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DOE OSTI2024

Effects of Structural Constraints on Excited-State Properties in Dimeric Cu(I) Diimine Complexes

Copper(I) bis-diimine complexes have played important roles in light-activated processes that can lead to their potential applications in photocatalysis and chemical sensing. Their metal-to-ligand charge-transfer (MLCT) excited-state properties are tunable by various structural factors. Dimeric Cu(I) complexes with connecting diimine derivative ligands offer another structural tuning platform for the excited-state properties. Here, we investigate excited-state properties in two covalently connected dimeric Cu(I)'s with varying structural constraints exerted by the number of carbons in the polyethylene bridge (C0 and C4) connecting the two copper(I) diimine moieties. An interesting feature of Cu(I) diimine complexes is their ability to flatten following a photoinduced structural change. Herein, we observe larger structural constraints and more structural rearrangement required upon excitation of the longer bridged complex C4 to achieve a conformation toward a more flattened tetrahedral coordination geometry compared to the shorter bridged C0. Vibrational wavepacket analysis of these complexes further supports the effect of these structural constraints where we observe a more rapid dephasing of the C0 complex, as opposed to the C4 complex, despite similar normal mode vibrations. The experimental results were supplemented by TDDFT calculations. In conclusion, the studies provide insight into using metal-metal interactions through constraints to tune excited-state dynamics and pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Probing the Framework Metal Dependent Properties of Actinide-Centered Polyoxoalkoxide Sandwich-Type Complexes

Development of a simple and scalable synthesis of (TBA) 3 [W 5 O 18 MoNO] provides for the formation of the mixed-metal lacunary polyoxoalkoxide, (TBA) 2 [W 4 O 13 (OMe) 4 MoNO][Na(MeOH)]. This complex was used to synthesize a series of polyoxoalkoxide sandwich-type complexes with the general formula (TBA) 2 [M{W 4 O 13 (OMe) 4 MoNO} 2 ], where M = Zr(IV), Hf(IV), Th(IV), U(IV), and Np(IV). Compared to the analogous all-molybdenum complexes, the series have drastically different optical and redox properties. The results indicate that framework metal substitution acts as a tool for “orbital engineering”, with Density Functional Theory (DFT) calculations revealing that the major consequence of incorporation of tungsten into the complexes is localization of LUMO and LUMO+1 on the molybdenum centers remaining in the molecule. The change in the distribution of the frontier orbitals translates to discrepancies in the electronic properties of the series. Given the rarity of polyoxometalate complexes featuring a U(V) ion, one electron oxidation of (TBA) 2 [U(IV){W 4 O 13 (OMe) 4 MoNO} 2 ] was pursued. Isolation of the corresponding U(V) centered sandwich-type complex is reported, only the second example of U(V)-polyoxometalate complex described to date.

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

Thermodynamic, Spectroscopic, and Computational Studies of f -Element Complexation by N -Hydroxyethyl-diethylenetriamine- N,N ', N ", N "-tetraacetic Acid

Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N',N",N"-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H + /Na + )ClO 4 . UV–vis spectroscopy was used to determine stability constants for Nd 3+ and Am 3+ complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal–nitrogen bond. This bond elongation is reflected in HEDTTA’s ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by ~3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid–liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N',N'-triacetic acid (HEDTA). The results presented here indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2026

Synthesis and Reactivity of Heteroleptic U 4+ Alkyl, Benzyl, and Hydride Imidophosphorane Complexes

A series of heteroleptic U 4+ benzyl, neopentyl, and methyl complexes supported by the imidophosphorane ligand, [N = P(N,N′-ditert-butylethylenediamide)(diethylamide)] 1− (NP*), were synthesized from the monoiodide precursor, [UI(NP*) 3 ]. These heteroleptic complexes were synthesized through the selective formation of [UI(NP*) 3 ] under transmetalation conditions in the reaction between [UI 4 (1,4-dioxane) 2 ] and K[NP*]. Formation of the homoleptic complex [U(NP*) 4 ] was not observed even in the presence of excess K[NP*]. The oxidation and hydrogenolysis reactivity of the neopentyl complex, [U(Npt)- (NP*) 3 ] (Npt = neopentyl) was explored. While cyclic voltammetry indicates a potentially isolable U5+ alkyl cation, chemical oxidation of the neopentyl complex results in the isolation of a cationic U 4+ complex with a bound diethyl ether in the primary coordination sphere, [U4+(NP*)) 3 (Et 2 O)][(BArF 24 )] (BArF 24 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate). Notably, hydrogenolysis of [U(Npt)(NP*) 3 ] with H2 gas at −20 °C results in the formation of a terminal hydride intermediate confirmed by in situ NMR spectroscopy and deuterium labeling with D 2 . The connectivity and structural parameters of this hydride intermediate, [UH(NP*) 3 ], which rapidly thermally decomposes to the homoleptic complex, [U(NP*) 4 ], can be confirmed by single-crystal X-ray diffraction studies of a crystal grown by chilling the reaction mixture. The identity of [U(NP*) 4 ] was confirmed by its direct, bulk synthesis from [U(Me)(NP*) 3 ] and HNP* in a protonolysis reaction.

Alkyls↗
DOE OSTI2017

Spectroscopic and Computational Studies of Spin States of Iron(IV) Nitrido and Imido Complexes

High-oxidation state metal complexes with multiply bonded ligands are of great interest for both their reactivity as well as their fundamental bonding properties. This paper reports a combined spectroscopic and theoretical investigation into the effect of the apical multiply bonded ligand on the spin state preferences of three-fold symmetric iron(IV) complexes with tris(carbene) donor ligands. Specifically, singlet (S = 0) nitrido [{PhB(Im R ) 3 }FeN], R = t Bu (1), Mes (mesityl, 2) and the related triplet (S = 1) imido complexes, [{PhB(Im R ) 3 }Fe(NR')] + , R = Mes, R' = Ad (1- adamantyl, 3), t Bu (4), have been investigated by electronic absorption and Mössbauer effect spectroscopies. For comparison, two other Fe(IV) nitrido complexes, [(TIMEN Ar )FeN] + , (TIMEN Ar = tris[2-(3-aryl-imidazol-2-ylidene)ethyl]amine; Ar = Xyl (xylyl), Mes), have been investigated by 57 Fe Mössbauer spectroscopy, including applied-field measurements. The paramagnetic imido complexes 3 and 4 were also studied by magnetic susceptibility measurements (for 3) and paramagnetic resonance spectroscopy: high-frequency and -field electron paramagnetic resonance (HFEPR) (for 3 and 4) and frequency-domain Fouriertransform (FD-FT) THz EPR (for 3), which reveal their zero-field splitting (zfs) parameters. Experimentally correlated theoretical studies comprising ligand-field theory (LFT) and quantum chemical theory (QCT), the latter including both density functional theory (DFT) and ab initio methods reveal the key role played by the Fe3 d z 2 (a1) orbital in these systems: the nature of its interaction with the nitrido or imido ligand dictates the spin state preference of the complex. Lastly, the ability to tune the spin state through the energy and nature of a single orbital has general relevance to the factors controlling spin states in complexes with applicability as single molecule devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Force-Modulated C–C Reductive Elimination from Nickel Bis(polyfluorophenyl) Complexes

We have analyzed the rate of C(sp 2 )–C(sp 2 ) reductive elimination from nickel(II) bis(2,4,6-trifluorophenyl) complex-es (P–P)Ni(2,4,6-C 6 H 2 F 3 ) 2 containing either MeOBiPhep (3a) or macrocyclic bisphosphine ligand (3b-3e) as a func-tion of force applied to the biaryl backbone of these ligands through intramolecular tension generated by a molecular force probe. Nickel complexes 3 were isolated in 22-60% yield from reaction of bisphosphine with the bis(tetrahydrofuranyl) complex (THF) 2 Ni(2,4,6-C 6 H 2 F 3 ) 2 followed by chromatography. Thermolysis of complexes 3 in C 6 D 6 at 68 °C leads to first-order decay through > 3 half-lives to form 2,2',4,4',6,6'-hexaflurorobiphenyl as the exclusive fluorine-containing product in ≥93% yield. Whereas compressive forces up to –65 pN have no significant effect on the rate of reductive elimination, extension forces increase the rate of reductive elimination by a factor of three over a ~230 pN range of restoring forces relative to the strain-free MeOBiphep complex. Furthermore, the rate response of reductive elimination from nickel(II) bis(trifluorophenyl) complexes as a function of extension force is similar to the previously reported 2.8-fold increase in the rate of reductive elimination from platinum diaryl complexes (P–P)Pt(4-C 6 H 4 NMe 2 ) 2 over the same range of forces

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Chloride, Alkoxide, or Silicon: The Bridging Ligand Dictates the Spin State in Dicobalt Expanded Pincer Complexes

We report the synthesis and characterization of a series of high- and low-spin dicobalt complexes of the tBu PNNP expanded pincer ligand. Reacting this dinucleating ligand in its neutral form with two equiv of CoCl 2 (tetrahydrofuran) 1.5 yields a high-spin dicobalt complex featuring one Co inside and one Co outside of the dinucleating pocket. Performing the same reaction in the presence of two equivalents of KOtBu provides access to a high-spin dicobalt complex wherein both Co centers are bound within the PNNP pocket, and this complex also features a bridging OtBu ligand. Reacting either of the high-spin complexes with excess diethyl silane affords a low-spin dicobalt complex containing two unusual bridging Si-based ligands. These complexes were investigated using NMR spectroscopy, XAS, single crystal X-ray structure determination, and computational methods, showing that the Si-based ligands are best described as base-stabilized silylenes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Assessment of Quantum Mechanical Methods for Copper and Iron Complexes by Photoelectron Spectroscopy

Broken-symmetry density functional theory (BS-DFT) calculations are assessed for redox energetics [Cu(SCH3)2]1–/0, [Cu(NCS)2]1–/0, [FeCl4]1–/0, and [Fe(SCH3)4]1–/0 against vertical detachment energies (VDE) from valence photoelectron spectroscopy (PES), as a prelude to studies of metalloprotein analogs. The M06 and B3LYP hybrid functionals give VDE that agree with the PES VDE for the Fe complexes, but both underestimate it by 400 meV for the Cu complexes; other hybrid functionals give VDEs that are an increasing function of the amount of Hartree–Fock (HF) exchange and so cannot show good agreement for both Cu and Fe complexes. Range-separated (RS) functionals appear to give a better distribution of HF exchange since the negative HOMO energy is approximately equal to the VDEs but also give VDEs dependent on the amount of HF exchange, sometimes leading to ground states with incorrect electron configurations; the LRC-ωPBEh functional reduced to 10% HF exchange at short-range give somewhat better values for both, although still 150 meV too low for the Cu complexes and 50 meV too high for the Fe complexes. Overall, the results indicate that while HF exchange compensates for self-interaction error in DFT calculations of both Cu and Fe complexes, too much may lead to more sensitivity to nondynamical correlation in the spin-polarized Fe complexes.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Understanding the Electronic Structure of 4d Metal Complexes: From Molecular Spinors to L-Edge Spectra of a di-Ru Catalyst

L{sub 2,3}-edge X-ray absorption spectroscopy (XAS) has demonstrated unique capabilities for the analysis of the electronic structure of di-Ru complexes such as the blue dimer cis,cis-[Ru{sub 2}{sup III}O(H{sub 2}O){sub 2}(bpy){sub 4}]{sup 4+} water oxidation catalyst. Spectra of the blue dimer and the monomeric [Ru(NH{sub 3}){sub 6}]{sup 3+} model complex show considerably different splitting of the Ru L{sub 2,3} absorption edge, which reflects changes in the relative energies of the Ru 4d orbitals caused by hybridization with a bridging ligand and spin-orbit coupling effects. To aid the interpretation of spectroscopic data, we developed a new approach, which computes L{sub 2,3}-edges XAS spectra as dipole transitions between molecular spinors of 4d transition metal complexes. This allows for careful inclusion of the spin-orbit coupling effects and the hybridization of the Ru 4d and ligand orbitals. The obtained theoretical Ru L{sub 2,3}-edge spectra are in close agreement with experiment. Critically, existing single-electron methods (FEFF, FDMNES) broadly used to simulate XAS could not reproduce the experimental Ru L-edge spectra for the [Ru(NH{sub 3}){sub 6}]{sup 3+} model complex nor for the blue dimer, while charge transfer multiplet (CTM) calculations were not applicable due to the complexity and low symmetry of the blue dimer water oxidation catalyst. We demonstrated that L-edge spectroscopy is informative for analysis of bridging metal complexes. The developed computational approach enhances L-edge spectroscopy as a tool for analysis of the electronic structures of complexes, materials, catalysts, and reactive intermediates with 4d transition metals.

Alperovich, Igor↗
DOE OSTI2021

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

We report two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) 3 (2) with KC 8 yields the anionic bis(arene) complex [K[2.2.2]cryptand][U(TDA) 2 ] (3) (TDA = N-(2,6-di-isopropylphenyl)pivalamido). EPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f 4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a two-electron reductant toward I 2 to form the dinuclear U(III)–U(III) triiodide species [K[2.2.2]cryptand][(UI(TDA) 2 ) 2 (μ-I)] (6) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex [K[2.2.2]cryptand][U(η 7 -C 7 H 7 )(TDA) 2 (THF)] (7). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion [K[2.2.2]cryptand][U(TDA) 4 ] (1-crypt) and U(COT) 2 , while the addition of COT to complex 2 instead yields the dinuclear U(IV)–U(IV) inverse sandwich complex [U(TDA) 3 ] 2 (μ-η 8 :η 3 -C 8 H 8 ) (8). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA) 4 (4) with KC 8 gives the mono(arene) complex [K[2.2.2]cryptand][Th(TDA) 3 (THF)] (5). The C–C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Rapid Electron Transfer Self-Exchange in Conformationally Dynamic Copper Coordination Complexes

Here we report the electron transfer (ET) self-exchange rate constants (k 11 ) for a pair of Cu II/I complexes utilizing dpa R (dpa = dipicolylaniline, R = OMe, SMe) ligands assessed by NMR line-broadening experiments. These ligands afford copper complexes that are conformationally dynamic in one oxidation state. With R = OMe, the Cu I complex is dynamic, while with R= SMe, the Cu II complex is dynamic. Both complexes exhibit unexpectedly large k 11 of 2.48(6) x 10 5 and 2.21(9) × 10 6 M –1 s –1 for [CuCl(dpa OMe )] +/0 and [CuCl(dpa SMe )] +/0 , respectively. Among the fastest reported for molecular copper coordination complexes to date, that of [CuCl(dpa SMe )] +/0 exceeds all others by an order of magnitude and compares only to those observed in type 1 blue copper proteins. The dynamicity of these complexes establish pre-steady-state con-formational equilibria that minimize the inner sphere reorganization energies to 0.71 and 0.62 eV for R = OMe and SMe, respectively. In contrast to the emphasis on rigidity in the formulation of entatic states applied to blue copper proteins, the success of these two systems highlight the relevance of conformational dynamicity in mediating rapid ET.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

pH-Dependent Vibrational Dynamics Drives Excited-State Quenching in the Phycobiliprotein Complex PC645

Phycocyanin 645 (PC645) is a closed-form lightharvesting complex found in the lumen of the photosynthetic membrane of cryptophyte algae. These peripheral antenna complexes contain bilin chromophores that absorb sunlight and transfer excitation energy to the core antenna complexes embedded in the thylakoid membrane. The location of cryptophyte antenna complex on the luminal side of the membrane is unusual. During photosynthetic activity, the pH of the lumen drops, by up to two pH units. There is little known about how this pH-change affects the light-harvesting complexes. In this study, we report multiscale simulations using a computationally efficient density functional tight-binding framework to investigate the spectroscopy and excitation energy transfer in the PC645 complex. Complementary experiments were conducted using both steady-state and time-resolved spectroscopic measurements at low, neutral, and high pH values. Our study shows that (de)protonation of specific bilin pigments, namely, the mesobiliverdins (MBVs), modulates the excitation energies, excitonic couplings, and spectral densities. These changes cause excitation transfer rates to increase by up to a factor of two to three, leading to pH-dependent energy transfer pathways in the complex. Using this model, we calculated the pH-dependent fluorescence quantum yield of the system, obtaining quantitative agreement with the experimental results. These computational simulations, supported by experiments, identify MBVs as a more prominent excitation sink than previously realized, and that this role is tuned by pH.

Maity, Sayan [Constructor Univ., Bremen (Germany);↗
DOE OSTI2017

End-On Bridging Dinitrogen Complex of Scandium

The first (N=N) 2- complex of a rare-earth metal with an end-on dinitrogen bridge, {K(crypt)} 2 {[(R 2 N) 3 Sc] 2 [μ-η 1 :η 1 -n 2 ]} (crypt = 2.2.2-cryptand, R = SiMe 3 ), has been isolated from the reduction of Sc(NR 2 ) 3 under dinitrogen at —35 °C and characterized by X-ray crystallography. The structure differs from the characteristic side-on structures previously observed for over 40 crystallographically-characterized rare-earth metal (N=N) 2- complexes of formula [A 2 Ln(THF) x ] 2 [μ-η 2 :η 2 -N 2 ] (Ln = Sc, Y, and lanthanides; x = 0, 1; A = anionic ligand such as amide, cyclopentadienide, and aryloxide). The 1.221(3) Å N—N distance and the 1644 cm -1 Raman stretch are consistent with the presence of an (N=N) 2- bridge. The observed paramagnetism of the complex by NMR spectroscopy and Evans method measurements is consistent with DFT calculations that suggest a triplet( 3 A 2 ) ground state in D 3 symmetry involving two degenerate Sc—N 2 —Sc bonding orbitals. Upon brief exposure of the orange Sc 3+ bridging dinitrogen complex to UV-light, photolysis to form the monomeric Sc 2+ complex, [K(crypt)][Sc(NR 2 ) 3 ], was observed. Conversion of the Sc 2+ complex to the SO 3+ dinitrogen complex was not observed with this crypt system, but it did occur with the 18-crown-6 (crown) analog which formed {K(crown)} 2 {[(R 2 N) 3 Sc] 2 [μ-η 1 :η 1 -N 2 ]}. This suggests the importance of the alkali metal chelating agent in the reversibility of dinitrogen binding in this scandium system.

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

In-Plane Thorium(IV), Uranium(IV), and Neptunium(IV) Expanded Porphyrin Complexes

In our research, we report a first series of in-plane thorium(IV), uranium(IV), and neptunium(IV) expanded porphyrin complexes. These actinide (An) complexes were synthesized using a hexa-aza porphyrin analogue, termed dipyriamethyrin, and the non-aqueous An(IV) precur-sors: ThCl 4 (DME) 2 , UCl 4 , and NpCl 4 (DME) 2 under conditions of in situ sodium bis(trimethylsilyl)amide deprotonation. The molecu-lar and electronic structure of the ligand, each An(IV) complex, and a corresponding uranyl(VI) complex were characterized using NMR and UV-vis spectroscopies, as well as single crystal X-ray diffraction analysis. Computational analyses of these complexes, coupled with their structural features, provide support for the conclusion that a greater degree of covalency in the ligand-cation orbital interactions arises as the early actinide series is traversed from Th(IV) to U(IV) and Np(IV). The axial ligands in the current An(IV) complexes proved labile, allowing for the electronic features of these complexes to be further modified.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Second Coordination Sphere Effects in an Evolved Ru Complex Based on Highly Adaptable Ligand Results in Rapid Water Oxidation Catalysis

A new Ru complex containing the deprotonated 2,2':6',2"-terpyridine-6,6"-diphosphonic acid (H 4 tPa) and pyridine (py) of general formula [Ru II (H 3 tPa-κ-N 3 O)(py) 2 ] + , 2 + , has been prepared and thoroughly characterized by means of spectroscopic and electrochemical techniques, X-ray diffraction analysis, and density functional theory (DFT) calculations. Complex 2 + presents a dynamic behavior in the solution that involves the synchronous coordination and the decoordination of the dangling phosphonic groups of the tPa 4– ligand. Yet, at oxidation state IV, complex 2 + becomes seven coordinated with the two phosphonic groups now bonded to the metal center. Further, at this oxidation state at neutral and basic pH, the Ru complex undergoes the coordination of an exogenous OH – group from the solvent that leads to an intramolecular aromatic O atom insertion into the CH bond of one of the pyridyl groups, forming the corresponding phenoxo-phosphonate Ru complex [Ru III (tPaO-κ-N 2 O P O C )(py) 2 ] 2– , 4 2– , where tPaO 5– is the 3-(hydroxo-[2,2':6',2"-terpyridine]-6,6"-diyl)bis(phosphonate) ligand. This new in situ generated Ru complex, 4 2– , has been isolated and spectroscopically and electrochemically characterized. In addition, a crystal structure has been also obtained using single-crystal X-ray diffraction techniques. Complex 4 2– turns out to be an exceptional water oxidation catalyst achieving record maximum turnover frequencies (TOF max ) on the order of 16 000 s –1 . A mechanistic analysis complemented with DFT calculations has further been carried out, showing the critical role of intramolecular second coordination sphere effects exerted by the phosphonate groups in lowering the activation energy at the rate-determining step.

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

Single-photon test of hyper-complex quantum theories using a metamaterial

In standard quantum mechanics, complex numbers are used to describe the wavefunction. Although this has so far proven sufficient to predict experimental results, there is no theoretical reason to choose them over real numbers or generalizations of complex numbers, that is, hyper-complex numbers. Experiments performed to date have proven that real numbers are insufficient, but the need for hyper-complex numbers remains an open question. Here we experimentally probe hyper-complex quantum theories, studying one of their deviations from complex quantum theory: the non-commutativity of phases. We do so by passing single photons through a Sagnac interferometer containing both a metamaterial with a negative refractive index, and a positive phase shifter. In order to accomplish this we engineered a fishnet metamaterial to have a negative refractive index at 780 nm. Here, we show that the metamaterial phase commutes with other phases with high precision, allowing us to place limits on a particular prediction of hyper-complex quantum theories.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Yeast Nup84-Nup133 complex structure details flexibility and reveals conservation of the membrane anchoring ALPS motif

The hallmark of the eukaryotic cell is the complex endomembrane system that compartmentalizes cellular functions. Transport into and out of the nucleus occurs through the nuclear pore complex (NPC). The heptameric Nup84 or Y complex is an essential scaffolding component of the NPC. Here we report two nanobody-bound structures: the full-length Nup84-Nup133 C-terminal domain complex and the Nup133 N-terminal domain, both from S. cerevisiae. Together with previously published structures, this work enables the structural description of the entire 575 kDa Y complex from one species. The structure of Nup84-Nup133CTD details the high flexibility of this dimeric unit of the Y complex. Further, the Nup133NTD contains a structurally conserved amphipathic lipid packing sensor motif, confirmed by liposome interaction studies. The presented structures reveal important details about the function of the Y complex that affect our understanding of NPC structure and assembly.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes

Oxygen, one of the most abundant elements on Earth, often forms an undesired interstitial impurity or ceramic phase (such as an oxide particle) in metallic materials. Even when it adds strength, oxygen doping renders metals brittle. Here, in this study, we show that oxygen can take the form of ordered oxygen complexes, a state in between oxide particles and frequently occurring random interstitials. Unlike traditional interstitial strengthening, such ordered interstitial complexes lead to unprecedented enhancement in both strength and ductility in compositionally complex solid solutions, the so-called high-entropy alloys (HEAs). The tensile strength is enhanced (by 48.5 ± 1.8 per cent) and ductility is substantially improved (by 95.2 ± 8.1 per cent) when doping a model TiZrHfNb HEA with 2.0 atomic per cent oxygen, thus breaking the long-standing strength–ductility trade-off. The oxygen complexes are ordered nanoscale regions within the HEA characterized by (O, Zr, Ti)-rich atomic complexes whose formation is promoted by the existence of chemical short-range ordering among some of the substitutional matrix elements in the HEAs. Carbon has been reported to improve strength and ductility simultaneously in face-centred cubic HEAs, by lowering the stacking fault energy and increasing the lattice friction stress. By contrast, the ordered interstitial complexes described here change the dislocation shear mode from planar slip to wavy slip, and promote double cross-slip and thus dislocation multiplication through the formation of Frank–Read sources (a mechanism explaining the generation of multiple dislocations) during deformation. This ordered interstitial complex-mediated strain-hardening mechanism should be particularly useful in Ti-, Zr- and Hf-containing alloys, in which interstitial elements are highly undesirable owing to their embrittlement effects, and in alloys where tuning the stacking fault energy and exploiting athermal transformations do not lead to property enhancement. These results provide insight into the role of interstitial solid solutions and associated ordering strengthening mechanisms in metallic materials.

Lei, Zhifeng↗