A highly reduced vanadium(III/IV) polyoxovanadate comprising an octavanadyl square-prism surrounding a dimetallic vanadium(III) fragment

The synthesis, crystal structure and preliminary magnetic studies are reported for a very highly reduced, VIV8VIII2, polyoxo(alkoxo)vanadate with a unique square prismatic topology.     

Lanthanide discs chill well and relax slowly

The synthesis, structure and magnetic properties of two isostructural heptametallic lanthanide discs are reported, showing single molecule magnet (SMM) behaviour with a large energy barrier for the dysprosium analogue and a large magnetocaloric effect (MCE) for the gadolinium analogue.     

Measurement of material nonlinearity using surface acoustic wave parametric interaction and laser ultrasonics

A dual frequency mixing technique has been developed for measuring velocity changes caused by material nonlinearity. The technique is based on the parametric interaction between two surface acoustic waves (SAWs): The low frequency pump SAW generated by a transducer and the high frequency probe SAW generated and detected using laser ultrasonics. The pump SAW stresses the material under the probe SAW. The stress (typically <5 MPa) is controlled by varying the timing between the pump and probe waves. The nonlinear interaction is measured as a phase modulation of the probe SAW and equated to a velocity change. The velocity-stress relationship is used as a measure of material nonlinearity. Experiments were conducted to observe the pump-probe interaction by changing the pump frequency and compare the nonlinear response of aluminum and fused silica. Experiments showed these two materials had opposite nonlinear responses, consistent with previously published data. The technique could be applied to life-time predictions of engineered components by measuring changes in nonlinear response caused by fatigue.     

Liquid|liquid|electrode triple-phase boundary photovoltammetry of pentoxyresorufin in 4-(3-phenylpropyl)pyridine

Voltammetric responses of pentoxyresorufin in 4-(3-phenylpropyl)-pyridine (PPP) microdroplets immersed in aqueous electrolyte are investigated in the absence and in the presence of light. The reduction of pentoxyresorufin to leuco-pentoxyresorufin in the dark is shown to occur in a two-electron, two-proton process sensitive to the aqueous pH and the PPP|aqueous electrolyte interfacial tension. No significant net photoelectrochemical current responses are observed, although transient responses indicative of distinct electron and hole charge carriers are seen in the presence of pentoxyresorufin. EPR evidence confirms the formation of radical intermediates upon illumination. As a coreactant, duroquinone in the PPP microdroplet phase is investigated and also shown to undergo two-electron, two-proton reduction (to duroquinol) without significant photoelectrochemical activity. When investigated in combination, pentoxyresorufin acts as a photocatalyst for the oxidation of duroquinol to duroquinone. Wavelength-resolved photovoltammetry experiments clearly implicate pentoxyresorufin as the primary photoexcited intermediate. The photoelectrochemical mechanism is explained on the basis of the presence of a long-lived (possibly charge-separated) photoexcited intermediate in the PPP microphase. Implications for light-energy harvesting are discussed.     

Spectroscopic evidence for the direct coordination of the pertechnetate anion to the uranyl cation in [UO2(TcO4)(DPPMO2)2]+

We report the synthesis and structural characterization of [UO(2)(ReO(4))(DPPMO(2))(2)][ReO(4)] and [UO(2)(Cl)(DPPMO(2))(2)][Cl] (where DPPMO(2) = bis(diphenylphosphino)methane dioxide). In both complexes, the linear uranyl dication is coordinated to two bidentate DPPMO(2) ligands in the equatorial plane with one coordinated and one non-coordinated anion (either perrhenate or chloride). We have also prepared the pertechnetate analogue, and, through (31)P and (99)Tc NMR, we have shown that the cation, [UO(2)(TcO(4))(DPPMO(2))(2)](+), is stable in solution.     

Trivalent lanthanide lacunary phosphomolybdate complexes: a structural and spectroscopic study across the series [Ln(PMo11O39)2]11-

We report the syntheses and crystal structures of (NH4)11[Ln(III)(PMo11O39)2.xH2O (where Ln = every trivalent lanthanide cation except promethium) in which two lacunary [PMo11O39]7- anions sandwich an 8-coordinate Ln(III) cation to yield the complex anion, [LnIII(PMo11O39)2]11-. The 14 salts crystallise in two different space groups, C2/c or P1, but the LnIII containing anions are isostructural across the whole series, a very rare example of such a complete study. Solid state and solution 31P NMR, Raman and IR spectroscopies have been used to prove the stability of [Ln(PMo11O39)2]11- in aqueous solution. As expected, the LnIII cation contracts across the series and the Ln-O bond distances decrease uniformly. Interestingly, the splitting in the nu(P-O) mode within the [PMo11O39]7- unit increases uniformly across the series, which we attribute to the stronger interaction with the smaller, higher charge density LnIII cation as the series is traversed. For the 31P NMR measurements a direct comparison of Lanthanide Induced (paramagnetic) Shift could be made with the analogous [P(W11O39)2]11- complexes.     

A novel zirconium polyoxometalate compound: (NH4)9[Zr2(μ‐OH)(H2O)2(AsOH)2(AsW7O28)(AsW10O36)]·26H2O

The crystal structure of the title compound, nona­ammonium (arsenic decatungstido)(arsenic heptatungstido)­di­aqua‐μ‐hydroxo‐(hydroxy­arsenido)­di­zir­conium hexa­cosa­hydrate, which was ob­tained from the reaction of [NaAs₄W₄₀O₁₄₀]²⁷⁻ with Zr^IV, has been determined. The anionic complex consists of two hydroxyl‐bridged seven‐coordinate capped trigonal‐prismatic zirconium ions, which are bonded to an [AsW₁₀O₃₆]⁹⁻ anion and to an [AsW₇O₂₈]¹¹⁻ anion that has two {AsOH}²⁺ capping units. The asymmetric unit contains half of the complex, with one crystallographically independent Zr atom. Crystallographic m symmetry imposed by the monoclinic C2/m space group gives rise to the asymmetric unit comprising half of the complex with one crystallographically independent Zr atom.     

Synthesis and Structural, Magnetic and EPR Characterization of Discrete Finite Antiferromagnetic Chains

The synthesis, magnetic and electron paramagnetic resonance (EPR) characterisation of isolated, discrete, {Cr _n ^III } antiferromagnetically coupled chain complexes is reported for n = 6 and 7. Previous studies had reported supramolecular linked {Cr _n ^III } _x species. For n = 6, the lowest lying total spin state is diamagnetic with S = 1 and 2 first and second excited states, respectively; for n = 7, the lowest lying total spin state is S = 3/2 with S = 1/2 and 5/2 first and second excited states, respectively. The zero-field splittings of these states are well defined by low-temperature, multi-frequency EPR spectroscopy.     

基于相关性的中红外温度与发射率分离算法

温度和发射率是耦合在一起的.在精确获得大气参数的情况下,由传感器的辐射测量反演地表的温度与发射率,仍然是一个病态问题,必须采取一定的策略进行温度与发射率的分离.因此,温度与发射率的分离是红外遥感的核心问题.文章在分析无太阳直射光影响时大气下行辐射和含有大气残留的地表发射率之间关系的基础上,提出了一个针对野外测量中红外高光谱数据的温度与发射率分离算法.该算法利用大气下行辐射和含有大气残留的地表发射率之间的相关性作为判据来优化地表温度,进而获得地表发射率.基于模拟的中红外高光谱数据,对算法的精度进行评价.结果表明,该算法能够获得较高的地表温度和发射率反演精度;具有较广的适用范围,对测量过程中大气下行辐射变化不敏感;同时算法具有一定的抗噪性.     

Redox non-innocence of thioether macrocycles: elucidation of the electronic structures of mononuclear complexes of gold(II) and silver(II)

The mononuclear +2 oxidation state metal complexes [Au([9]aneS(3))(2)](2+) and [Ag([18]aneS(6))](2+) have been synthesized and characterized crystallographically. The crystal structure of the Au(II) species [Au([9]aneS(3))(2)](BF(4))(2) shows a Jahn-Teller tetragonally distorted geometry with Au-S(1) = 2.839(5), Au-S(2) = 2.462(5), and Au-S(3) = 2.452(5) A. The related Ag(II) complex [Ag([18]aneS(6))](ClO(4))(2) has been structurally characterized at both 150 and 30 K and is the first structurally characterized complex of Ag(II) with homoleptic thioether S-coordination. The single-crystal X-ray structure of [Ag([18]aneS(6))](ClO(4))(2) confirms octahedral homoleptic S(6)-thioether coordination. At 150 K, the structure contains two independent Ag(II)-S distances of 2.569(7) and 2.720(6) A. At 30 K, the structure retains two independent Ag(II)-S distances of 2.615(6) and 2.620(6) A, with the complex cation retaining 3-fold symmetry. The electronic structures of [Au([9]aneS(3))(2)](2+) and [Ag([18]aneS(6))](2+) have been probed in depth using multifrequency EPR spectroscopy coupled with DFT calculations. For [Au([9]aneS(3))(2)](2+), the spectra are complex due to large quadrupole coupling to (197)Au. Simulation of the multifrequency spectra gives the principal g values, hyperfine (A) and quadrupole (P) couplings, and furthermore reveals non-co-incidence of the principal axes of the P tensor with respect to the A and g matrices. These results are rationalized in terms of the electronic and geometric structure and reveal that the SOMO has ca. 30% Au 5d(xy)() character, consistent with DFT calculations (27% Au character). For [Ag([18]aneS(6))](2+), detailed EPR spectroscopic analysis confirms that the SOMO has ca. 26% Ag 4d(xy)() character and DFT calculations are consistent with this result (22% Ag character).