Arthur J. Schultz
Argonne National Laboratory
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Science | 1991
Jack M. Williams; Arthur J. Schultz; Urs Geiser; K. Douglas Carlson; Aravinda M. Kini; H. Hau Wang; Wai Kwong Kwok; Myung-Hwan Whangbo; J. E. Schirber
Recent advances in the design and synthesis of organic synthetic metals have yielded materials that have the highest superconducting transition temperatures (Tc ≈ 13 kelvin) reported for these systems. These materials have crystal structures consisting of alternating layers of organic donor molecules and inorganic anions. Organic superconductors have various electronic and magnetic properties and crystal structures that are similar to those of the inorganic copper oxide superconductors (which have high Tc values); these similarities include highly anisotropic conductivities, critical fields, and short coherence lengths. The largest number of organic superconductors, including those with the highest Tc values, are charge-transfer salts derived from the electron donor molecule BEDT-TTF or ET [bis(ethylenedithio)-tetrathiafulvalene]. The synthesis and crystal structures of these salts are discussed; their electrical, magnetic, and band electronic structure properties and their many similarities to the copper oxide superconductors are treated as well.
Journal of the American Chemical Society | 2008
Travis J. Hebden; Melanie C. Denney; Vincent Pons; Paula M. B. Piccoli; Thomas F. Koetzle; Arthur J. Schultz; Werner Kaminsky; Karen I. Goldberg; D. Michael Heinekey
Reaction of NaBH4 with (tBuPOCOP)IrHCl affords the previously reported complex (tBuPOCOP)IrH2(BH3) (1) (tBuPOCOP = kappa(3)-C6H3-1,3-[OP(tBu)2]2). The structure of 1 determined from neutron diffraction data contains a B-H sigma-bond to iridium with an elongated B-H bond distance of 1.45(5) A. Compound 1 crystallizes in the space group P1 (Z = 2) with a = 8.262 (5) A, b = 12.264 (5) A, c = 13.394 (4) A, and V = 1256.2 (1) A(3) (30 K). Complex 1 can also be prepared by reaction of BH3 x THF with (tBuPOCOP)IrH2. Reaction of (tBuPOCOP)IrH2 with pinacol borane gave initially complex 2, which is assigned a structure analogous to that of 1 based on spectroscopic measurements. Complex 2 evolves H2 at room temperature leading to the borane complex 3, which is formed cleanly when 2 is subjected to dynamic vacuum. The structure of 3 has been determined by X-ray diffraction and consists of the (tBuPOCOP)Ir core with a sigma-bound pinacol borane ligand in an approximately square planar complex. Compound 3 crystallizes in the space group C2/c (Z = 4) with a = 41.2238 (2) A, b = 11.1233 (2) A, c = 14.6122 (3) A, and V = 6700.21 (19) A(3) (130 K). Reaction of (tBuPOCOP)IrH2 with 9-borobicyclononane (9-BBN) affords complex 4. Complex 4 displays (1)H NMR resonances analogous to 1 and exists in equilibrium with (tBuPOCOP)IrH2 in THF solutions.
Synthetic Metals | 1991
H.H. Wang; K.D. Carlson; Urs Geiser; Aravinda M. Kini; Arthur J. Schultz; Jack M. Williams; Lawrence K. Montgomery; W. K. Kwok; U. Welp; K.G. Vandervoort; S.J. Boryschuk; A.V. Strieby Crouch; J.M. Kommers; Diana M. Watkins; J.E. Schriber; Donald L. Overmyer; D. Jung; J.J. Novoa; M.-H. Whangbo
Abstract The syntheses, structures, selected physical properties, and band electronic structures of three copper (I) dicyanamide halide salts of bis(ethylenedithio)tetrathiafulvalene [κ-(ET) 2 Cu[N(CN) 2 ]X, where X = Cl, Br, and I] are discussed. X-ray crystallographic studies demonstrate that the three derivatives are isostructural. The bromide salt is an ambient pressure superconductor with an inductive onset at 11.6 K and a resistive onset at 12.5 K. κ-(ET) 2 Cu[N(CN) 2 ]Cl exhibits the highest reported superconducting transition temperature (T c = 12.8 K. 0.3 kbar) for an organic superconductor, once a semiconductor-semiconductor transition (42 K) is suppressed. The application of GE varnish or Apiezon N grease to crystals of κ-(ET) 2 Cu[N(CN) 2 ]Cl provides sufficient stress to induce superconductivity at “ambient pressure”. Crystals of the iodide remain metallic to ∼150 K, where they become weakly semiconductive. No sign of superconductivity was detected at pressures (hydrostatic and shearing) up to 5.2 kbar and at temperatures as low as 1.1 K. The band electronic structures of the three salts are essentially identical. The differences in superconducting properties are explained in terms of differences in lattice softness, which are strongly influenced by short C-H…donor and C-H…anion contacts.
Journal of the American Chemical Society | 1986
Arthur J. Schultz; Hau H. Wang; Jack M. Williams; Alain Filhol
In this paper the authors report the existence of a new ordered structural phase, denoted as ..beta..*-(ET)/sub 2/I/sub 3/, at T = 4.5 K and P = 1.5 kbar. To our knowledge, this is the first structural study of an organic superconductor with the sample at a temperature below the onset temperature for superconductivity. The structure of ..beta..*-(ET)/sub 2/I/sub 3/ derived from the data set obtained with the sample below the superconducting transition temperature, at 4.5 K and 1.5 kbar, is completely ordered but is not isostructural with the ..beta..-phase structures of the I/sub 2/Br/sup -/, AuI/sub 2//sup -/, and IBr/sub 2//sup -/ salts.
Physical Review Letters | 2008
V. O. Garlea; Rongying Jin; David Mandrus; Bertrand Roessli; Qingzhen Huang; Martha Miller; Arthur J. Schultz; Stephen E Nagler
Neutron inelastic scattering and diffraction techniques have been used to study the MnV2O4 spinel system. Our measurements show the existence of two transitions to long-range ordered ferrimagnetic states, the first collinear and the second noncollinear. The lower temperature transition, characterized by development of antiferromagnetic components in the basal plane, is accompanied by a tetragonal distortion and the appearance of a gap in the magnetic excitation spectrum. The low-temperature noncollinear magnetic structure has been definitively resolved. Taken together, the crystal and magnetic structures indicate a staggered ordering of the V d orbitals. The anisotropy gap is a consequence of unquenched V orbital angular momentum.
Angewandte Chemie | 2010
Scott R. Daly; Paula M. B. Piccoli; Arthur J. Schultz; Tanya K. Todorova; Laura Gagliardi; Gregory S. Girolami
The concept of coordination number is extremely useful and is widely employed to describe the local chemical environments of atoms. Originally defined by Alfred Werner in 1893, the coordination number is closely related to many other important properties such as atomic radius, molecular and electronic structure, and chemical reactivity. An important modification of Werner s original concept was the recognition that, for certain ligands such as ethylene, two linked atoms jointly occupy a single coordination site. This modified definition is widely used to describe both transitionmetal (d-block) and inner-transition-metal (f-block) complexes. An interesting question is: what is the largest possible coordination number? This question has recently been considered theoretically, and the 15-coordinate ion PbHe15 2+ has been predicted to be a bound species. The complexes tetrakis(cyclopentadienyl)uranium [UCp4] and its thorium analogue [ThCp4] are each connected to 20 atoms, [10] but the Werner coordination number of 12 (counting p bonds as occupying one site) is widely acknowledged to be more appropriate to describe the metal–ligand bonding in these compounds. Very high Werner coordination numbers are seen for metal complexes of the borohydride anion BH4 , which can coordinate to a single metal through as many as three hydrogen atoms. From an electronic perspective, each B-H-M interaction involves a separate electron pair, 14] and each BH-M interaction can be considered as a separate bond. Accordingly, [Zr(BH4)4], [15–17] [Hf(BH4)4], [15,16, 18] [Np(BH4)4], [19] and [Pu(BH4)4], [19] all have coordination numbers of 12, and [Th(BH4)4], [15, 16] [Pa(BH4)4], [19] and [U(BH4)4], [20] all of which are polymers in the solid state, have coordination numbers of 14. Some derivatives of these compounds also have high coordination numbers, such as the 14-coordinate tetrahydrofuran complex [U(BH4)4(thf)2]. [21] No complex of any kind, however, has been definitively shown to adopt a Werner coordination number higher than 14. Herein, we report the synthesis, single-crystal X-ray and neutron diffraction studies, and DFT investigations of the first 15-coordinate complex. DFT calculations suggest that this complex may adopt a 16-coordinate structure in the gas phase. This compound extends our recent studies of a new class of chelating borohydride ligands, that is, the aminodiboranates, some of which form highly volatile complexes that are useful as precursors for the chemical vapor deposition of thin films. Reaction of ThCl4 with four equivalents of sodium N,Ndimethylaminodiboranate, Na(H3BNMe2BH3), in tetrahydrofuran produced [Th(H3BNMe2BH3)4] (1), which could be isolated as colorless prisms by crystallization from diethyl ether. The IR spectrum of 1 contains strong bands at 2420 cm 1 that arise from terminal B–H stretches, and at 2264 and 2208 cm 1 that arise from bridging B-H···Th stretches. For comparison, [Th(BH4)4] contains a strong terminal B–H band at 2530 cm 1 and bridging B-H-M bands at 2270, 2200, and 2100 cm . The H NMR spectrum of 1 (C6D6 at 20 8C) contains peaks at d = 2.11 ppm (s, NMe2) and d = 4.23 ppm (br 1:1:1:1 q, JBH = 90 Hz, BH3); the terminal and bridging B–H units thus exchange rapidly on the NMR time scale. The B NMR spectrum consists of a binomial quartet at d = 2.75 ppm, which arises from coupling of the B nuclei with the three rapidly exchanging H nuclei (JHB = 90 Hz). For comparison, the B spectrum of [Th(BH4)4] consists of a quintet at d = 8.0 ppm (JBH = 86.5 Hz). Single-crystal X-ray and neutron diffraction studies of 1 reveal that it is monomeric with four chelating aminodiboranate ligands. The eight boron atoms describe a distorted D2d dodecahedral structure, in which boron atoms B1, B2, B2A, and B1A describe one planar trapezoidal array, and atoms B3, B4, B5, and B6 describe the other (Figure 1). The B2-Th1B2A and B4-Th1-B6 angles between wingtip boron atoms are almost linear at 172.61(12)8 and 171.85(13)8, respectively. Interestingly, seven of the eight Th···B distances (those for boron atoms B1–B5) range from 2.882(3) to 2.949(3) , but [*] S. R. Daly, Prof. G. S. Girolami School of Chemical Sciences University of Illinois at Urbana-Champaign 600 South Matthews Avenue, Urbana, IL 61801 (USA) Fax: (+ 1)217-244-3186 E-mail: girolami@scs.illinois.edu
Journal of Applied Physics | 2002
Anders Bentien; Bo B. Iversen; J. D. Bryan; Galen D. Stucky; A. E. C. Palmquist; Arthur J. Schultz; R. W. Henning
Multitemperature (15, 100, 150, 200, 300, 450, 600, 900 K) single crystal neutron diffraction data on the type I clathrate Ba8Ga16Si30 are reported. For the framework atoms reciprocal space structural refinements give total occupancies in the unit cell of Ga/Si=3.8/2.2, 1.8/14.2, 10.2/13.8 for the 6c, 16i, and 24k sites respectively, thus showing that Ga avoids the tetrahedral 16i positions. The guest atom displacement parameters obtained from structure factor fitting are analyzed with semianharmonic Einstein models giving Einstein temperatures (ΘE) of 69(1), 98(7), and 124(2) K for Ba(2)(100), Ba(2)[100], and Ba(1), respectively. The analysis furthermore suggests that all guest atoms are structurally disordered, and the disorder appears to be temperature dependent with increased host-guest interaction at high temperatures. The structure factors are subsequently used in the maximum entropy method calculations to obtain direct space nuclear densities. These are modeled with anharmonic one-particle potentia...
Science | 1979
Robert W. Broach; Arthur J. Schultz; Jack M. Williams; George M. Brown; Juan M. Manriquez; Paul J. Fagan; Tobin J. Marks
The structure of an unusual organometallic complex, {Th[(CH3)5C5]2 H(�-H)}2 � C6H5CH3, has been determined from neutron diffraction data, using only the direct-methods program MULTAN. Besides providing accurate metrical information on the first organometallic actinide hydride complex, these results have general and far-reaching implications concerning the complexity and size of crystal structures that can be elucidated solely on the basis of neutron diffraction data.
Angewandte Chemie | 1999
Jacob Overgaard; Birgit Schiøtt; Finn K. Larsen; Arthur J. Schultz; John C. MacDonald; Bo B. Iversen
Low-barrier hydrogen bond (LBHB) involvement in enzyme catalysis is examined by analysis of experimental nuclear and electron densities of a model compound for the catalytic triad in serine proteases (shown schematically), which is based on a cocrystal of betaine, imidazole, and picric acid. The three short, strong N-H⋅⋅⋅O hydrogen bonds in the structure have varying degrees of covalent bonding contributions suggesting a gradual transition to the LBHB situation.
Journal of Applied Crystallography | 2014
Arthur J. Schultz; Mads R. V. Jørgensen; Xiaoping Wang; Ruth Mikkelson; D. Mikkelson; V. E. Lynch; Peter F. Peterson; Mark L. Green; Christina Hoffmann
The intensity of single-crystal Bragg peaks obtained by mapping neutron time-of-flight event data into reciprocal space and integrating in various ways is compared. These methods include spherical integration with a fixed radius, ellipsoid fitting and integration of the peak intensity, and one-dimensional peak profile fitting. In comparison to intensities obtained by integrating in real detector histogram space, the data integrated in reciprocal space result in better agreement factors and more accurate atomic parameters. Furthermore, structure refinement using integrated intensities from one-dimensional profile fitting is demonstrated to be more accurate than simple peak-minus-background integration.