bastnäsite (100) interfaces were characterized using vibrational sum-frequency (vSFG) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and isothermal titration calorimetry (ITC). The efficacy of the selective interfacial molecular binding was demonstrated by identifying a bis-phosphinate ligand capable of providing an overall higher surface coverage of alkyl groups relative to a monophosphinate ligand. The results highlight the interplay between adsorption binding strength and maximum surface coverage in determining ligand efficiency to render the mineral surface hydrophobic. DFT calculations further indicate that all tested ligands have higher affinity for Ce-bastnäsite than for calcite. Finally, this is consistent with the ITC data showing stronger adsorption enthalpy to bastnäsite than to calcite, making these ligands promising candidates for selective flotation of Ce-bastnäsite.
58 GEOSCIENCES↗