108,988 research outputs found
Magnetoelectric domains and their switching mechanism in a Y-type hexaferrite
By employing resonant X-ray microdiffraction, we image the magnetisation and
magnetic polarity domains of the Y-type hexaferrite
BaSrMgFeO. We show that the magnetic polarity
domain structure can be controlled by both magnetic and electric fields, and
that full inversion of these domains can be achieved simply by reversal of an
applied magnetic field in the absence of an electric field bias. Furthermore,
we demonstrate that the diffraction intensity measured in different X-ray
polarisation channels cannot be reproduced by the accepted model for the polar
magnetic structure, known as the 2-fan transverse conical (TC) model. We
propose a modification to this model, which achieves good quantitative
agreement with all of our data. We show that the deviations from the TC model
are large, and may be the result of an internal magnetic chirality, most likely
inherited from the parent helical (non-polar) phase.Comment: 9 figure
Assembly, Structure, and Reactivity of Cu\u3csub\u3e4\u3c/sub\u3eS and Cu\u3csub\u3e3\u3c/sub\u3eS Models for the Nitrous Oxide Reductase Active Site, Cu\u3csub\u3eZ\u3c/sub\u3e*
Bridging diphosphine ligands were used to facilitate the assembly of copper clusters with single sulfur atom bridges that model the structure of the CuZ* active site of nitrous oxide reductase. Using bis(diphenylphosphino)amine (dppa), a [CuI4(μ4-S)] cluster with N–H hydrogen bond donors in the secondary coordination sphere was assembled. Solvent and anion guests were found docking to the N–H sites in the solid state and in the solution phase, highlighting a kinetically viable pathway for substrate introduction to the inorganic core. Using bis(dicyclohexylphosphino)methane (dcpm), a [CuI3(μ3-S)] cluster was assembled preferentially. Both complexes exhibited reversible oxidation events in their cyclic voltammograms, making them functionally relevant to the CuZ* active site that is capable of catalyzing a multielectron redox transformation, unlike the previously known [CuI4(μ4-S)] complex from Yam and co-workers supported by bis(diphenylphosphino)methane (dppm). The dppa-supported [CuI4(μ4-S)] cluster reacted with N3–, a linear triatomic substrate isoelectronic to N2O, in preference to NO2–, a bent triatomic. This [CuI4(μ4-S)] cluster also bound I–, a known inhibitor of CuZ*. Consistent with previous observations for nitrous oxide reductase, the tetracopper model complex bound the I– inhibitor much more strongly and rapidly than the substrate isoelectronic to N2O, producing unreactive μ3-iodide clusters including a [Cu3(μ3-S)(μ3-I)] complex related to the [Cu4(μ4-S)(μ2-I)] form of the inhibited enzyme
Preparation and Structures of Crystalline Aromatic Cation-Radical Salts. Triethyloxonium Hexachloroantimonate as a Novel (One-Electron) Oxidant
Triethyloxonium hexachloroantimonate [Et3O+SbCl6-] is a selective oxidant of aromatic donors (ArH), and it allows the facile preparation and isolation of crystalline paramagnetic salts [ArH+•, SbCl6-] for the X-ray structure determination of various aromatic cation radicals. The mechanistic relationship between the Meerwein salt [Et3O+SbCl6-] and the pure Lewis acid oxidant SbCl5 is based on a prior ethyl transfer from oxygen to chlorine within the ion pair
Coordination Chemistry of Perhalogenated Cyclopentadienes and Alkynes. 17. Reaction of Dichloroethyne With Platinum(0) Phosphine Complexes: Formation of a .pi.-Complex, Isomerization to .beta.-Chloroethynyl Complexes, and Syntheses of Diplatinioethyne Derivatives. Molecular Structures of (Ph3P)2Pt(.eta.2-ClC.tplbond.CCl) and Cl(Ph3P)2PtC.tplbond.CPt(PPh3)2Cl
Dichloroethyne ClCECCl reacts with Pt(PPh3)2(C2H4) or Pt(PPh& to give the a-complex
Pt(PPh3)2(+21C=CC1) (l),w hich can be isomerized by prolonged refluxing in toluene to trans-
(Ph3P)zC1Pt-C==CC1 (2). 2 easily undergoes exchange reactions with alkylphosphines and
with halide anions to yield trans-(R3P)2ClPt-C=CCl (R = Et (3)) Bu (4)) and trans-(Ph3P)z-
(X)Pt-C=CCl (X = F (5a), Br (5b), I (5c)), respectively. The alkylphosphine complexes 3
and 4 can also be obtained by reaction of Pt(PR3)4 (R = Et, “Bu) with ClCECCl or from 1 and
the corresponding phosphine. When Pt(PPh&(CzH4) is added to a solution of 3, a dinuclear
complex 6 is formed, in which the C=C-Cl group acts as a a,a-bridging ligand. Upon standing,
oxidative addition of the remaining C-C1 bond occurs and the p-ethynediyl complex trans-
C1(R3P)2Pt-C=C-Pt(PPh3)2C1-Cis (R = Et (7a)) can be obtained. The corresponding
p-ethynediyl complex 7b (R = Ph) is formed directly from 2 and Pt(PPh&(CzH4). 7b isomerizes
upon heating in toluene to the symmetrical all-trans isomer 8. The molecular structures of 1
and 8 were determined by X-ray diffraction (1: C ~ ~ H ~ ~ C ~ Z P ~ Pa ~=C 10H.3Z11C(3~) AZ,, b =
10.392(4) A, c = 33.675(16) A, P = 90.17(3)’, monoclinic, P21/n, 2 = 4. 8: C74H&1zP4Ptz9 a =
12.938(2) A, b = 19.964(3) A, c = 24.844(3) A, P = 96.14(1)’, monoclinic, C2/c, 2 = 4)
Orbital momentum Hall effect in p-doped graphane
It is shown that an electric field applied to p-doped graphane generates a
dissipationless orbital momentum Hall current. In the clean limit the
corresponding Hall conductivity is independent of the concentration of holes.
The Hall effect is related to the -Berry phase accumulated when heavy and
light holes are transported around the degeneracy point in the center of the
Brillouin zone. This also leads to the orbital momentum edge currents in the
equilibrium state, and to the accumulation of the orbital momentum at the edges
when the system is driven out of equilibrium.Comment: RevTeX 4, 4 pages, 2 figures, final versio
Angle-deformations in Coxeter groups
The isomorphism problem for Coxeter groups has been reduced to its
'reflection preserving version' by B. Howlett and the second author. Thus, in
order to solve it, it suffices to determine for a given Coxeter system (W,R)
all Coxeter generating sets S of W which are contained in R^W, the set of
reflections of (W,R). In this paper, we provide a further reduction: it
suffices to determine all Coxeter generating sets S in R^W which are
sharp-angled with respect to R.Comment: 23 pages, 6 figures, submitted to AG
Reversible H_2 Addition across a Nickel−Borane Unit as a Promising Strategy for Catalysis
We report the synthesis and characterization of a series of nickel complexes of the chelating diphosphine-borane ligands ArB(o-Ph_2PC_6H_4)_2 ([^(Ar)DPB^(Ph)]; Ar = Ph, Mes). The [^(Ar)DPB^(Ph)] framework supports pseudo-tetrahedral nickel complexes featuring η^2-B,C coordination from the ligand backbone. For the B-phenyl derivative, the THF adduct [^(Ph)DPB^(Ph)]Ni(THF) has been characterized by X-ray diffraction and features a very short interaction between nickel and the η^2-B,C ligand. For the B-mesityl derivative, the reduced nickel complex [^(Mes)DPB^(Ph)]Ni is isolated as a pseudo-three-coordinate “naked” species that undergoes reversible, nearly thermoneutral oxidative addition of dihydrogen to give a borohydrido-hydride complex of nickel(II) which has been characterized in solution by multinuclear NMR. Furthermore, [^(Mes)DPB^(Ph)]Ni is an efficient catalyst for the hydrogenation of olefin substrates under mild conditions
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