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101.
Dr. Joydeb Goura Dr. Bassem S. Bassil Dr. Jasleen K. Bindra Dr. Iwona A. Rutkowska Prof. Pawel J. Kulesza Prof. Naresh S. Dalal Prof. Ulrich Kortz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15821-15824
The 48-FeIII-containing 96-tungsto-16-phosphate, [FeIII48(OH)76(H2O)16(HP2W12O48)8]36− ( Fe48 ), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {FeIII6P2W12} units that are linked in an end-on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe48 was synthesized by a simple one-pot reaction of an {Fe22} coordination complex with the hexalacunary {P2W12} POM precursor in water. The title polyanion was characterized by single-crystal XRD, FTIR, TGA, magnetic and electrochemical studies. 相似文献
102.
103.
Li-Hua Bi Ulrich Kortz Michael H. Dickman Saritha Nellutla Naresh S. Dalal Bineta Keita Louis Nadjo Manuel Prinz Manfred Neumann 《Journal of Cluster Science》2006,17(2):143-165
The mixed-valence 14-vanadogermanate [GeVV 12VIV 2O40]8? (1) has been synthesized and characterized in solution by 51V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K2Na6[GeVV 12VIV 2O40]·10H2O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) Å, b=11.6205(3) Å, c=20.2658(5) Å, and Z=2. Polyanion 1 is composed of a central GeIVO6 octahedron which is surrounded by a total of 14 VO6 octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two VIV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two VIV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two VIV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a VIV ion, suggesting a possible ground state of $3d_{x^{2}-y^{2}}.The mixed-valence 14-vanadogermanate [GeVV
12VIV
2O40]8− (1) has been synthesized and characterized in solution by 51V-NMR, UV–vis and electrochemistry and in the solid state by IR, magnetism, EPR, XPS and elemental analysis. Single-crystal X-ray analysis was carried out on K2Na6[GeVV
12VIV
2O40]·10H2O (KNa-1), which crystallizes in the orthorhombic system, space group Immm, with a=10.9623(3) ?, b=11.6205(3) ?, c=20.2658(5) ?, and Z=2. Polyanion 1 is composed of a central GeIVO6 octahedron which is surrounded by a total of 14 VO6 octahedra. Vanadium-51 NMR in solution results in three peaks with intensity ratio of 8:4:2 which is in complete agreement with the solid state structure. The presence of two VIV centers was established by UV–vis, electrochemistry, magnetism, EPR, XPS and elemental analysis. Electrochemistry revealed that the two VIV-centers in 1 are oxidized through a single well-defined step, which does not split with changes in scan rate or pH. Polyanion 1 is also an active two-electron oxidation catalyst for the coenzyme NADH at pH 8, unprecedented in polyoxometalate chemistry. Magnetic susceptibility, magnetization and EPR data on KNa-1 complement the X-ray and electrochemistry results by confirming the presence of two unpaired electrons per molecule of 1. The two VIV ions possessing the spin are very weakly coupled, essentially acting as two well-isolated S=1/2 ions. The observed g-value of 1.977 from EPR and magnetic susceptibility measurements is consistent with literature reported value for a VIV ion, suggesting a possible ground state of XPS measurements on KNa-1 also confirmed the coexistence of VV and VIV in 1.Dedicated to Professor Michael T. Pope on the occasion of his retirement. 相似文献
104.
Evan M. Benbow Naresh S. Dalal Susan E. Latturner 《Journal of solid state chemistry》2009,182(11):3055-3062
Binary eutectic mixtures of early lanthanide metals and late transition metals have been explored as media for crystal growth of new intermetallic phases. A large family of R6T13−xAlxMy phases (R=La or Nd; T=Fe or Mn; M=main group elements) with the La6Co11Ga3 structure type can be crystallized from La/Ni and Nd/Fe eutectics. The tetragonal structure of these compounds features slabs of transition metal atoms capped with mixed T/Al sites and separated by layers of lanthanide ions. The growth of large crystals of the lanthanum analogs allows for the study of the anisotropic magnetic properties of the transition metal slabs. For La6Fe13−xAlxMy analogs, these order antiferromagnetically with TN strongly dependent on the Fe/Al ratio on the mixed sites. Growth of Mn analogs is reported for the first time; the transition metal slabs in La6(Mn/Ni)10Al3 phases order ferromagnetically with a TC of 200 K. 相似文献
105.
We report on the minority carrier lifetime, diffusion length and mobility in nanocrystalline Si and (Si,Ge) p+nn+ devices. The devices were fabricated on stainless steel using VHF plasma deposition techniques. Minority carrier lifetime was measured using junction reverse recovery techniques. The minority carrier lifetime was found to be well correlated with the inverse of defect density and increased with increasing measurement temperature. Simultaneous measurement of diffusion length and lifetime yielded values for hole mobility. 相似文献
106.
使用基于Dirac-Hartree-Fock方法的Grasp2K程序包,计算了Am原子及离子的K,L,M-X射线的跃迁能和跃迁速率。在计算中,包括了Breit相互作用、真空极化和自能等重要效应。目前研究结果与已有的其他实验和理论结果相对误差约为0.04%。此外,我们还首次计算了从Am1+到Am6+离子的K,L,M-X射线的跃迁能和跃迁速率。相对于中性原子,来自低离化态的跃迁能相对于中性的相应跃迁线的能量仅有轻微的偏移,这反映出外层电子几乎不影响内壳层的跃迁性质。Transition energies and rates of K, L, and M X-ray lines from electric-dipole transition of americium have been calculated using GRASP2K code based on the Dirac-Hartee-Fock method. The effects of the Breit interaction, vacuum polarization and self energy were taken into account. It is found that the present results agree within 0.04% with other experimental and theoretical values. Furthermore, we also calculated transition energies and rates of the K-, L-, and M-shell hole states of americium ions with charge states Am1+-Am6+ for the first time. It is found that the transition energies and rates change slightly relative to the corresponding results of americium atoms, which indicates that the outermost electrons can hardly affect inner-shell transition properties. 相似文献
107.
Dark energy models which alter the relative scaling behavior of dark energy and matter could provide a natural solution to the cosmic coincidence problem-why the densities of dark energy and dark matter are comparable today. A generalized class of dark energy models is introduced which allows noncanonical scaling of the ratio of dark matter and dark energy with the Robertson-Walker scale factor a(t). We show that determining whether there is a coincidence problem, and the extent of cosmic coincidence, can be addressed by several forthcoming experiments. 相似文献
108.
Antifreeze proteins (AFPs) are a group of structurally very diverse proteins with the unique capability of binding to the surface of seed ice crystals and inhibiting ice crystal growth. The AFPs bind with high affinity to specific planes of the ice crystal. Previously, this affinity of AFPs has been ascribed to the formation of multiple hydrogen bonds across the protein-ice interface, but more recently van der Waals interactions have been suggested to be the dominant energetic factors for the adsorption. To determine whether van der Waals interactions are also responsible for the binding specificities of AFPs, the protein-ice interaction of the helical AFP Type I from winter flounder (HPLC6) was studied using a Monte Carlo rigid body docking approach. HPLC6 binds in the [1102] direction of the [2021] plane, with the Thr-Ala-Asn surface comprising the protein's binding face. The binding of HPLC6 to this ice plane is highly preferred, but the protein is also found to bind favorably to the [1010] prism plane using a different protein surface comprised of Thr and Ala residues. The results show that van der Waals interactions, despite accounting for most of the intermolecular energy (>80%), are not sufficient to completely explain the AFP binding specificity. 相似文献
109.
On the basis of electric field effects on the EPR spectra of Cr5+ centers in KD2AsO4 and KD2PO4, and of a symmetry analysis, we show that the spectra should be interpreted in terms of a four-site exchange process rather than two-site processes as others have done. Using this procedure, we obtain new and more extensive data on the dynamic processes in these crystals show that above Tc the changes in EPR line shape reveal only one type of dynamic process, a polarization fluctuation. 相似文献
110.