Yb Cations Research Articles

Distorted and inequivalently chargedC60anions inYb2.75C60

Near-edge x-ray absorption measurements from single-phase Yb{sub 2.75}C{sub 60} establish that all of the Yb cations are divalent, meaning that the average negative formal charge of the C{sub 60} anions is 5.5. Extended x-ray absorption fine structure (EXAFS) and Raman measurements also reveal that the C{sub 60} anions are distorted in shape, despite their well-ordered local structure around the Yb cations. These findings are combined with a model to show that the charge transferred from Yb to C{sub 60} is both anisotropically distributed on the anions and inequivalently partitioned among them within the unit cell. In the model, the inhomogeneously distributed transferred charge (which arises from the comparatively greater electron affinity of the C{sub 60} pentagonal faces) interacts strongly with the divalent cations and leads to significant anion distortions. The redistribution of transferred charge is traceable to the three crystallographically different types of C{sub 60} anions that are surrounded by 8, 10, or 12 Yb cations, a situation similar to the inequivalently coordinated and charged O anions in the high-T{sub c} compound YBa{sub 2}Cu{sub 3}O{sub 7}. Additional EXAFS and Raman data from Yb{sub 2.75}C{sub 60} heated above 670{degree}C show the removal of local order around the Yb cations and themore » production of an amorphous carbidic phase containing Yb(III). Our collective results, along with comparisons to analogous fulleride and organometallic compounds, provide insight into the distinctive structural features of Yb{sub 2.75}C{sub 60} and its unique distribution of anion charge. They also have general implications for a variety of other metal-doped fullerides. {copyright} {ital 1997} {ital The American Physical Society}« less

Kommensurable Kompositstruktur des β-YbV4O8 1

Abstract The crystal structure of β-YbV4O8 has been determined using a twinned specimen and refined as a commensurate composite structure including V2O4 framework and Yb cations as substructures. The lattice dimensions for V2O4 are a 1 = 9.030(5) Å, b 1 = 10.72(2) Å, c 1 = 2.876(1) Å, α = 89.911(3)°; those for the Yb substructure are a 2 = a 1, b 2 = b 1 − C 1, c 2 = 2c 1. Both substructures have the space group P21/n11. The three-dimensional framework of V2O4 is isostructural with those of Fe2O4 in CaFe2O4 and Ti2O4 in NaTi2O4. The Yb cations occupy half of the [8]-coordinated sites in the tunnel of the framework running parallel to [001]. α- and β-YbV4O8 are polytypes in which the Yb cations are differently arranged while the V2O4 frameworks are essentially the same.

The high Tc superconductor Bi 2Sr 2CaCu 2O 8 studied by electron microscopy. Influence of the partial substitution of Yb for Ca on the modulated structure

The incommensurate modulation of high-Tc superconductors of the type Bi2Sr2Ca1−yYbyCu2O8+x is characterised by electron diffraction. The results are in favour of an atomic displacive one-dimensional modulation with both transverse and longitudinal components. In a four-dimensional description of the modulated structure, the reflection conditions that are evidenced obey the relation: h+l+m=2n. The partial substitution of Yb cations for Ca proves to affect the electrical properties of these materials. Analysis of compounds having different Yb contents (0≤y≤0.66) reveals that the modulation wave vector decreases with increasing y until y=0.5.

Peptide-lanthanide cation equilibria in aqueous solution. II. Isomorphous replacement and separation of the contact and pseudo-contact contributions to NMR shifts induced by a paramagnetic ion

Labile complexes of Pr, Nd, Eu, Dy, Ho, and Yb cations with L-camosine (β-ala-nylhistidine) have been investigated by NMR in aqueous acidic solution. Paramagnetic bound shifts ( Δ 2) values for all proton resonances have been deduced and in the case of CH 2N and CH 2C protons where no contact shift is observed, isomorphous replacement and effective axial symmetry is confirmed for the Ln 3+ series. For contact shifted nuclei, the separation of contact and pseudo-contact terms has been effected by the use of computed Δ 2 values. From these results it appears that the hyperfine coupling constant ( A i ) cannot be kept identical throughout the lanthanide elements for isostructural complexes.