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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO 2 reduction

Here, we prepared electron-rich derivatives of [Ir(tpy)(ppy)Cl] + with modification of the bidentate (ppy) or tridentate (tpy) ligands in attempt to increase the reactivity for CO 2 reduction and the ability to transfer hydrides (hydricity). Density functional theory (DFT) calculations reveal that complexes with dimethyl-substituted ppy have similar hydricities to the non-substituted parent complex, and photocatalytic CO 2 reduction studies show selective CO formation. Substitution of tpy for bis(benzimidazole)-phenyl or -pyridine (L3 and L4, respectively) induces changes in the physical properties much more pronounced than addition of methyl groups to ppy. Theoretical data predict [Ir(L3)(ppy)(H)] is the strongest hydride donor among complexes studied in this work, but [Ir(L3)(ppy)(NCCH 3 )] + cannot be reduced photochemically because the excited state reduction potential is only 0.52 V due to the negative ground state potential of –1.91 V. The excited state [Ir(L4)(ppy)(NCCH 3 )] 2+ is the strongest oxidant among complexes studied in this work and the singly reduced species is formed readily upon photolysis in the presence of tertiary amines. Both [Ir(L3)(ppy)(NCCH 3 )] + and [Ir(L4)(ppy)(NCCH 3 )] 2+ exhibit electrocatalytic current for CO 2 reduction. While a significantly greater overpotential is needed for the L3 complex, a small amount of formate (5-10 %) generation in addition to CO was observed as predicted by the DFT calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Long term stable deep red light-emitting electrochemical cells based on an emissive, rigid cationic Ir( iii ) complex

Here, the new cationic iridium complex [Ir(bzq) 2 (biq)][PF 6 ] (bzq = benzo[ h ]quinolinato and biq = 2,2'-biquinoline) has been synthesized for application as an emitter in light emitting electrochemical cells (LECs). The molecular structure and crystal packing of this complex were established by single X-ray diffraction (SXRD). The electrochemical and photophysical properties of the complex were examined to determine the frontier orbital energies as well as the optical transitions that led to photoemission. The complex was found to emit at 644 nm and 662 nm for powder and thin films, respectively. A high powder photoluminescence quantum yield of 25% was determined, which is attributed to a reduction in vibrational modes of the complex due to the use of the rigid cyclometalated (C^N) bzq ligand. A LEC with [Ir(bzq) 2 (biq)][PF 6 ] as the emitter was fabricated which showed a deep red emission (662 nm) with a luminance of 33.65 cd m –2 , yielding a current efficiency of 0.33 cd A –1 and a power efficiency of 0.2 lm W –1 . Most importantly, the LEC based on [Ir(bzq) 2 (biq)][PF 6 ] demonstrated a lifetime of 280 hours which is among the longest device lifetimes reported for any deep red light emitting LEC.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Mono- N -protected amino acid ligands stabilize dimeric palladium( II ) complexes of importance to C–H functionalization

Mono-protected amino acid (MPAA) ligands are used in a number of Pd-catalyzed C–H functionalization reactions. MPAAs have been proposed to bind to Pd( II ) via κ 2 -( N , O ) coordination, but such binding has not yet been experimentally validated. Herein, we report the synthesis and detailed characterization of a series of MPAA complexes prepared via cyclopalladation of dimethylbenzylamine in the presence of MPAAs. The isolated complexes exist as μ-carboxylato (MPAA) bridged dimers and feature potential M–M cooperativity and secondary sphere hydrogen bonding. Selective MPAA coordination and relay of stereochemistry, previously suggested to uniquely result from κ 2 -( N , O ) MPAA coordination, are both observed. The isolated MPAA complexes undergo C–C and C–X (X = Cl, Br, I) bond formation when treated with electrophiles used for catalytic C–H functionalization. Stoichiometric iodination of MPAA palladacycles was found to proceed via a dinuclear palladium species with one equivalent of iodine in the rate limiting transition structure, and the isolated complexes also served as viable precatalysts for catalytic C–H functionalization. Together, these results provide a number of insights into the reactivity of Pd-MPAA complexes relevant to C–H bond functionalization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Isolation of U(ii) compounds using strong donor ligands, C 5 Me 4 H and N(SiMe 3 ) 2 , including a three-coordinate U(ii) complex

New examples of uranium in the formal +2 oxidation state have been isolated by reduction of Cp tet 3 U (Cp tet = C 5 Me 4 H) and U(NR 2 ) 3 (R = SiMe 3 ) in the presence of 2.2.2-cryptand (crypt) to produce [K(crypt)][Cp tet 3 U] and [K(crypt)][U(NR 2 ) 3 ], respectively. Both complexes have properties consistent with 5f36d1 electron configurations and demonstrate that the U(II) ion can be isolated with electron donating ligands. The first discoveries of crystallographically-characterizable complexes of the new +2 ions of the rare-earth metals and the actinides involved complexes of three silyl-substituted cyclopentadienyl ligands like C 5 H 3 (SiMe 3 ) 2 (Cp") and C 5 H 4 SiMe 3 (Cp'),eqn (1). Complexes of +2 ions were also isolated with the tris(aryloxide) mesitylene ligand, [(Ad,MeArO) 3 mes] 3- , and with complexes containing two alkyl-substituted cyclopentadienyl ligands, C 5 H 3 (CMe 3 ) 2 (Cp tt ) and C 5 H 2 (CMe 3 ) 3 (Cp ttt ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A cyanide-bridged di-manganese carbonyl complex that photochemically reduces CO 2 to CO

Manganese(I) tricarbonyl complexes such as [Mn(bpy)(CO) 3 L] (L = Br, or CN) are known to be electrocatalysts for CO 2 reduction to CO. However, due to their rapid photodegradation under UV and visible light, these monomeric manganese complexes have not been considered as photocatalysts for CO 2 reduction without the use of a photosensitizer. We report a cyanide-bridged di-manganese complex, {[Mn(bpy)(CO) 3 ] 2 (μ-CN)}ClO 4 , which is both electrocatalytic and photochemically active for CO 2 reduction to CO. Compared to the [Mn(bpy)(CO) 3 CN] electrocatalyst, our CN-bridged binuclear complex is a more efficient electrocatalyst for CO 2 reduction using H 2 O as a proton source. In addition, we report a photochemical CO 2 reduction to CO using the dimanganese complex under 395 nm irradiation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Temperature dependence of the spin state and geometry in tricobalt paddlewheel complexes with halide axial ligands

Trinuclear cobalt paddlewheel complexes, [Co 3 (dpa) 4 X 2 ] (dpa = the anion of 2,2'-dipyridylamine, X = Cl–, Br–, –NCS–, –CN–, (NC) 2 N–), are known to demonstrate a thermally-induced spin-crossover (SCO). Despite a wealth of structural and magnetic information about such complexes, the role of the axial ligand on the characteristic SCO temperature (T 1/2 ) remains ambiguous. The situation is complicated by the observation that the solid state geometry of the complexes, symmetric or unsymmetric, with respect to the central cobalt ion, also appears to influence the SCO behavior. In order to seek trends in the relationship between the nature of the axial ligand, geometry and magnetic properties, we have prepared the first examples of tricobalt paddlewheel complexes with axial fluorido and iodido ligands, as well as two new chlorido and bromido solvates. Their SCO properties are discussed in the context of an examination of previously reported chlorido and bromido adducts. The main conclusions are: (1) T 1/2 values follow the trend I– < Br– ≈ Cl– < F–; (2) while the molecular geometry is predominantly guided by crystal packing for the Cl–, Br– and I– derivatives, the presence of an axial fluoride may favor a more symmetric core; (3) the magnetic characterization of a second example of an unsymmetric complex supports the observation that they display dramatically lower T 1/2 values than their symmetric analogues; and (4) SCO in crystallographically symmetric compounds apparently occurs without loss of molecular or crystallographic symmetry, while a gradual geometric transformation linking the temperature dependence of quasi-symmetric to unsymmetric in crystallographically unconstrained compounds was found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Evaluating the impacts of amino acids in the second and outer coordination spheres of Rh-bis(diphosphine) complexes for CO 2 hydrogenation

To explore the influence of a biologically inspired second and outer coordination sphere on Rh-bis(diphosphine) CO 2 hydrogenation catalysts, a series of five complexes were prepared by varying the substituents on the pendant amine in the P(Et) 2 CH 2 N R CH 2 P(Et) 2 ligands (P Et N R P Et ), where R consists of methyl ester modified amino acids, including three neutral (glycine methyl ester (GlyOMe), leucine methyl ester (LeuOMe), and phenylalanine methyl ester (PheOMe)), one acidic (aspartic acid dimethyl ester (AspOMe)) and one basic (histidine methyl ester (MeHisOMe)) amino acid esters. The turnover frequencies (TOFs) for CO 2 hydrogenation for each of these complexes were compared to those of the non-amino acid containing [Rh(depp) 2 ] + (depp) and [Rh(P Et N Me P Et ) 2 ] + (NMe) complexes. Each complex is catalytically active for CO 2 hydrogenation to formate under mild conditions in THF. Catalytic activity spanned a factor of four, with the most active species being the NMe catalyst, while the slowest were the GlyOMe and the AspOMe complexes. Finally, when compared to a similar set of catalysts with phenyl-substituted phosphorous groups, a clear contribution of the outer coordination sphere is seen for this family of CO 2 hydrogenation catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Bimetallic nickel-lutetium complexes: tuning the properties and catalytic hydrogenation activity of the Ni site by varying the Lu coordination environment

We present three heterobimetallic complexes containing an isostructural nickel center and a lutetium ion in varying coordination environments. The bidentate i Pr 2 PCH 2 NHPh and nonadentate ( i Pr 2 PCH 2 NHAr) 3 tacn ligands were used to prepare the Lu metalloligands, Lu( i Pr 2 PCH 2 NPh) 3 (1) and Lu{( i Pr 2 PCH 2 NAr) 3 tacn} (2), respectively. Reaction of Ni(COD) 2 (where COD is 1,5-cyclooctadiene) and 1 afforded NiLu( i Pr 2 PCH 2 NPh) 3 (3), with a Lu coordination number (CN) of 4 and a Ni–Lu distance, d(Ni–Lu), of 2.4644(2) Å. Complex 3 can further bind THF to form 3-THF, increasing both the Lu CN to 5 and d(Ni–Lu) to 2.5989(4) Å. On the other hand, incorporation of Ni(0) into 2 provides NiLu{( i Pr 2 PCH 2 NAr) 3 tacn} (4), in which the Lu coordination environment is more saturated (CN = 6), and the d(Ni–Lu) is substantially elongated at 2.9771(5) Å. Cyclic voltammetry of the three Ni–Lu complexes shows an overall ~410 mV shift in the Ni(0/I) redox couple, suggesting tunability of the Ni electronics across the series. Computational studies reveal polarized bonding interactions between the Ni 3d z 2 (major) and the Lu 5d z 2 (minor) orbitals, where the percentage of Lu character increases in the order: 4 (6.0% Lu 5d z 2 ) < 3-THF (8.5%) < 3 (9.3%). All three Ni–Lu complexes bind H 2 at low temperatures (-30 to -80 °C) and are competent catalysts for styrene hydrogenation. Complex 3 outperforms 4 with a four-fold faster rate. Additionally, adding increasing THF equivalents to 3, which would favor build-up of 3-THF, decreases the rate. We propose that altering the coordination sphere of the Lu support can influence the resulting properties and catalytic activity of the active Ni(0) metal center.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Mn IV -Oxo complex of a bis(benzimidazolyl)-containing N5 ligand reveals different reactivity trends for Mn IV -oxo than Fe IV -oxo species

Using the pentadentate ligand (N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine, 2pyN2B), presenting two pyridyl and two (N-methyl)benzimidazolyl donor moieties in addition to a central tertiary amine, new Mn II and Mn IV -oxo complexes were generated and characterized. The [Mn IV (O)(2pyN2B)] 2+ complex showed spectroscopic signatures (i.e., electronic absorption band maxima and intensities, EPR signals, and Mn K-edge X-ray absorption edge and near-edge data) similar to those observed for other MnIV-oxo complexes with neutral, pentadentate N 5 supporting ligands. The near-IR electronic absorption band maximum of [Mn IV (O)(2pyN2B)] 2+ , as well as DFT-computed metric parameters, are consistent with the equatorial (N-methyl)benzimidazolyl ligands being stronger donors to the MnIV center than the pyridyl and quinolinyl ligands found in analogous MnIV-oxo complexes. The hydrogen- and oxygen-atom transfer reactivities of [Mn IV (O)(2pyN2B)] 2+ were assessed through reactions with hydrocarbons and thioanisole, respectively. When compared with related Mn IV -oxo adducts, [Mn IV (O)(2pyN2B)] 2+ showed muted reactivity in hydrogen-atom transfer reactions with hydrocarbons. This result stands in contrast to observations for the analogous Fe IV -oxo complexes, where [Fe IV (O)(2pyN2B)] 2+ was found to be one of the more reactive members of its class.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis of homoleptic, divalent lanthanide (Sm, Eu) complexes via oxidative transmetallation

The direct synthesis of neutral, divalent samarium and europium complexes supported by the bulky bis(tris-tert-butoxysilyl)amide (BTTSA) ligand via oxidative transmetallation is reported. Through the use of a copper(I) ligand complex, conventional lanthanide halide starting materials for complex formation are circumvented and the clean formation of divalent complexes is achieved directly from the bulk metal. The structures of the [Ln(BTTSA) 2 ] (Ln = Sm, Eu) complexes are isotypic, presenting divalent lanthanide ions with distorted, six-coordinate geometries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

2.2.2-Cryptand complexes of neptunium(III) and plutonium(III)

New coordination environments are reported for Np(III) and Pu(III) based on pilot studies of U(III) in 2.2.2-cryptand (crypt). The U(III)-in-crypt complex, [U(crypt)I 2 ][I], obtained from the reaction between UI 3 and crypt, is treated with Me 3 SiOTf (OTf = O 3 SCF 3 ) in benzene to form the [U(crypt)(OTf) 2 ][OTf] complex. Similarly, the isomorphous Np(III) and Pu(III) complexes were obtained similarly starting from [AnI 3 (THF) 4 ]. All three complexes (1-An; An = U, Np, Pu) contain an encapsulated actinide in a THF-soluble complex. Finally, absorption spectroscopy and DFT calculations are consistent with 5f 3 U(III), 5f 4 Np(III), and 5f 5 Pu(III) electron configurations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Gaseous cyclodextrin- closo -dodecaborate complexes χCD·B 12 X 12 2– (χ = α, β, and γ; X = F, Cl, Br, and I): electronic structures and intramolecular interactions

A fundamental understanding of cyclodextrin- closo -dodecaborate inclusion complexes is of great interest in supramolecular chemistry. Herein, we report a systematic investigation on the electronic structures and intramolecular interactions of perhalogenated closo -dodecaborate dianions B 12 X 12 2– (X = F, Cl, Br and I) binding to α-, β-, and γ-cyclodextrins (CDs) in the gas phase using combined negative ion photoelectron spectroscopy (NIPES) and density functional theory (DFT) calculations. The vertical detachment energy (VDE) of each complex and electronic stabilization of each dianion due to the CD binding (ΔVDE, relative to the corresponding isolated B 12 X 12 2– ) are determined from the experiments along α-, β- and γ-CD in the form of VDE (ΔVDE): 4.00 (2.10), 4.33 (2.43), and 4.30 (2.40) eV in X = F; 4.09 (1.14), 4.64 (1.69), and 4.69 (1.74) eV in X = Cl; 4.11 (0.91), 4.58 (1.38), and 4.70 (1.50) eV in X = Br; and 3.54 (0.74), 3.88 (1.08), and 4.05 (1.25) eV in X = I, respectively. All complexes have significantly higher VDEs than the corresponding isolated dodecaborate dianions with ΔVDE spanning from 0.74 eV at (α, I) to 2.43 eV at (β, F), sensitive to both host CD size and guest substituent X. DFT-optimized complex structures indicate that all B 12 X 12 2– prefer binding to the wide openings of CDs with the insertion depth and binding motif strongly dependent on the CD size and halogen X. Dodecaborate anions with heavy halogens, i.e. , X = Cl, Br, and I, are found outside of α-CD, while B 12 F 12 2– is completely wrapped by γ-CD. Partial embedment of B 12 X 12 2– into CDs is observed for the other complexes via multipronged B–X … H–O/C interlocking patterns. The simulated spectra based on the density of states agree well with those of the experiments and the calculated VDEs well reproduce the experimental trends. Molecular orbital analyses suggest that the spectral features at low binding energies originated from electrons detached from the dodecaborate dianion, while those at higher binding energies are derived from electron detachment from CDs. Energy decomposition analyses reveal that the electrostatic interaction plays a dominating role in contributing to the host–guest interactions for the X = F series partially due to the formation of a O/C–H … X–B hydrogen bonding network, and the dispersion forces gradually become important with the increase of halogen size.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Near-infrared C-term MCD spectroscopy of octahedral uranium (V) complexes

C-term magnetic circular dichroism (MCD) spectroscopy is a powerful method for probing d–d and f–f transitions in paramagnetic metal complexes. However, this technique remains underdeveloped both experimentally and theoretically for studies of U(V) complexes of Oh symmetry, which have been of longstanding interest for probing electronic structure, bonding, and covalency in 5f systems. In this study, C-term NIR MCD of the Laporte forbidden f–f transitions of [UCl 6 ] - and [UF 6 ] - are reported, demonstrating the significant fine structure resolution possible with this technique including for the low energy Γ 7 → Γ 8 transitions in [UF 6 ] - . The experimental NIR MCD studies were further extended to [U(OC 6 F 5 ) 6 ] - , [U(CH 2 SiMe 3 ) 6 ] - , and [U(NC(tBu)(Ph)) 6 ] - to evaluate the effects of ligand-type on the f–f MCD fine structure features. Theoretical calculations were conducted to determine the Laporte forbidden f–f transitions and their MCD intensity experimentally observed in the NIR spectra of the U(V) hexahalide complexes, via the inclusion of vibronic coupling, to better understand the underlying spectral fine structure features for these complexes. These spectra and simulations provide an important platform for the application of MCD spectroscopy to this widely studied class of U(V) complexes and identify areas for continued theoretical development.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

Addition of [UI 2 (THF) 3 (μ-OMe)] 2 ·THF (2·THF) to THF solutions containing 6 equiv. of K[C 14 H 10 ] generates the heteroleptic dimeric complexes [K(18-crown-6)(THF) 2 ] 2 [U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)] 2 ·4THF (1 18C6 ·4THF) and {[K(THF) 3 ][U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)]} 2 (1 THF ) upon crystallization of the products in THF in the presence or absence of 18-crown-6, respectively. Both 1 18C6 ·4THF and 1 THF are thermally stable in the solid-state at room temperature; however, after crystallization, they become insoluble in THF or DME solutions and instead gradually decompose upon standing. X-ray diffraction analysis reveals 1 18C6 ·4THF and 1 THF to be structurally similar, possessing uranium centres sandwiched between bent anthracenide ligands of mixed tetrahapto and hexahapto ligation modes. Yet, the two complexes are distinguished by the close contact potassium-arenide ion pairing that is seen in 1 THF but absent in 1 18C6 ·4THF, which is observed to have a significant effect on the electronic characteristics of the two complexes. Structural analysis, SQUID magnetometry data, XANES spectral characterization, and computational analyses are generally consistent with U(IV) formal assignments for the metal centres in both 1 18C6 ·4THF and 1 THF , though noticeable differences are detected between the two species. For instance, the effective magnetic moment of 1 THF (3.74 μ B ) is significantly lower than that of 1 18C6 ·4THF (4.40 μ B ) at 300 K. Furthermore, the XANES data shows the U L III -edge absorption energy for 1 THF to be 0.9 eV higher than that of 1 18C6 ·4THF, suggestive of more oxidized metal centres in the former. Of note, CASSCF calculations on the model complex {[U(η 6 -C 14 H 10 )(η 4 -C 14 H 10 )(μ-OMe)] 2 } 2– (1*) shows highly polarized uranium–arenide interactions defined by π-type bonds where the metal contributions are primarily comprised by the 6d-orbitals (7.3 ± 0.6%) with minor participation from the 5f-orbitals (1.5 ± 0.5%). These unique complexes provide new insights into actinide–arenide bonding interactions and show the sensitivity of the electronic structures of the uranium atoms to coordination sphere effects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

nn-PINNs: Non-Newtonian physics-informed neural networks for complex fluid modeling

Time- and rate-dependent material functions in non-Newtonian fluids in response to different deformation fields pose a challenge in integrating different constitutive models into conventional computational fluid dynamic platforms. Considering their relevance in many industrial and natural settings alike, robust data-driven frameworks that enable accurate modeling of these complex fluids are of great interest. The main goal is to solve the coupled Partial Differential Equations (PDEs) consisting of the constitutive equations that relate the shear stress to the deformation and fully capture the behavior of the fluid under various flow protocols with different boundary conditions. Here, in this work, we present non-Newtonian physics-informed neural networks (nn-PINNs) for solving systems of coupled PDEs adopted for complex fluid flow modeling. The proposed nn-PINN method is employed to solve the constitutive models in conjunction with conservation of mass and momentum by benefiting from Automatic Differentiation (AD) in neural networks, hence avoiding the mesh generation step. nn-PINNs are tested for a number of different complex fluids with different constitutive models and for several flow protocols. These include a range of Generalized Newtonian Fluid (GNF) empirical constitutive models, as well as some phenomenological models with memory effects and thixotropic timescales. nn-PINNs are found to obtain the correct solution of complex fluids in spatiotemporal domains with good accuracy compared to the ground truth solution. We also present applications of nn-PINNs for complex fluid modeling problems with unknown boundary conditions on the surface, and show that our approach can successfully recover the velocity and stress fields across the domain, including the boundaries, given some sparse velocity measurements.

42 ENGINEERING↗
DOE OSTI2025

Dicopper( i ) complexes of a binucleating, dianionic, naphthyridine bis(amide) ligand

The dinucleating ligand, 1,8-naphthyridine-2,7-bis(2,6-diisopropylphenyl)carboxamide (NBDA), was synthesized by palladium-catalyzed aminocarbonylation. This ligand was treated with two equivalents of mesitylcopper(I) in the presence of [nBu4N]X (X = Cl, N3) to give the anionic complexes [nBu4N][Cu2(NBDA)(μ-Cl)] and [nBu4N][Cu2(NBDA)(μ-N3)]. Treatment of H2NBDA with mesitylcopper(I) and two equivalents of xylyl isocyanide led to the formation of a charge-neutral dicopper(I) complex, [Cu2(NBDA)(CNXyl)2], displaying two isocyanide ligands, each terminally bound to one of the copper atoms. The complexes were characterized by NMR and IR spectroscopy, as well as by single-crystal X-ray diffraction analysis. Electrochemical characterization of the complexes using cyclic voltammetry revealed a reversible ligand-based reduction between -1.65 and -2.0 V vs. Fc/Fc+. DFT calculations suggest a more ionic bonding character and weaker Cu-Cu interactions in the NBDA complexes compared to those with other 1,8-naphthyridine-based ligands. This is congruent with intermetallic separations of over 3 Å induced by relatively strong coordination of the copper atoms to the amide nitrogen donor atoms observed in the solid state molecular structures.

Sévery, Laurent↗
DOE OSTI2012

Positron annihilation studies of fluorine-vacancy complexes in Si and SiGe

The formation of fluorine-vacancy (FV) complexes in strained Si-SiGe-Si multilayer structures and relaxed SiGe layers of varying Ge content has been investigated using variable-energy positron annihilation spectroscopy, including Doppler-broadened spectra ratio curves. It has been found that in all sample types there are two distinct regions defined only by the damage created by the implanted F ions. The first, shallower region (from the surface to a depth of {approx}200 nm) was found to contain a mixture of undecorated vacancies and FV complexes; there is no correlation between the vacancy or F concentration in this region and the Ge content. The multi-layer samples may also have O contamination that is not present in the relaxed samples. The second region (at depths {approx}200-440 nm) contains primarily FV complexes in all samples. In the multi-layer samples secondary ion mass spectrometry (SIMS) results show peaks of F accumulating in, or at the interfaces of, each SiGe multi-layer; the FV complexes, however, are distributed over depths similar to those in the relaxed samples, with some localization at the SiGe layer located within the second region. The positron response is primarily to FV complexes formed by the F implant in all samples. The F: FV ratios are approximately 3-7: 1 in the relaxed samples. Positrons appear to be relatively insensitive to the largest of the F SIMS peaks which lies beyond the second region. This is probably because the F has filled all the open volume at the SiGe layer, leaving no positron trapping sites.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Correlation between oxygen adsorption energy and electronic structure of transition metal macrocyclic complexes

Oxygen adsorption energy is directly relevant to the catalytic activity of electrocatalysts for oxygen reduction reaction (ORR). In this study, we established the correlation between the O{sub 2} adsorption energy and the electronic structure of transition metal macrocyclic complexes which exhibit activity for ORR. To this end, we have predicted the molecular and electronic structures of a series of transition metal macrocyclic complexes with planar N{sub 4} chelation, as well as the molecular and electronic structures for the O{sub 2} adsorption on these macrocyclic molecules, using the density functional theory calculation method. We found that the calculated adsorption energy of O{sub 2} on the transition metal macrocyclic complexes was linearly related to the average position (relative to the lowest unoccupied molecular orbital of the macrocyclic complexes) of the non-bonding d orbitals (d{sub z{sup 2}}, d{sub xy}, d{sub xz}, and d{sub yz}) which belong to the central transition metal atom. Importantly, our results suggest that varying the energy level of the non-bonding d orbitals through changing the central transition metal atom and/or peripheral ligand groups could be an effective way to tuning their O{sub 2} adsorption energy for enhancing the ORR activity of transition metal macrocyclic complex catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗