Crystal structures of calcium IV and V under high pressure

High-pressure phases IV and V of calcium discovered in 2005 have the highest superconducting transition temperature of 25 K among all the elements; however, their crystal structures have not been determined. From the x-ray powder diffraction data, both Ca IV and V have been found to form unique and complex structures with a coordination number of 7. They were confirmed to be identical to the theoretical models that were recently predicted [Ishikawa, Phys. Rev. B 77 020101(R) (2008)].     

Effect of intervening structure between CuO2 sheets in heavily Fe-substituted high-Tc superconductor FeSr2YCu2O6+δ

Heavily Fe-substituted Ba₂YCu₃O_6+δ-type compound FeSr₂YCu₂O_6+δ exhibits superconductivity around 60 K, only when it is annealed in N₂ and subsequently in O₂. Cationic distribution in this compound is strongly dependent on ionic radius at the Y site, and its superconducting properties are affected by the cationic distribution. In contrast, although the compound with the substitution of fluorite-type unit for Y has cationic order, it does not exhibit superconductivity. We have analyzed the crystal structure of the compounds with the substitution of other lanthanoid elements for Y and with substitution of fluorite-type unit for Y.     

Force in scf theories

A new force approach is reported in which we improve the wavefunction so that the Hellmann-Feynman theorem is satisfied. A sufficient condition for the Hellmann-Feynman theorem to be satisfied is that the basis set includes AO derivatives ?x_r/?x_rfor any basis x_r. Here we test a procedure in which only the first derivative AOs are added to the “parent” AOs. The results are very encouraging.     

The surjectivity of the canonical homomorphism from singular homology to Cech homology

Let be a locally -connected compact metric space. Then, the canonical homomorphism from the singular homology group to the Cech homology group is surjective. Consequently, if a compact metric space is locally connected, then the canonical homomorphism from to is surjective.

     

Multifractal dimensions for branched growth

A recently proposed theory for diffusion-limited aggregation (DLA), which models this system as a random branched growth process, is reviewed. Like DLA, this process is stochastic, and ensemble averaging is needed in order to define multifractal dimensions. In an earlier work by Halsey and Leibig, annealed average dimensions were computed for this model. In this paper, we compute the quenched average dimensions, which are expected to apply to typical members of the ensemble. We develop a perturbative expansion for the average of the logarithm of the multifractal partition function; the leading and subleading divergent terms in this expansion are then resummed to all orders. The result is that in the limit where the number of particlesn, the quenched and annealed dimensions areidentical; however, the attainment of this limit requires enormous values ofn. At smaller, more realistic values ofn, the apparent quenched dimensions differ from the annealed dimensions. We interpret these results to mean that while multifractality as an ensemble property of random branched growth (and hence of DLA) is quite robust, it subtly fails for typical members of the ensemble.     

Reactions of benzylchlorobis(triphenylphosphine)palladium(II) with dimethyl acetylenedicarboxylate

Benzylchlorobis(triphenylphosphine)palladium(II) reacted with dimethyl acetylenedicarboxylate to give [Pd[C(CO₂Me)=C(CH₂Ph)(CO₂Me)]Cl(PPh₃)₂] (II) and [(Ph₃P)ClPdμ-C(CO₂Me)=C(CO₂Me)PdCl(PPh₃) (III). Complexes II and III reacted with Tl(acac) to afford [PdC(CO₂Me=C(CH₂Ph)(CO₂Me)-(acac)(PPh₃)] and [(Ph₃P)(acac)Pdμ-C(CO₂Me)=C(CO₂Me)Pd(acac)(PPh₃)], respectively.     

Preparation and properties of monoorganoantimony tetrachloride adducts

Several adducts of monoorganoantimony tetrachlorides, RSbCl₄L (R = CH₃, C₆H₅, p-CH₃C₆H₄; L = HMPT, PyO, 4-CH₃PyO, DMSO), were prepared. In the solid state all of these adducts are stable at room temperature. They are monomeric in solution, and the existence of hexacoordinate antimony is indicated. CH₃SbCl₄L (L = PyO, 4-CH₃PyO) exists in two isomeric forms in solution and decomposes above 70° into CH₃Cl and SbCl₃L. CH₃SbCl₄(HMPT) decomposes in a similar manner even at room temperature.     

Anionic NaCl-type frameworks of [Mn(II)(HCOO)(3)(-)], templated by alkylammonium, exhibit weak ferromagnetism

We present the synthesis, characterization by IR, TGA, single crystal X-ray structure and magnetic properties of a novel series of NaCl-type frameworks of [AmineH(+)][Mn(HCOO)(3)(-)], templated by alkylammonium. The anionic NaCl-framework of [Mn(HCOO)(3)(-)] is counter-balanced by the alkylammonium cations located in the cavities of the framework to which they are hydrogen-bonded. The divalent manganese ions have octahedral geometry and are bridged by the formate in an anti-anti mode of coordination. All the compounds exhibit long-range antiferromagnetism below 9 K with a slight non-collinear arrangement of the moments. The canting, likely due to second-order spin-orbit coupling, is via a Dzyaloshinski-Moriya antisymmetric exchange mechanism. A spin-flop is observed in each case at fairly low fields. An orthorhombic to monoclinic transformation was observed for the protonated cyclotrimethyleneamine that is accompanied by localization of the cations into two positions below 240 K from the rapid dynamic flipping of the ring observed at room temperature.