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排序方式: 共有115条查询结果,搜索用时 46 毫秒
11.
Three Cu-Ln (Ln = Dy, Gd, Y) dodecanuclear clusters assembled by a novel ligand of the benzoxazole type are reported. The dysprosium cluster exhibits a frequency dependence of the alternating-current susceptibility and hysteresis loop at low temperature, indicating single-molecule-magnet behavior. 相似文献
12.
Erwann Delay 《Advances in Mathematics》2002,168(2):213-224
On an asymptotically hyperbolic Einstein manifold (M,g0) for which the Yamabe invariant of the conformal structure on the boundary at infinity is nonnegative, we show that the operators of Ricci curvature, and of Einstein curvature, are locally invertible in a neighborhood of the metric g0. We deduce in the C∞ case that the image of the Riemann-Christoffel curvature operator is a submanifold in a neighborhood of g0. 相似文献
13.
We construct infinite dimensional families of non-singular stationary space times, solutions of the vacuum Einstein equations
with a negative cosmological constant.
Submitted: December 12, 2005. Accepted: May 22, 2006. 相似文献
14.
We shall show that a complete Riemannian manifold of dimension n with Ric?n−1 and its n-st eigenvalue close to n is both Gromov-Hausdorff close and diffeomorphic to the standard sphere. This extends, in an optimal way, a result of P. Petersen [Invent. Math. 138 (1999) 1] (as a by-product, we fill a gap stated in the erratum [Invent. Math. 155 (2004) 223]). We shall also show that a manifold with Ric?n−1 and volume close to is both Gromov-Hausdorff close and diffeomorphic to a space form Sn/π1(M). This extends results of T. Colding [Invent. Math. 124 (1996) 175] and T. Yamaguchi [Math. Ann. 284 (1989) 423]. 相似文献
15.
Mishra S Jeanneau E Chermette H Daniele S Hubert-Pfalzgraf LG 《Dalton transactions (Cambridge, England : 2003)》2008,(5):620-630
The solvated yttrium iodide precursors [Y(L)(8)]I(3) (L = DMSO or DMF), prepared in situ by stirring YI(3)(Pr(i)OH)(4) in DMSO or DMF, react with CuI in the presence of NH(4)I to give ionic hetero-metallic species [Y(DMSO)(8)][Cu(2)(mu-I)I(4)] (1) and [Y(DMF)(8)][Cu(4)(mu(3)-I)(2)(mu-I)(3)I(2)] (2) in excellent yields. Re-crystallization of 1 from DMF afforded the mixed-solvate complex [Y(DMSO)(6)(DMF)(2)][CuI(3)][I] (3). Compounds 2 and 3 undergo unique crystal-to-crystal transformation via progressive substitution of DMF by water molecules in a confined, solvent-free environment. Thus, crystals of 3 transform into [Y(DMSO)(6)(H(2)O)(2)][CuI(3)][I] (4), whereas a discrete ion-pair assembly of 2 is first converted into a 1-D zig-zag structure [Y(DMF)(6)(H(2)O)(2)](3+)[Cu(7)(mu(4)-I)(3)(mu(3)-I)(2)(mu-I)(4)(I)](1infinity)(3-) (5) and finally into a 2-D sheet containing mixed-valent copper atoms, [Y(DMF)(6)(H(2)O)(3)](3+)[Cu(I)(7)Cu(II)(2)(mu(3)-I)(8)(mu-I)(6)](2infinity)(3-) (6). The bi- and tetrafurcate H-bonding between water ligands on yttrium and iodides of the Cu-I cluster plays a pivotal role in the evolution of structures 4-6. Formation of a wide range of iodocuprate structures in 1-6, from discrete mono-, di- or tetranuclear units to one- and two-dimensional extended arrays, reflects the influence of solvated yttrium cations on the nuclearity and dimensionality of Cu-I clusters. TG-DTA-MS studies and DFT calculations for these complexes have also been carried out in order to determine their thermal stability and have insight about aforesaid transformations. 相似文献
16.
Hardouin J Guénin E Malosse C Caron M Lecouvey M 《Rapid communications in mass spectrometry : RCM》2008,22(15):2287-2300
1-hydroxymethylene-1,1-bisphosphonic acids (HMBPs) are important drugs for the treatment of a variety of bone diseases. Since these compounds have no chromophore, their detection is challenging and mass spectrometry (MS) appears to be an appropriate sensitive tool. Our work deals with the analysis by electrospray ionization tandem mass spectrometry (ESI-MSn) of the well-known nitrogen-containing HMBP alendronate and of three analogues, considered as potential prodrugs. These four molecules share a common structure with different protecting groups on the phosphonic acid and on the amine functions. We describe the dissociation mechanisms of nitrogen-containing HMBPs in positive ion mode and we compare, in negative ion mode, our results with literature data. In both modes, the dissociations are essentially losses of ROH, and of phosphorus-containing species (HPO2, ROP(OH)2 and ROPO(OH)2), where R=H, C6H5, or CH3OC6H5. These fingerprints will be of great value for differentiating alendronate from its potential prodrugs in complex biological mixtures. 相似文献
17.
Solvated yttrium iodide precursors [Y(L)8]I3 [L = dimethylformamide (DMF) or dimethylsulfoxide (DMSO)], prepared in situ by stirring YI3(Pr(i)OH)4 in DMF/DMSO, react with 3 equiv of PbI2 in the presence of NH4I to give novel hybrid derivatives based on either a one-dimensional (1D) straight chain, [Y(DMF)8][Pb3(mu-I)9](1infinity) x DMF (1), or discrete pentanuclear iodoplumbates, [Y(DMSO)8]2[(DMSO)2Pb5(mu3-I)2(mu-I)8I6] (2a). The complex 2a and a closely related [Y(DMSO)8][Y(DMSO)7(DMF)][(DMSO)2Pb5(mu3-I)2(mu-I)8I6] (2b) were obtained in good yield by solution phase transformation of 1 in DMSO under slight different conditions. Derivatives 1 and 2 also undergo unique solid-state transformation in a confined environment of paratone to give 1D polymers based on zigzag iodoplumbate chains; crystals of 1 transform into [Y(DMF)6(H2O)2][Pb3(mu3-I)(mu-I)7I](1infinity) (3) via an exchange reaction, whereas those of 2a and 2b are converted into [Y(DMSO)7][Pb3(mu3-I)(mu-I)7I](1infinity) (4) via a decomposition pathway. The trifurcate H-bonding between water ligands on yttrium cation and iodide of the iodoplumbate anion plays a pivotal role in transforming the straight 1D polymeric Pb-I chain of 1 into a zigzag chain in 3. The thermogravimetry-differential thermal analysis studies indicate that complexes with DMF ligands are thermally more stable than those with DMSO ones, the mixed DMF-H2O ligand complex 3 being the most stable one because of the presence of strong H-bonding. Diffuse-reflectance UV-visible spectral analyses of 1-4 show an optical band gap in the 1.86-2.54 eV range, indicating these derivatives as potential semiconductors. In contrast to non-emissive 3 and 4, derivatives 1, 2a, and 2b show remarkable luminescent emission with peak maxima at 703 nm, assigned as an iodine 5p-lead 6s to lead 6p charge transfer (XM-M-CT). 相似文献
18.
Erwann Jeanneau Nathalie Audebrand Daniel Louër 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1012-1013
Crystals of anhydrous cadmium oxalate, β‐[Cd(C2O4)], have been synthesized hydrothermally and the crystal structure solved using single‐crystal X‐ray diffraction data. The Cd and oxalate ions lie about independent inversion centres. The structure consists of a three‐dimensional framework built from sheets of cadmium octahedra linked together by oxalate groups. 相似文献
19.
Erwann Le Coz Ziyun Zhang Dr. Thierry Roisnel Prof. Dr. Luigi Cavallo Dr. Laura Falivene Prof. Dr. Jean-François Carpentier Dr. Yann Sarazin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3535-3544
Two very rare cases of barium boryloxides, the homoleptic [Ba(OB{CH(SiMe3)2}2)2⋅C7H8] and the heteroleptic [{LONO4}BaOB{CH(SiMe3)2}2] stabilised by the multidentate aminoetherphenolate {LONO4}−, are presented, and their structural properties are discussed. The electron-deficient [Ba(OB{CH(SiMe3)2}2)2⋅C7H8] shows, in particular, resilient η6-coordination of the toluene molecule. Together with its amido parents [Ba{N(SiMe3)2}2⋅thf2] and [Ba{N(SiMe3)2}2]2, this complex catalyses the fast and chemoselective dehydrocoupling of borinic acids R2BOH and hydrosilanes HSiR′3, yielding borasiloxanes R2BOSiR′3 in a controlled fashion. The assessment of substrate scope indicates that, for now, the reaction is limited to bulky borinic acids. Kinetic analysis shows that the rate-limiting step of the catalytic manifold traverses a dinuclear transition state. A detailed mechanistic scenario is proposed on the basis of DFT computations, the results of which are fully consistent with experimental data. It consists of a stepwise process with rate-determining nucleophilic attack of a metal-bound O-atom onto the incoming hydrosilane, involving throughout dinuclear catalytically active species. 相似文献
20.
We construct manifold structures on various sets of solutions of the general relativistic initial data sets. 相似文献