Aromaticity and antiaromaticity, as defined by Hückel’s rule, are key ideas in organic chemistry, and are both exemplified in biphenylene—a molecule that consists of two benzene rings joined by a four-membered ring at its core. Biphenylene analogues in which one of the benzene rings has been replaced by a different (4n + 2) π-electron system have so far been associated only with organic compounds. In addition, efforts to prepare a zirconabiphenylene compound resulted in the isolation of a bis(alkyne) zirconocene complex instead. Here we report the synthesis and characterization of, to our knowledge, the first 2-metallabiphenylene compounds. Single-crystal X-ray diffraction studies reveal that these complexes have nearly planar, 11-membered metallatricycles with metrical parameters that compare well with those reported for biphenylene. Nuclear magnetic resonance spectroscopy, in addition to nucleus-independent chemical shift calculations, provides evidence that these complexes contain an antiaromatic cyclobutadiene ring and an aromatic benzene ring. Finally, spectroscopic evidence, Kohn–Sham molecular orbital compositions and natural bond orbital calculations suggest covalency and delocalization of the uranium f 2 electrons with the carbon-containing ligand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Development of Density Functional Tight-Binding Parameters Using Relative Energy Fitting and Particle Swarm Optimization

We provide a strategy to optimize density functional tight-binding (DFTB) parameterization for the calculation of the structures and properties of organic molecules consisting of hydrogen, carbon, nitrogen, and oxygen. We utilize an objective function based on similarity measurements and the Particle Swarm Optimization (PSO) method to find an optimal set of parameters. This objective function considers not only the common DFTB descriptors of binding energies and atomic forces but also incorporates relative energies of isomers into the fitting procedure for more chemistry-driven results. The quality in the description of the binding energies and atomic forces is measured based on the Ballester similarity index and relative energies through a similarity index induced by the Levenshtein edit distance to quantify the correct energetic order of isomers. Training and testing datasets were created to include all relevant chemical functional groups. Finally, the accuracy of this strategy is assessed, and its range of applicability is discussed by comparison against our previous parameterization. The improved performance of the new DFTB parameterization is validated with respect to the density functional theory large datasets QM-9 and ANI-1, where excellent agreement is found between the structures and properties available in these datasets, and the ones obtained with DFTB.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

“Sweeping” Ortho Substituents Drive Desolvation and Overwhelm Electronic Effects in Nd 3+ Chelation: A Case of Three Aryldithiophosphinates

Bis[o-(trifluoromethyl)phenyl]dithiophosphinate is a sulfur-donating ligand capable of providing the largest reported trivalent lanthanide (Ln 3+ )–actinide (An 3+ ) group separation factors. Literature has reflected that the placement and number of the-CF3 functionalities on the aryl rings proximate to the ligating sulfur atoms can significantly impact Ln 3+ –An 3+ extraction and separation factors, but the complexation thermodynamics of -CF 3 -derivatized aryldithiophosphinates have not been considered to date. This systematic report considers the complexation of three CF 3 -substituted aryldithiophosphinates—bis(phenyl)dithiophosphinate (L I ), [o-(trifluoromethyl)phenyl](phenyl)dithiophosphinate (L II ), and bis[o-(trifluoromethyl)phenyl]dithiophosphinate (L III ), with Nd 3+ in an ethanolic environment. The chelating ability of NdIII by these ligands follows the order of L III > L II > L I , which is in line with the reported extraction efficiency. The positive ΔS, as well as positive ΔH, suggests that Nd 3+ chelation is entropy-driven and effective desolvation is critical to enabling Nd 3+ interaction with otherwise weakly interacting sulfur-containing ligands. Extended X-ray absorption fine structure results confirm thermodynamic investigations and suggest that L I can only form up to 1:2 (M–L) complexes, while L II and L III form up to 1:3 complexes with Nd 3+ . All three L III anions have bidentate interactions with Nd III , but two L II anions have bidentate interactions with Nd 3+ , while the third LII anion is monodentate. The significant increase in ΔS with each o-CF 3 addition suggests aiding desolvation could be central in enabling f-element interaction with weakly interacting donor groups, and this report provides a method to controlling f-element desolvation as an innovative f-element chelating strategy.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2019

Thickness-dependent polarization-induced intrinsic magnetoelectric effects in L a 0.67 S r 0.33 Mn O 3 / PbZ r 0.52 T i 0.48 O 3 heterostructures

The polarization of PbZr 0.52 Ti 0.48 O 3 thin film is switched by changing film thickness through the competition between the strain relaxation-induced flexoelectric fields and the interfacial effects. Without an applied electric field, this reversal of polarization is exploited to control the magnetic properties of La 0.67 Sr 0.33 MnO 3 by the competition/cooperation between the charge-mediated and the strain-mediated effects. Scanning transmission electron microscopy, polarized near-edge x-ray absorption spectroscopy, and half-integer diffraction measurements are employed to decode the intrinsic magnetoelectric effects in the La 0.67 Sr 0.33 MnO 3 /PbZr 0.52 Ti 0.48 O 3 heterostructures. Here, with PbZr 0.52 Ti 0.48 O 3 films <48nm, the polarization-driven carrier density modulation around the La 0.67 Sr 0.33 MnO 3 /PbZr 0.52 Ti 0.48 O 3 interface and the strain-mediated Mn 3d orbital occupancy work together to enhance the magnetism of 14-unit-cell La 0.67 Sr 0.33 MnO 3 film; with PbZr 0.52 Ti 0.48 O 3 layers > 48nm, the strain-induced change of bond length/angle of MnO 6 accompanied with a modified spin configuration are responsible for the decrease in the Curie temperature and magnetization of 14-unit-cell La 0.67 Sr 0.33 MnO 3 film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Halide anion discrimination by a tripodal hydroxylamine ligand in gas and condensed phases

Electrospray ionization of solutions containing a tripodal hydroxylamine ligand, H 3 TriNOx ([((2- t BuNOH)C 6 H 4 CH 2 ) 3 N]) denoted as L, and a hydrogen halide HX: HCl, HBr and/or HI, yielded gas-phase anion complexes [L(X)] - and [L(HX2)] - . Collision induced dissociation (CID) of mixed-halide complexes, [L(HX a X b )] - , indicated highest affinity for I - and lowest for Cl - . Structures and energetics computed by density functional theory are in accord with the CID results, and indicate that the gas-phase binding preference is a manifestation of differing stabilities of the HX molecules. A high halide affinity of [L(H)] + in solution was also demonstrated, though with a highest preference for Cl - and lowest for I - , the opposite observation of, but not in conflict with, what is observed in gas phase. Finally, the results suggest a connection between gas- and condensed-phase chemistry and computational approaches, and shed light on the aggregation and anion recognition properties of hydroxylamine receptors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Design, Isolation, and Spectroscopic Analysis of a Tetravalent Terbium Complex

Synthetic strategies to glean molecular complexes of high-valent lanthanides, other than the ubiquitous Ce 4+ ion, are exceptionally rare, and thorough, detailed characterization in these systems is limited by complex lifetime and reaction and isolation conditions. The synthesis of high-symmetry complexes in high purity with significant lifetimes in solution and the solid state is essential for determining the role of ligand-field splitting, multiconfigurational behavior, and covalency in governing the reactivity and physical properties of these potentially technologically transformative tetravalent ions. We report the synthesis and physical characterization of an S 4 symmetric, four-coordinate tetravalent terbium complex, [Tb(NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (where Et is ethyl and t Bu is tert-butyl). The ligand field in this complex is weak and the metal–ligand bonds sufficiently covalent so that the tetravalent terbium ion is stable and accessible via a mild oxidant from the anionic, trivalent, terbium precursor, [(Et 2 O)K][Tb(NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ]. The crucial stability of the tetravalent complex enables its thorough characterization. The stepwise development of the supporting ligand points to key ligand control elements for further extending the known tetravalent lanthanide ions in molecular complexes. Magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray absorption near-edge spectroscopy (XANES), and density functional theory studies indicate a 4ƒ 7 ground state for [Tb(NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] with considerable zero-field splitting, demonstrating that magnetic, tetravalent lanthanide ions engage in covalent metal–ligand bonds. This result has significant implications for the use of tetravalent lanthanide ions in magnetic applications since the observed zero-field splitting is intermediate between that observed for the trivalent lanthanides and for the transition metals. The similarity of the multiconfigurational behavior in the ground state of [Tb(NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (measured by Tb L 3 -edge XAS) to that observed in TbO 2 implicates ligand control of multiconfigurational behavior as a key component of the stability of the complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

[Am(C 5 Me 4 H) 3 ]: An Organometallic Americium Complex

Abstract We report the small‐scale synthesis, isolated yield, single‐crystal X‐ray structure, 1 H NMR solution spectroscopy /solid‐state UV/Vis‐nIR spectroscopy, and density functional theory (DFT)/ab initio wave function theory calculations on an Am 3+ organometallic complex, [Am(C 5 Me 4 H) 3 ] ( 1 ). This constitutes the first quantitative data on Am−C bonding in a molecular species.

Goodwin, Conrad A. P.↗

DOE OSTI2019

[Am(C 5 Me 4 H) 3 ], an organometallic americium complex

Organometallic synthetic chemistry of transplutonium elements is an area that has been stagnant for decades. Here, we observe the small-scale synthesis, isolated yield, single-crystal X-ray structure, 1H NMR, solution/solid-state UV-vis-nIR spectroscopy, and Density Functional Theory/ab initio Wave Functional Theory calculations on an Am3+ organometallic complex,[Am(C 5 Me 4 H) 3 ]. This constitutes the first quantitative data on Am–C bonding in a molecular species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Solubility model of metal complex in ionic liquids from first principle calculations

A predictive model based on first principles calculations has been proposed to study the solid–liquid equilibria comprising of metal complexes and ionic liquids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Interdisciplinary round-robin test on molecular spectroscopy of the U(VI) acetate system

In the advent of the 2nd International Workshop on Advanced Techniques in Actinide Spec-troscopy (ATAS 2014), an inter-laboratory round-robin test (RRT) was initiated. The main goal of this RRT was the comprehensive molecular analysis of a simple aqueous complexing system – U(VI) acetate – which was selected to be independently investigated by various 100 spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods applied by leading laboratories in actinide or geochemical research. Ultimately, more than 40 scientists hosted at 20 institutions in 7 coun-tries participated. The outcome of this RRT were considered on two levels: First, conformities as well as 105 discrepancies in the results of each spectroscopic technique and their sources were evaluated. The raw data from the experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was surprisingly high. By contrast, the data obtained using luminescence spectroscopy turned out to be strongly related to the chosen acquisition param-110 eters. Second, the potentials and limitations of coupling various spectroscopic and, in partic-ular, theoretical approaches for the comprehensive study of actinide molecule complexes were assessed. The additional benefits of the combined approach with regard to the explora-tion of the aqueous speciation of the U(VI) acetate system were elaborated.

Muller, Katharina↗

DOE OSTI2019

Enthalpies of formation and phase stability relations of USi, U 3 Si 5 and U 3 Si 2

U–Si intermetallic compounds have drawn great attention due to their potential application as nuclear fuels. However, the thermodynamic properties and phase equilibria of this binary system from ambient to high temperature conditions are not fully understood. Via high temperature oxidative drop calorimetry and detailed characterization of the initial and final phases, we have experimentally determined the standard enthalpies of formation of USi and U 3 Si 5.07 at 298 K to be –43.2 ± 6.2 and –43.8 ± 9.0 kJ/mol·atom, respectively. The energetics of the tetragonal USi (t-USi, space group I 4/ mmm ) phase has also been calculated with Density Functional Theory (DFT) for the first time. Combining the obtained formation enthalpies with the heat capacities measured previously, we assessed the thermodynamic stability of t-USi relative to a phase assemblage of two other U–Si phases, U 3 Si 5.07 and U 3 Si 2 , from ambient temperature to 1200 K. The tetragonal USi is thermodynamically more stable than U 3 Si 5.07 + U 3 Si 2 , which supports previously published phase diagram (H. Okamoto and T. Massalski, 1990 [1]): specifically, at least one stable USi phase exists when the U content is 50 at.%. In conclusion, further thermodynamic and phase equilibrium studies are needed for a more comprehensive understanding of the U–Si system across broader compositional and temperature ranges.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2019

Large spin-orbit torque efficiency enhanced by magnetic structure of collinear antiferromagnet IrMn

Spin-orbit torque (SOT) offers promising approaches to developing energy-efficient memory devices by electric switching of magnetization. Compared to other SOT materials, metallic antiferromagnet (AFM) potentially allows the control of SOT through its magnetic structure. Here, combining the results from neutron diffraction and spin-torque ferromagnetic resonance experiments, we show that the magnetic structure of epitaxially grown L1 0 -IrMn (a collinear AFM) is distinct from the widely presumed bulk one. It consists of twin domains, with the spin axes orienting toward [111] and [–111], respectively. This unconventional magnetic structure is responsible for much larger SOT efficiencies up to 0.60 ± 0.04, compared to 0.083 ± 0.002 for the polycrystalline IrMn. Furthermore, we reveal that this magnetic structure induces a large isotropic bulk contribution and a comparable anisotropic interfacial contribution to the SOT efficiency. Our findings shed light on the critical roles of bulk and interfacial antiferromagnetism to SOT generated by metallic AFM.

36 MATERIALS SCIENCE↗