Polar Metal Research Articles

Inverse Faraday Effect in Conducting Crystals Caused by a Broken Mirror Symmetry

We consider how the absence of mirror crystal symmetry influences electron kinetics of polar metals, semiconductors, and asymmetric semiconductor hererostructures, as well as some layered antipyroelectric $\mathrm{high}\ensuremath{-}{T}_{c}$ compounds. We find that illumination of such crystals by circularly polarized infrared light should induce a permanent spin orientation of current carriers in an amount proportional to $i\mathbf{c}(\mathbf{c}\ifmmode \dot{}\else \.{}\fi{}\mathbf{\ensuremath{\epsilon}}\ifmmode\times\else\texttimes\fi{}{\mathbf{\ensuremath{\epsilon}}}^{*})$, where $\mathbf{\ensuremath{\epsilon}}$ is the polarization vector, and $\mathbf{c}$ is a unit vector directed either along the polar or antipyroelectric axis or perpendicular to the semiconductor heterostructure.

Bimetallic complexes

Abstract Bimetallic Zr–Re complexes with bridging C5H4PPh2 ligands (henceforth abbreviated as Cp′) are accessible from the mononuclear zirconocene dichloride Cp′2ZrCl2 (1) and reactive rhenium complexes. The attempted synthesis of a cationic complex from 1 and [Re(CO)3(NCMe)3]BF4 resulted in the formation of the zirconium-free compound [ReCl(CO)3(C10H10(PPh2)2)] (2). 2 is apparently formed by cleavage of the Cp′–Zr bonds followed by intramolecular Diels–Alder addition. The compound was fully characterized including an X-ray crystal structure determination of the CDCl3 solvate (triclinic, space group P 1 (No. 2), a=945.1(5) pm, b=1113.9(6) pm, c=1888.5(10) pm, α=92.36(3)°, β=89.98(3)°, γ=113.49(2)°, V=1.821(2)×109 pm3, Z=2). 1 and the highly reactive `salt' [Re(CO)5FBF3] give the mono-bridged ionic complex [Cp′Cl2Zr(μ-Cp′)Re(CO)5]BF4 (3). The doubly Cp′-bridged complex [Cp′2Cl2ZrReCl(CO)3] (4) may be obtained from 1 and either [Re(CO)5Cl] or, more cleanly, [Re2(μ-Cl)2(CO)6(THF)2]. Reaction of 4 with a stoichiometric amount of LiAlH4 gives the bridging hydride complex [Cp′2ClZr(μ-H)ReH(CO)3] (5). From 5 and NaSMe the analogous methyl thiolate complex 6 was obtained in an NMR tube experiment. Reduction of 4 using sodium amalgam produces the dark blue-green complex [Cp′2ClZr-Re(CO)3] (7) which contains a direct Zr–Re bond. Addition of HCl across this polar metal–metal bond gives two isomeric hydrides [Cp′2Cl2ZrReH(CO)3] (8a, b) in a 1:1 ratio and with fac and mer coordination geometries around rhenium, respectively.

Synthesis of Si and Ti-Si-MCM-48 mesoporous materials with controlled pore sizes in the absence of polar organic additives and alkali metal ions

A new route for the synthesis of Si- and Si-Ti-MCM-48 has been developed which allows these materials to be obtained without using polar organic additives and alkali metal ions; this procedure not only produces more active and selective Ti-MCM-48 oxidation catalysts than those reported before, but also permits the synthesis of MCM-48 with controlled pore diameters.

The design of lubricious oil-in-water emulsions

Oil-in-water emulsions, as used in metal working and fire-resistant hydraulic fluids, often show poor lubricating performance and one reason for this is their inability to form effective elastohydrodynamic films. This paper considers how the composition of an oil-in-water emulsion contributes to its lubricating properties. A key factor in oil-in-water emulsion performance lies in the ability of the dispersed oil droplets to wet polar metal surfaces and thus promote full elastohydrodynamic lubrication, without starvation, up to high speeds. In this paper it is shown how this ability can be quantified in terms of measurable surface chemical parameters. Based on this work, three rules for designing lubricious oil-in-water emulsions are proposed. Where possible (a) the emulsifier concentration used should be just below its critical micelle concentration value, (b) the base oil should be polar and (c) the base oil should be viscous. The first two of these factors will promote oil-phase surface wetting while the third will ensure thick-film formation in the full elastohydrodynamic regime.

Poly(ammonioalkanesulfonate) Blends with Polar Organic Species and Alkali Metal Salts: Structure, Glass Transition and Ionic Conductivity

Because the dipole moment of its zwitterionic side group is very high (μ∼23 D), poly[3-(N,N-diethyl-N-(5-methacryloyoxy-3-oxopentyl)-ammonio) propanesulfonate] affords a unique polar host matrix possessing a strong solvation power towards a variety of polar or ionic guest species. Water, glycerol, liquid ethylammonium nitrate, triethylammoniopropanesulfonate are all good plasticizers with a fairly similar efficiency of ΔTg∼−2°C/mol% of additive, while a dizwitterion behaves as a weak antiplasticizer. The stoichiometric blends of the polyzwitterion with alkali metal salts of low enough lattice energy such as thiocyanates, trifuoromethanesulfonates, iodides, perchlorates, tetrafluoro or tetraphenylborates, are amorphous systems showing a single glass transition, with plasticization or antiplasticization effects depending on the salt nature. Microphase separation systematically occurs in these binary systems but long-range order is observed only in some cases, with development of lamellar (I−) or hexagonal (SCN−) structures. Conductivity increases and the dielectric constant of the material decreases as salt is added. The activation energies of the conductivity are not strongly affected either by the state of the material, glassy or viscoelastic, or by the salt nature. © 1997 John Wiley & Sons, Ltd.

Metal on metal surface replacement of the hip. Experience of the McMinn prothesis.

The historical failure of surface replacement has been due to the production of wear debris with subsequent bone resorption, loosening, and failure. To avoid these problems, a surface replacement using a metal on metal bearing allowing thin components and femoral design and instrumentation to avoid varus alignment has been designed. Two hundred thirty-five joints have been resurfaced with this prosthesis in almost 5 years. There have been no femoral neck fractures and no dislocations. There have been 4 designs differing in the method of fixation. In the press fit group, 6 of 70 hips had to be revised for aseptic loosening. In the cemented group, debonding of the cup occurred in 3 of 43 cases. Six patients had hydroxyapatite coated components and have had excellent clinical outcomes. The current design uses a peripherally expanded hydroxyapatite coated cup and a cemented metal head; 116 of this design have been implanted during a 19-month period with excellent outcome. Despite short followup the authors are hopeful that the combination of a polar metal on metal bearing with appropriate fixation will yield a method of preserving bone stock in the younger patient requiring arthroplasty.

A Chelate‐Amidozirconium Fragment as Building Block for Unsupported Trinuclear ZrM2 Heterobimetallic Complexes (M = Fe, Ru, Co)

Exclusive mono-insertion into one of the polar metal–metal bonds is an apt description of the reaction of thermally stable ZrFe2 and ZrRu2 complexes 1 with methyl isocyanide [Eq. (a); M = Fe, Ru]. Thus surprisingly, the second of the two polar ZrM bonds in 1 as well as the distorted tetrahedral coordination geometry of the Zr atom remain intact. The low degree of steric congestion in 1 is manifest in a rapid rotation about the ZrM bonds that cannot be frozen out even on cooling to 180 K.

The structure of organometals determines cytotoxicity and alteration of calcium homeostasis in HL-60 cells.

There is increasing concern about the degradation and metabolisation as well as the biochemical mechanisms of action of organometallic compounds. They are known to be immunotoxic and/or neurotoxic. Because of their different toxic capacities, the development of a reliable correlation between molecular parameters and biochemical effects, which could be helpful in risk assessment, was an aim of this study. The tested organolead and -tin compounds decrease the viability of human cells in culture in a time- and concentration-dependent manner. Parabolic QSAR(1)(1) The abbreviations used are: TMT, trimethyltin chloride; TET, triethyltin bromide; TPT, tripropyltin chloride; TBT, tri- n-butyltin chloride; DBT, di- n-butyltin dichloride; TEL, triethyllead chloride; DEL, diethyllead dichloride; TML, trimethyllead chloride; TPhL, triphenyllead chloride; QSAR, quantitative structure-activity relationships; TSA, total surface area; MW(ion), ionic molecular weight; fMLP, N-formyl-L-methionyl-L-leucyl-L-phenylalanine; fluo-3, fluo-3 free acid; fluo-3 AM, fluo-3 acetoxymethyl ester; Me(2)SO, dimethyl sulfoxide; PLA(2), phospholipase A(2) (EC 3.1.1.4); FCS, fetal calf serum; HEPES, 4-(2-hydroxy-ethyl)-1-piperazineethanesulfonic acid; EGTA, [ethylene-bis(oxyethylenenitrilo)]tetraacetic acid; [Ca(2+)](i), cytosolic free Ca(2+) concentration models yield an adequate correlation between toxicity expressed as LC(50) and structural parameters like ionic molecular weight (MW(ion)) or total surface area (TSA). Two main chemical attributes of the organometals are probably responsible for such a parabolic relationship: the hydrophobic side chain and the polar metal atom. Furthermore, all tested organometal compounds evoke a persistent increase of the cytosolic free calcium concentration [Ca(2+)](i). This effect is mainly due to an influx from the extracellular space. Further results suggest that Ca(2+) enters the cell via opened calcium channels. Based on the essential role of Ca(2+) within cellular signalling, the perturbation of calcium homeostasis appears to be an important event in final cell killing by organometals and it is most likely that other biochemical mechanisms, e.g. activation of phospholipase A(2), are possibly mediated by an increase of [Ca(2+)](i).

Quantum-Chemical Study of Electrochemical Promotion in Catalysis

We report a first-principles theoretical investigation of electrochemical promotion induced by controlled variation in catalyst-electrode potential of metals interfaced with solid electrolytes. Cluster models of oxygen adsorbed on Cu and Pt metal surfaces with coadsorbed positive and negative ions have been considered. The presence of the ions has been simulated also by using point charges and uniform electric fields. We have analyzed the dependence of the metal work function and of the oxygen adsorption energy on the magnitude of the point charges or of the external electric fields. The theoretical results are compared with temperature-programmed desorption, TPD, and potentiometric work function measurements for oxygen on Pt films supported on ZrO2, an O2- conductor. The theoretical calculations show the same linear dependence of the O bond strength on the metal work function observed experimentally. This linear relationship is found also at the first-order perturbation theory level by taking into account only the purely electrostatic interaction between the field induced by the ions and the polar metal−oxygen bond. This suggests that the change in oxygen desorption energy is largely due to electrostatic effects. In addition to providing a direct explanation for the effect of electrochemical promotion, the present results may also provide a sound theoretical basis for the study and understanding of the role of promoters in heterogeneous catalysis.

Cyclopentadienyl metal teflate (OTeF5) complexes

The [M(cp)2(OTeF5)2](M = Ti, Zr, Hf, Mo or W; cp =η5-C5H5) complexes have been readily prepared in halide–teflate metathesis reactions of [M(cp)2Cl2] with TeF5(OH). They extend the fluoride–teflate analogy to a new class of high-oxidation-state transition-metal complex. The compounds, which have been characterised by a combination of IR, mass spectrometry and multinuclear NMR spectroscopy, are shown to have polar metal–teflate interactions.

Mechanical properties of films from polymer latices

AbstractThe mechanical behavior of latex films is governed by their macromolecular nature as well as by their origin from particles dispersed in an aqueous medium. When monomers of different polarity are copolymerized in emulsion copolymerization, a heterogeneous distribution of the polar groups in the latex and the film can occur, owing to the different water solubilities of the comonomers. Films from these latices in many cases show a two‐phase morphology, first, consisting of the main polymer within the particles and, second, a phase which is concentrated in the interphase between the original particles and which has a strong influence on the mechanical properties of the films. Films from latices with crosslinked particles behave like homogeneous networks in the linear viscoelastic range, i.e. at small strains. Structured networks are found when latex films are interparticularly crosslinked during or after film formation, e.g. by polar bifunctional monomers or metal salts. Tensile tests of films show that the mechanical strength of latex films develops in the last stage of film formation by interdiffusion and entaglement formation across particle boundaries.

Heterodimetallic Complexes with an Unbridged, Polar Metal–Metal Bond

The metal–metal bonds are stable without bridging ligands in the heterodinuclear complexes 1 and 2. The combination of one metal center in a high oxidation state and one in a low oxidation state causes these bonds to be strongly polarized. The reactivity of such systems promises to be interesting–recently the direct insertion of CO2 into the ZrFe and ZrRu bond of related complexes has been achieved. R = p‐tolyl. equation image

Titanium Complexes with Tripodal Amido Ligands: Building Blocks for Stable Bimetallic Coordination Compounds Containing Highly Polar Metal–Metal Bonds

Titanium Complexes with Tripodal Amido Ligands: Building Blocks for Stable Bimetallic Coordination Compounds Containing Highly Polar Metal–Metal Bonds

A collision gradient method to determine the immersion depth of nitroxides in lipid bilayers: application to spin-labeled mutants of bacteriorhodopsin.

Ten mutants of bacteriorhodopsin, each containing a single cysteine residue regularly spaced along helix D and facing the lipid bilayer, were derivatized with a nitroxide spin label. Collision rates of the nitroxide with apolar oxygen increased with distance from the membrane/solution interface. Collision rates with polar metal ion complexes decreased over the same distance. Although the collision rates depend on steric constraints imposed by the local protein structure and on the depth in the membrane, the ratio of the collision rate of oxygen to those of a polar metal ion complex is independent of structural features of the protein. The logarithm of the ratio is a linear function of depth within the membrane. Calibration of this ratio parameter with spin-labeled phospholipids allows localization of the individual nitroxides, and hence the bacteriorhodopsin molecule, relative to the plane of the phosphate groups of the bilayer. The spacing between residues is consistent with the pitch of an alpha-helix. These results provide a general strategy for determining the immersion depth of nitroxides in bilayers.

Magnetite Fe 3O 4(111): surface structure by LEED crystallography and energetics

The atomic structure of the Fe 3O 4(111) surface was determined by means of dynamical low-energy electron diffraction (LEED) after being prepared in two different ways. In a first experiment up to 10 monolayers of well-ordered iron oxide films were grown epitaxially onto Pt(111) substrates. A 1 monolayer thick film forms a hexagonal lattice with a lateral repeat distance of 3.2 Å, 15% larger than the lateral periodicity of Pt(111). Above 1 monolayer coverage the LEED pattern reveals a lateral repeat distance of 3.0 Å, indicating a contraction of the oxide lattice with respect to the first monolayer. This new LEED pattern shows half-order spots and is compatible with (2 × 2) reconstructed FeO(111) and bulk terminated Fe 3O 4(111) surfaces. By applying automated tensor LEED to many possible surface structures of these two iron oxides, 8 monolayer thick films were identified to be magnetite, Fe 3O 4. Auger electron spectroscopy (AES) measurements on these films also reveal a stoichiometry close to that of Fe 3O 4. In a second experiment the (111) surface of an α-Fe 2O 3 single crystal was prepared by Ar + ion bombardment and subsequent annealing. Brief annealing to 900, 1000 and 1200 K in 10 −10 and 10 −6 mbar oxygen creates three different LEED patterns indicating structural transformations occurring in the surface region of this crystal. Prolonged annealing to temperatures between 900 and 1200 K stabilizes the same LEED pattern and gives identical intensity-voltage curves as obtained on the 8 monolayer thick films. Therefore the crystal surface region has been reduced to Fe 3O 4 and has the same surface structure as the epitaxially grown films. X-ray photoelectron spectroscopy (XPS) measurements on this surface also reveal a stoichiometry dose to that of Fe 3O 4. The best fit structure for both preparations corresponds to an unreconstructed, but strongly relaxed, polar (111) surface termination of magnetite that exposes 1 4 monolayer of Fe ions over a distorted hexagonal close-packed oxygen layer and minimizes the number of dangling bonds. The surface relaxations are probably driven by electrostatic forces. Our results indicate that minimization of both the number of dangling bonds and the electrostatic surface energy are important in determining the termination and relaxations of this polar metal oxide surface. The electrostatic surface energetics is qualitatively discussed within general, simple concepts applicable to all ionic crystals.

Photoredox Reactions of Hg(CN)2/[Fe(CN)6]4- and [HgCo2(CN)10]6- Induced by Inner-Sphere Metal to Metal Charge Transfer Excitation

Abstract Incomplexes of the type [(NC)2HgIIN CFeII(CN)5]4- which are formed in aqueous mixtures of Hg(CN)2 and [Fe(CN)6]4- both metals are weakly coupled. Optical metal to metal charge transfer (MMCT) excitation from FeII to HgIIleads to the reduction of HgII to Hg0 an the oxidation of [Fe(CN)6]4- to [Fe(CN)6]3-. In the complex [(NC)5CoI-HgII-CoI(CN)5]6- the m etals are strongly coupled by direct but polar metal metal bonds. MMCT (CoI ￫ HgII) excitation induces the photoredox reaction: [HgCo2(CN)10]6-￫Hg0 + 2[Co(CN)5]3-.

Oxygen and chlorine evolution on niobium-, zirconium- and other metal-nitride amorphous thin film electrodes prepared by the reactive RF sputtering technique

Niobium nitride (NbN x ) and zirconium nitride (ZrN x ) amorphous thin film electrodes, deposited on carbon substrates by the reactive RF sputtering technique, are electrochemically stable in aqueous solutions of pH 0–14, allowing oxygen and chlorine evolution under anodic polarization, while Nb and Zr metal electrodes are easily oxidized and passivated under such anodic conditions. XPS studies show that these nitride electrodes are covered by oxide (or oxy-nitride) layers, approximately only a few nm or less thick, even after prolonged flow of an oxygen evolution current. Amorphous titanium nitride (TiN x ) electrodes prepared in a similar way are rapidly passivated like metallic titanium. Amorphous vanadium nitride (VN x ) electrodes are easily dissolved like vanadium metal. Such a difference in the electrochemical stability between the nitrides cannot be explained by thermodynamic consideration of the materials. It seems that the difference in activation energy for the growth of the oxidized overlayer on the nitride plays an important role. The electrocatalytic activities of the NbN x and ZrN x electrodes for oxygen evolution increase with the pH of the solution, and in strong alkaline solutions they are comparable to or even slightly higher than that of a smooth nickel electrode, which is known to be the best practical electrode for oxygen evolution. The mechanism of the oxygen evolution reaction on the NbN x and ZrN x electrodes is discussed briefly.

New microscopic approach in the theory of adsorbed layers

A microscopic approach is proposed for a self-consistent description of electronic and thermodynamic properties of adlayers. It is based on generalizations of both Bogolubov's microscopic picture developed in the theory of polar metals and the second quantization procedure to a system with uncertainty in some phase states. Composite generalized models of the Anderson-Ising type appearing here are analyzed. The self-consistent description is demonstrated for the simplest composite model.

Influence of Polar Groups and Metal Salts on the Residual Currents of Semiconductor Devices Covered with Polyimides

The residual currents of a modified field effect transistor, covered with polyimides containing amido, imino, and carboxylic acid groups, were measured in order to clarify the phenomena causing increased residual currents when larger amounts of unreacted amidic acid groups remain in the coating polyimide layer. Alkoxysilane agents containing imino and amino groups were coated on the transistor surface in order to evaluate effects of these groups on the current. Influence of alkali and transition metal ions, contained as impurities, on the residual current was analyzed by addition of metal salts to the polyimide. Effects of both metal ions on the residual current were compared with those of polar groups such as amido, imino, amino, carboxylic acid, and amidic acid groups in the polyimides.

Electron-phonon interaction in polar solids with application to the tungsten bronzes

We investigate the interaction between electrons and lattice vibrations in polar solids taking into account their microscopic dielectric properties and constructing in a semi-phenomenological manner the nonlocal dielectric function, ϵ GG'( q). The results of earlier, phenomenological theories, such as the Clausius-Mossotti formula for the macroscopic screening constant and Fröhlich's electron-phonon coupling parameter α are obtained from the RPA dielectric function when the dipole approximation is used to calculate the screening by the strongly localized valence electrons. For polar metals we also consider the screening by the free conduction electrons. We present and discuss the results of the screened electron-phonon interaction as a function of the phonon wavevector q for the sodium tungsten bronzes.