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71.
Pope SJ Burton-Pye BP Berridge R Khan T Skabara PJ Faulkner S 《Dalton transactions (Cambridge, England : 2003)》2006,(23):2907-2912
Luminescent lanthanide complexes have been prepared by exploiting the interaction between lanthanide DO3A complexes and chromophore bearing carboxylates or phosphonates. This interaction can be utilised to probe the choice of sensitising chromophore suited to a given lanthanide. Furthermore, ternary complexes obtained from chromophore appended carboxylates dissociate in the presence of phosphate, while those obtained from phosphonates do not. 相似文献
72.
Reaction of uranium salts with several lacunary polyoxotungstate anions yields four new heteropolyanion assemblies in which the uranium atoms occupy pentagonal bipyramidal coordination polyhedra. Treatment of A,-[SiW9O34]10– with UO2(NO3)2 leads to Na14[Na2(UO2)2(SiW9O34)2]38H2O (1, Monoclinic, P21/c, a=16.5719(8) Å, b=14.1689(7) Å, c=21.2528(10) Å, =111.6670(10)°, V=4786.6(4) Å3, Z=2) which proves to be isostructural with the analogous derivative of [PW9O34]9– reported previously. Solutions of 1 exhibit the 5-line W-NMR spectrum expected for the structure of C
i
point symmetry. The salt (NH4)17[(UO2)3(H2O)4As3W26O94]16H2O (2, Orthorhombic, Pnma, a=40.1747(2) Å, b=18.25840(10) Å, c=18.0817(2) Å, V=13263.4(2) Å3, Z=4) was isolated in 64% yield from a reaction of UO2(NO3)2 with B,-[AsW9O33]9–. The structure of the anion in 2 has C
s
symmetry and contains one -AsW9O33 and two novel -AsW8O30 units linked by the UO2+
2 groups; an additional WO6 links the two AsW8 fragments. Spectrophotometric titration of UCl4 with the sodium salt of [As4W40O140]28– indicated the formation of a 4:1 U:As4W40 complex. During attempts to isolate a crystalline product from this reaction the uranium became oxidized and a guanidinium salt of [Na(UO2)3(OH)(H2O)6As4W40O140(WO)]18– (3, Orthorhombic, Fdd2, a=54.848(3) Å, b=80.809(4) Å, c=20.2874(2) Å, V=89919(7), Z=16) was isolated. The partially disordered structure of 3 shows the S2 and adjacent sites of the lacunary As4W40 anion to be occupied by three UO5 and one WO5 polyhedra. A tetrameric assembly of -SiW10 units linked by UO2+
2 groups occurs in [{M(OH2)}4(UO2)4(OH)2(SiW10O36)4]22– (lithium salt, M=Na, 4a, tetragonal, P42/nmc, a=b=26.5285(2) Å, c=15.0463(2) Å, V=10589.0(2) Å3, Z=2; sodium-potassium salt, M=K, 4b, orthorhombic, Fddd, a=24.180(5) Å, b=31.696(6) Å, c=58.012(12) Å, V=44460(15) Å3, Z=8). Tungsten-183 NMR spectra show the slow transformation of the expected 5-line (1:1:1:1:1) spectrum of 4a to a new species giving a 6-line spectrum (2:2:2:1:2:1). The latter complex has not been successfully isolated. 相似文献
73.
Co-crystallization of K2[Ru(bipy)(CN)4] with lanthanide(III) salts (Ln = Pr, Nd, Gd, Er, Yb) from aqueous solution affords coordination oligomers and networks in which the [Ru(bipy)(CN)4]2- unit is connected to the lanthanide cation via Ru-CN-Ln bridges. The complexes fall into two structural types: [{Ru(bipy)(CN)4}2{Ln(H2O)m}{K(H2O)n}] x xH2O (Ln = Pr, Er, Yb; m = 7, 6, 6, respectively), in which two [Ru(bipy)(CN)4]2- units are connected to a single lanthanide ion by single cyanide bridges to give discrete trinuclear fragments, and [{Ru(bipy)(CN)4}3{Ln(H2O)4}2] x xH2O (Ln = Nd, Gd), which contain two-dimensional sheets of interconnected, cyanide-bridged Ru2Ln2 squares. In the Ru-Gd system, the [Ru(bipy)(CN)4]2- unit shows the characteristic intense (3)metal-to-ligand charge transfer luminescence at 580 nm with tau = 550 ns; with the other lanthanides, the intensity and lifetime of this luminescence are diminished because of a Ru --> Ln photoinduced energy transfer to low-lying emissive states of the lanthanide ions, resulting in sensitized near-infrared luminescence in every case. From the degree of quenching of the Ru-based emission, Ru --> Ln energy-transfer rates can be estimated, which are in the order Yb (k(EnT) approximately 3 x 10(6) sec(-1), the slowest energy transfer) < Er < Pr < Nd (k(EnT) approximately 2 x 10(8) sec(-1), the fastest energy transfer). This order may be rationalized on the basis of the availability of excited f-f levels on the lanthanide ions at energies that overlap with the Ru-based emission spectrum. In every case, the lifetime of the lanthanide-based luminescence is short (tens/hundreds of nanoseconds, instead of the more usual microseconds), even when the water ligands on the lanthanide ions are replaced by D2O to eliminate the quenching effects of OH oscillators; we tentatively ascribe this quenching effect to the cyanide ligands. 相似文献
74.
75.
76.
Zhuyin Ren Stephen B. Pope John M. Guckenheimer 《Proceedings of the Combustion Institute》2007,31(1):473-481
A new dimension-reduction method, the Invariant Constrained-equilibrium Edge Pre-Image Curve (ICE-PIC) method, to simplify chemical kinetics has recently been developed by Ren et al. [Z. Ren, S.B. Pope, A. Vladimirsky, J.M. Guckenheimer, J. Chem. Phys. 124 (2006) 114111]. In the present work, the ICE-PIC method is first applied to the homogeneous autoignition of stoichiometric methane/air and its accuracy is shown to compare favorably to those of other methods (QSSA and RCCE). For inhomogeneous systems such as flames, spatial transport by molecular diffusion causes a small perturbation of the composition away from the attracting, low-dimensional, invariant manifold identified by the ICE-PIC method. A “close-parallel” assumption is introduced which allows this perturbation to be determined, and leads to an additional “transport coupling” term in the evolution equation for the reduced variables. For the test case of a steady, one-dimensional, laminar, methane/air flame, it is shown that the inclusion of transport coupling can reduce the dimension-reduction errors by a factor of 100. The ICE-PIC method with eight degrees of freedom (including transport coupling) exhibits comparable accuracy to a quasi-steady state assumption (QSSA) reduced mechanism with 12 degrees of freedom. 相似文献
77.
78.
We obtain infinite classes of new Einstein-Sasaki metrics on complete and nonsingular manifolds. They arise, after Euclideanization, from BPS limits of the rotating Kerr-de Sitter black hole metrics. The new Einstein-Sasaki spaces L(p,q,r) in five dimensions have cohomogeneity 2 and U(1) x U(1) x U(1) isometry group. They are topologically S(2) x S(3). Their AdS/CFT duals describe quiver theories on the four-dimensional boundary of AdS(5). We also obtain new Einstein-Sasaki spaces of cohomogeneity n in all odd dimensions D = 2n + 1 > or = 5, with U(1)(n + 1) isometry. 相似文献
79.
We obtain an exact solution of the supergravity equations of motion in which the four-dimensional observed Universe is one of a number of colliding D3 branes in a Calabi-Yau background. The collision results in the ten-dimensional spacetime splitting into disconnected regions, bounded by curvature singularities. However, near the D3 branes the metric remains static during and after the collision. We also obtain a general class of solutions representing p-brane collisions in arbitrary dimensions, including one in which the universe ends with the mutual annihilation of a positive-tension and a negative-tension 3 brane. 相似文献
80.
Summary Employing an approximate method the input impedance of a ground based vertical radiator is calculated. The ground system consists
of a number of radial conductors buried just below the surface of the soil. The integrals involved in the solution are evaluated,
in part, by graphical methods. The final results are plotted in a convenient form to illustrate the dependence of the impedance
on number and length of radial conductors for a specified frequency, antenna height, and ground conductivity. It is finally
shown that under usual conditions the radiated fields are modified by only a few percent due to the presence of the ground
system.
Work carried out under Project No. D 48-95-55-07. Paper presented at the U.S.A. National Convention of the Institute of Radio
Engineers in New York, March 1954. 相似文献