Bruce E. Bursten

Bio: Bruce E. Bursten is an academic researcher from University of Tennessee. The author has contributed to research in topics: Molecular orbital & Electronic structure. The author has an hindex of 42, co-authored 178 publications receiving 5721 citations. Previous affiliations of Bruce E. Bursten include University of Virginia & Los Alamos National Laboratory.

Structure and Bonding in SnWO4, PbWO4, and BiVO4: Lone Pairs vs Inert Pairs

Abstract: Three ternary oxides, SnWO4, PbWO4, and BiVO4, containing p-block cations with ns2np0 electron configurations, so-called lone pair cations, have been studied theoretically using density functional theory and UV−visible diffuse reflectance spectroscopy The computations reveal significant differences in the underlying electronic structures that are responsible for the varied crystal chemistry of the lone pair cations The filled 5s orbitals of the Sn2+ ion interact strongly with the 2p orbitals of oxygen, which leads to a significant destabilization of symmetric structures (scheelite and zircon) favored by electrostatic forces The destabilizing effect of this interaction can be significantly reduced by lowering the symmetry of the Sn2+ site to enable the antibonding Sn 5s−O 2p states to mix with the unfilled Sn 5p orbitals This interaction produces a localized, nonbonding state at the top of the valence band that corresponds closely with the classical notion of a stereoactive electron lone pair In compo

Noble gas-actinide compounds: complexation of the CUO molecule by Ar, Kr, and Xe atoms in noble gas matrices.

Abstract: The CUO molecule, formed from the reaction of laser-ablated U atoms with CO in a noble gas, exhibits very different stretching frequencies in a solid argon matrix [804.3 and 852.5 wave numbers (cm−1)] than in a solid neon matrix (872.2 and 1047.3 cm−1). Related experiments in a matrix consisting of 1% argon in neon suggest that the argon atoms are interacting directly with the CUO molecule. Relativistic density functional calculations predict that CUO can bind directly to one argon atom (U-Ar = 3.16 angstroms; binding energy = 3.2 kilocalories per mole), accompanied by a change in the ground state from a singlet to a triplet. Our experimental and theoretical results also suggest that multiple argon atoms can bind to a single CUO molecule.

Neptunium redox speciation

Abstract: Insights about the redox speciation of neptunium in an aqueous mineral acid electrolyte were obtained through a combination of in situ EXAFS (extended X-ray absorption fine structure) spectroelectrochemistry, density functional theory (DFT), and simple geometric modeling. A single solution of neptunium in 1 M perchloric acid was used to extract metrical information about the Np coordination environment, in terms of hydration numbers (n) and Np-O interatomic distances. Four aquo ions - Np3+·nH2O, Np4+ · n´H2O, [Np5+O2]+ · n´´H2O, and [Np6+O2]2+ · n´´´H2O - were electrolytically prepared and precisely maintained by use of constant potential bulk electrolysis (with coulometry) throughout the simultaneous EXAFS data acquisition. For the Np(III) and Np(IV) aquo ions, the experiments revealed a contraction of the average Np-O bond lengths from 2.48(2) to 2.37(2) Å, respectively. The data analyses suggest that there are 9 water molecules in the first or inner hydration sphere about Np3+ in [Np(OH2)9]3+ and Np4+ in [Np(OH2)9]4+. The DFT calculations reveal 8-9 water molecules coordinated to Np(III), supporting the EXAFS results. Simple geometric modeling supports a coordination number of 8 for both trivalent and tetravalent Np. For the Np(V) and Np(VI) aquo ions, the EXAFS revealed bond length contractions. The average interatomic distances for the trans-dioxygen atoms in [NpO2]+ and [NpO2]2+ decreased from 1.80(2) Å for Np(V) to 1.73(2) Å for Np(VI). The average interatomic distances to the oxygen atoms of the coordinated H2O molecules decreased from 2.44(3) Å to 2.36(3) Å, respectively. The oxygen coordination numbers were identical, suggesting that 5 water molecules are bound to Np5+ in [NpO2(OH2)5]+ and to Np6+ in [NpO2(OH2)5]2+.

Molecular single-bond covalent radii for elements 1-118.

Abstract: A self-consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1-18, Z=1-118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E-E, E-H, and E-CH 3 data are incorporated for most elements, E. Many E-E' data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl-based one of Suresh and Koga [J. Phys. Chem. A 2001, 105, 5940] and its predecessors. For the diatomic alkalis MM' and halides XX', separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition-metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H 2 and F 2 . The standard deviation for the 410 included data points is 2.8 pm.

Catalysts for Suzuki−Miyaura Coupling Processes: Scope and Studies of the Effect of Ligand Structure

Abstract: Suzuki−Miyaura coupling reactions of aryl and heteroaryl halides with aryl-, heteroaryl- and vinylboronic acids proceed in very good to excellent yield with the use of 2-(2‘,6‘-dimethoxybiphenyl)dicyclohexylphosphine, SPhos (1). This ligand confers unprecedented activity for these processes, allowing reactions to be performed at low catalyst levels, to prepare extremely hindered biaryls and to be carried out, in general, for reactions of aryl chlorides at room temperature. Additionally, structural studies of various 1·Pd complexes are presented along with computational data that help elucidate the efficacy that 1 imparts on Suzuki−Miyaura coupling processes. Moreover, a comparison of the reactions with 1 and with 2-(2‘,4‘,6‘-triisopropylbiphenyl)diphenylphosphine (2) is presented that is informative in determining the relative importance of ligand bulk and electron-donating ability in the high activity of catalysts derived from ligands of this type. Further, when the aryl bromide becomes too hindered, an ...

Rationally Designing High-Performance Bulk Thermoelectric Materials

Abstract: There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of th...

Density functional theory for transition metals and transition metal chemistry

Abstract: We introduce density functional theory and review recent progress in its application to transition metal chemistry. Topics covered include local, meta, hybrid, hybrid meta, and range-separated functionals, band theory, software, validation tests, and applications to spin states, magnetic exchange coupling, spectra, structure, reactivity, and catalysis, including molecules, clusters, nanoparticles, surfaces, and solids.

Jaguar: A high-performance quantum chemistry software program with strengths in life and materials sciences

Abstract: Jaguar is an ab initio quantum chemical program that specializes in fast electronic structure predictions for molecular systems of medium and large size. Jaguar focuses on computational methods with reasonable computational scaling with the size of the system, such as density functional theory (DFT) and local second-order Moller–Plesset perturbation theory. The favorable scaling of the methods and the high efficiency of the program make it possible to conduct routine computations involving several thousand molecular orbitals. This performance is achieved through a utilization of the pseudospectral approximation and several levels of parallelization. The speed advantages are beneficial for applying Jaguar in biomolecular computational modeling. Additionally, owing to its superior wave function guess for transition-metal-containing systems, Jaguar finds applications in inorganic and bioinorganic chemistry. The emphasis on larger systems and transition metal elements paves the way toward developing Jaguar for its use in materials science modeling. The article describes the historical and new features of Jaguar, such as improved parallelization of many modules, innovations in ab initio pKa prediction, and new semiempirical corrections for nondynamic correlation errors in DFT. Jaguar applications in drug discovery, materials science, force field parameterization, and other areas of computational research are reviewed. Timing benchmarks and other results obtained from the most recent Jaguar code are provided. The article concludes with a discussion of challenges and directions for future development of the program. © 2013 Wiley Periodicals, Inc.