Crystal Structure Determination of Thallium Carbodiimide,Tl2NCN

Orange‐red single crystals of thallium carbodiimide, Tl₂NCN, have been grown from an aqueous solution of cyanamide and thallium carbonate under strongly basic conditions. Tl₂NCN crystallizes in space group with a = 5.338(1), b = 6.626(2), c = 9.645(3) Å, α = 98.765(4)°, β = 98.685(4)°, γ = 113.178(4)°, and Z = 3; the structure can be considered a strongly distorted anti‐CdI₂ type. One finds two crystallographically different and irregular [NCN]Tl₆ octahedra in which the Tl–N distances of the three‐coordinate monovalent thallium ions lie between 2.52 and 2.72Å. The two symmetry‐inequivalent NCN^2? units adopt the carbodiimide shape, and the course of its molar volume as a function of the monovalent counter cation is analyzed.     

On singularities of solution of Maxwell's equations in axisymmetric domains with conical points

Boundary value problems (BVP) in three‐dimensional axisymmetric domains can be treated more efficiently by partial Fourier analysis. Partial Fourier analysis is applied to time‐harmonic Maxwell's equations in three‐dimensional axisymmetric domains with conical points on the rotation axis thereby reducing the three dimensional BVP to an infinite sequence of 2D BVPs on the plane meridian domain Ω_a?? of . The regularity of the solutions u _n (n∈?₀:={0, 1, 2,…}) of the two dimensional BVPs is investigated and it is proved that the asymptotic behaviour of the solutions u _n near an angular point on the rotation axis can be characterized by singularity functions related to the solutions of some associated Legendre equations. By means of numerical experiments, it is shown that the solutions u _n for n∈?₀\{1} belong to the Sobolev space H² irrespective of the size of the solid angle at the conical point. However, the regularity of the coefficient u ₁ depends on the size of the solid angle at the conical point. The singular solutions of the three dimensional BVP are obtained by Fourier synthesis. Copyright © 2006 John Wiley & Sons, Ltd.     

Site-preferential design of itinerant ferromagnetic borides: experimental and theoretical investigation of MRh6B3 (M = Fe, Co)

Single-phase polycrystalline samples of the compounds MRh(6)B(3) (M = Fe, Co) as well as single crystals of CoRh(6)B(3) have been synthesized by arc-melting the elements under a purified argon atmosphere in a water-cooled copper crucible. The characterization of the new phases was achieved by using single-crystal and powder X-ray diffraction as well as EDX measurements. The two phases are isotypic and crystallize in the hexagonal Th(7)Fe(3) structure type (space group P6(3)mc, no. 186, Z = 2). In this structure, the magnetically active atoms (Fe, Co) are preferentially found on only one of the three available rhodium sites, and together with rhodium they build a three-dimensional network of interconnected (Rh/M)(3) triangles. Magnetic properties investigations show that both phases order ferromagnetically below Curie temperatures of 240 K (for FeRh(6)B(3)) and 150 K (for CoRh(6)B(3)). First-principles DFT calculations correctly reproduce not only the lattice parameters but also the ground state magnetic ordering in the two phases. These calculations also show that the long-range magnetic ordering in both phases occurs via indirect ferromagnetic coupling between the iron atoms mediated by rhodium. This magnetic structural model also predicts the saturation magnetizations to be 4.02 μ(B) for FeRh(6)B(3) (3.60 μ(B) found experimentally) and 2.75 μ(B) for CoRh(6)B(3). Furthermore, both phases are predicted to be metallic conductors as expected for these intermetallic borides.     

Synthesis and characterization of 3-cyano- and 3-nitroformazans, nitrogen-rich analogues of beta-diketimine ligands

The synthesis and characterization of several formazans containing strong electron-withdrawing substituents (cyano and nitro) in the 3 position of the ligand backbone are described. Reactions of aryldiazonium cations with the conjugated bases of either cyanoacetic acid or nitromethane lead to 1,5-diaryl-3-cyano- or 3-nitroformazans, respectively. When these reactions are carried out in aqueous conditions, the range of aromatic groups is limited by the stability of the diazonium salt. However, 3-nitroformazans containing bulky substituents on the nitrogen atoms (2,6-dimethylphenyl, 2,4,6-trimetyhlphenyl, 2,6-diisopropylphenyl, and 3,5-ditert-butylphenyl) could be made by performing the reactions under nonaqueous and anhydrous conditions. NMR and electronic spectroscopic studies indicate that the 3-nitroformazans exist exclusively as closed ( trans-syn, s-cis) isomers whereas the 3-cyanoformazans exist as mixtures of isomers which are substrate-dependent. The crystal structures of five of the formazans are presented: two 3-nitroformazans, both of which are closed, and three 3-cyanoformazans, two of which are closed and one of which adopts an open ( trans-syn, s-trans) structure. Solid state (diffuse reflectance) spectroscopy has been employed to ascertain the isomeric preferences of the other formazans which could not be crystallographically characterized.