Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.     

A spin-frustrated star-shaped heterotetranuclear CrIIIMnII3 species and its magnetic and HF-EPR measurements

A tetranuclear complex [Cr(III)Mn(II)(3)(PyA)(6)Cl(3)] 1 containing pyridine-2-aldoximato monoanion, PyA, has been structurally and magnetochemically characterized. The compound is a rare example of a tetranuclear star-shaped metal topology containing pyridine-2-aldoximato ligands. Static magnetic studies have demonstrated very weak antiferromagnetic exchange interactions between the paramagnetic centers (S(Cr) = 3/2 and S(Mn) = 5/2) resulting in closely spaced low-lying levels, which undergo splitting and crossing. Preliminary high-field EPR measurements (20 < nu < 388 GHz) indicate the presence of zero-field splitting D of the order of 0.7 cm(-1).     

Rational synthesis of a heterotetranuclear CrIII2CuII2 species using a metaloximate as a building block. A magnetostructural study

The reaction of [Cu(DapdoH(2))2](2+) ions with [Cr(III)L(MeOH)2Br](2+) ions (L = 1,4,7-trimethyl-1,4,7-triazacyclononane; DapdoH(2) = 2,6-diacetylpyridine dioxime) produced in situ in methanol, yielded, in the presence of triethylamine, the complex [L(2)Cr(III)(2)(Dapdo)2(OH)2Cu(II)(2)Br(2)](ClO(4))2. It has been characterized on the basis of elemental analysis, IR spectroscopy and variable-temperature (2-298 K) magnetic susceptibility measurements. The molecular structure established by X-ray diffraction consists of a [Cr(III)(2)(micro-NO)4(micro-OH)2Cu(II)(2)](4+)-core, which can be considered as two edge-sharing triangular CrCu(2)-units. The variable-field variable-temperature magnetic measurements revealed a ground state of S(t) = 2 with uncommon antiferromagnetic exchange interactions between the chromium(III) and copper(II) centers: J(A) = -79 +/- 2 cm(-1), J(B) = -17 +/- 1.7 cm(-1), where J(A) represents the interactions through a combination of oximate (>N-O-) and a hydroxo-bridging, while J(B) is the exchange through only a two-atom oximate (>N-O-) group.     

Reduction of nitrite to NO in an organised triphasic medium by platinum carbonyl clusters and redox active dyes as electron carriers

Artificial electron donors such as leuco methylene blue and leuco safranin O reduce nitrite ion to nitric oxide. The reaction is effected in a U-tube where nitrite ion and dye in two aqueous layers are separated by a layer of dichloromethane (a close model for a biological liquid membrane) that contains the platinum carbonyl cluster ([Bu(4)N]2[Pt12(CO)24], Chini cluster). On passing dihydrogen an electron transfer chain involving dihydrogen, the dye, the clusters and the nitrite ion is initiated. The cluster catalytically reduces the dye in the presence of dihydrogen, the reduced dye migrates across the phase boundaries and in turn reduces the nitrite ions. The resultant nitric oxide in the effluent gas has been identified by its reactions with cobalamine and myoglobin. When safranin O is the dye, an adduct is formed between the reduced dye and NO. It has been identified by spectroscopic techniques and its probable structure investigated by DFT calculations.     

Enhanced Carbon Monoxide Electroreduction to >1 A cm−2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House-of-Cards Scaffolds

Cu catalysts are most apt for reducing CO₍₂₎ to multi-carbon products in aqueous electrolytes. To enhance the product yield, we can increase the overpotential and the catalyst mass loading. However, these approaches can cause inadequate mass transport of CO₍₂₎ to the catalytic sites, which will then lead to H₂ evolution dominating the product selectivity. Herein, we use a MgAl LDH nanosheet ‘house-of-cards’ scaffold to disperse CuO-derived Cu (OD-Cu). With this support-catalyst design, at −0.7 V_RHE, CO could be reduced to C₂₊ products with a current density (j_C2+) of −1251 mA cm⁻². This is 14× that of the j_C2+ shown by unsupported OD-Cu. The current densities of C₂₊ alcohols and C₂H₄ were also high at −369 and −816 mA cm⁻² respectively. We propose that the porosity of the LDH nanosheet scaffold enhances CO diffusion through the Cu sites. The CO reduction rate can thus be increased, while minimizing H₂ evolution, even when high catalyst loadings and large overpotentials are used.     

Two-dimensional center-of-mass diffusion of lipid-tethered poly(2-methyl-2-oxazoline) at the air-water interface studied at the single molecule level

The two-dimensional (2D) center-of-mass diffusion, D, of end-tethered poly(2-methyl-2-oxazoline) (PMOx) lipopolymer chains was studied in a Langmuir monolayer at the air-water interface using wide-field single molecule fluorescence microscopy. In this case, tethering and stabilization of hydrophilic PMOx chains at the air-water interface is accomplished via end-tethering to lipid molecules forming a hydrophobic anchor. To explore the influence of molecular weight, M n, and surface concentration, c s, on lateral mobility, two different PMOx chain lengths of n = 30 and 50 ( n, number of monomer units) were analyzed over a wide range of c s. Using multiparticle tracking analysis of TRITC-labeled PMOx lipopolymers, we found two regimes of lipopolymer lateral mobility. At low c s, D is independent of surface concentration but increases with decreasing n. Here diffusion properties are well described by the Rouse model. In contrast, at more elevated c s, the data do not follow Rouse scaling but are in good agreement with a free area-area model of diffusion. The current study provides for the first time experimental insight into the 2D center-of-mass diffusion of end-tethered polymers at the air-water interface. The obtained results will be of importance for the understanding of diffusion processes in polymer-tethered phospholipid bilayers mimicking biomembranes at low and high tethering concentrations.     

Observation of an organic-inorganic lattice match during biomimetic growth of (001)-oriented calcite crystals under floating sulfate monolayers

Macromolecular layers rich in amino acids and with some sulfated polysaccharides appear to control oriented calcite growth in living organisms. Calcite crystals nucleating under floating acid monolayers have been found to be unoriented on average. We have now observed directly, using in situ grazing incidence X-ray diffraction, that there is a 1:1 match between the monolayer unit cell and the unit cell of the (001) plane of calcite. Thus, sulfate head groups appear to act as templates for the growth of (001)-oriented calcite crystals, which is the orientation commonly found in biominerals.     

Monte Carlo Simulation of Contaminant Transport: I. Long-range Correlations in Fracture Conductivity

We develop a network model of fractures, and use the model to study transport of contaminants by groundwater through natural geological media. The fractures are narrow rectangular channels between large flat parallel plates, which are embedded in the surrounding rock matrix. The fracture-permeabilities and the fracture-widths are obtained from both uniform and fBm distributions. The pressure distribution in the network, and subsequently the velocity of groundwater in each channel, is obtained. The transport problem in an individual fracture is solved in Laplace space using the realized groundwater velocities and network mass conservation. The transform space solutions are then inverted to real time using a fast and efficient inversion algorithm. Monte Carlo simulations are then carried out by repeating the above procedure for a large number of realizations. The main focus of this study is to explore the effects correlated fracture-permeabilities and fracture-widths have on the transport of contaminants. While the primary transport mechanism is convection, we also study such processes as adsorption onto the fracture surface, and radioactive decay. We show how these phenomena, individually and in combination with one another, affect the overall transport process. In addition, we investigate the nature of the mixing zone, and discuss how these results can be helpful in developing remediation techniques for a contaminated site.     

Beta decay of 125Sb and level structures in 125Te

The decay of 2.76y ¹²⁵Sb to levels of ¹²⁵Te has been studied using an HPGe detector for gamma-ray and a mini orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 13 gamma rays and 4 conversion electron lines being reported for the first time. New results also include E1 multipolarity assignments to 3 newly observed transitions and M-shell conversion coefficient for the 109 keV M4 transition. A revised ¹²⁵Te level scheme is constructed using Ritz combination principle. While confirming the existence of 10 well established levels below 700 keV excitation, we introduce 3 other levels at 402.0, 538.6 and 652.9 keV. Interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly introduced 538.6 keV (1/2⁺) and 652.9 keV (3/2⁺) levels are seen as the two missing members of the (s _1/2 ⊗ 2⁺) and (d _3/2 ⊗ 2⁺) sextuplet in the quasiparticle-phonon coupling scheme.