Critical behavior of the surface of FeBO3 single crystals

The behavior of the surface and near-surface layers of macroscopic FeBO₃ single crystals is studied over the temperature range from 291 K to Neél temperature (T _N ) using depth-selective conversion-electron Mössbauer spectroscopy. Three different phases or states, namely, an antiferromagnetically ordered phase (similar to the crystal bulk state), a surface phase, and a transition layer between them coexist near the Neél point in a surface layer ～500 nm thick. The critical parameters found for the bulk phase agree well with the theoretical critical index ν_th?0.63 predicted by the 3D Ising model. As the crystal surface is approached, the critical parameter β increases to 0.51(2) but remains smaller than the value of β=0.8 for the surface of a semi-infinite Heisenberg model. Therefore, the effective dimensionality of the system, being equal to 3 in the bulk, decreases at the crystal surface.     

Cycle decompositions of pathwidth-6 graphs

Hajós' conjecture asserts that a simple Eulerian graph on $n$ vertices can be decomposed into at most $\text{◂⌊⌋▸}\lfloor \left(n-1\right)/2\rfloor$ cycles. The conjecture is only proved for graph classes in which every element contains vertices of degree 2 or 4. We develop new techniques to construct cycle decompositions. They work on the common neighborhood of two degree-6 vertices. With these techniques, we find structures that cannot occur in a minimal counterexample to Hajós' conjecture and verify the conjecture for Eulerian graphs of pathwidth at most 6. This implies that these graphs satisfy the small cycle double cover conjecture.     

Trinuclear, antiferromagnetically coupled Cu(II) complex with an EPR spectrum of mononuclear Cu(II): effect of alcoholic solvents

A rigid trinuclear copper pyrazolato framework supports the solvolytic exchange of mu3-X by mu3-OR ligands (X = Cl and Br; R = alkyl group), converting the trinuclear ferromagnetically coupled S = 3/2 system to antiferromagnetically coupled S = 1/2 in the solid state. In contrast, we propose that, in alcoholic solutions, solvolysis results in unsymmetrical coordination of the Cu3 cluster, magnetically decoupling one Cu center from the other two. This disguises the intact triangular Cu(II)3 system as a mononuclear Cu(II) complex in its electron paramagnetic resonance spectrum.     

Triflic acid catalyzed reductive coupling reactions of carbonyl compounds with O-, S-, and N-nucleophiles

Highly efficient metal-free reductive coupling reactions of aldehydes and ketones with a range of nucleophiles in the presence of triflic acid (1-5 mol%) as the catalyst are presented. The reactions can be performed at ambient temperature without exclusion of moisture or air. A range of symmetrical and unsymmetrical ethers were obtained by this method in high yields and short reaction times. For the first time, the influence of additional functionalization has been studied. Furthermore, the formation of thioethers from ketones (by addition of unmodified thiols) and of sulfonamides from either aldehydes or ketones has been achieved under catalytic conditions.     

Di-2-pyridyl ketone oxime in copper chemistry: di-, tri-, penta- and hexanuclear complexes

The use of di-2-pyridyl ketone oxime (Hpko)/X- "blends" (X- = OH-, Cl-, ClO4-) in copper chemistry has yielded neutral binuclear and cationic trinuclear, pentanuclear or hexanuclear complexes. Various synthetic procedures have led to the synthesis of compounds [Cu5(pko)7].[ClO4]3.2CH3OH.2H2O (1), [Cu3(pko)3(OH)(Cl)]2[Ph4B]2.4DMF.2H2O (2), [Cu2(pko)4] (3), {[Cu6(pko)6ClO4(CH3CN)6][Cu6(pko)6(ClO4)3(CH3CN)4]}.8ClO4.14CH3CN.H2O (4). The structures of the complexes have been determined by single-crystal X-ray crystallography.     

MRI investigation of hydration and heterogeneous degradation of aliphatic polyesters derived from lactic and glycolic acids: a controlled drug delivery device.

Magnetic Resonance Imaging experiments have been used to investigate the degradation of drug-loaded poly(glycolic lactic acid) (PGLA) 50:50 cylinders. Spatial variation in the rate of degradation throughout the polymer cross-section has been observed non-invasively using quantitative imaging of penetrant concentration, T(2) and self-diffusion coefficient. This spatial variation in the rate of degradation was attributed to the quicker degradation in the inner region of the sample due to autocatalysis by carboxyl end groups generated upon ester bond cleavage.     

Blue-colored, linear rigid-axle [2]pseudorotaxanes: metal-binding properties, crystal structures, and blue/red dichroism

Rare blue-colored [2]pseudorotaxanes based on the previously unexplored [N,N'-bis(4-pyridyl)-4,4'-bipyridinium](2+) axle and bis(1,5-naphtho)-32-crown-8 (BN32C8) or bis(1,5-naphtho)-38-crown-10 (BN38C10) wheels have been synthesized and characterized by UV-vis, (1)H NMR spectroscopy, and electrochemistry, and their metal-binding properties toward CdI(2) and HgCl(2) have been studied by optical absorption in solution and X-ray crystallography in the solid state. We report contrasting structures of the same metal and different wheels or the same wheel and different metals. We also show for the first time that a simple metal complex, such as Hg(2)Cl(6)(2-), can induce a blue/red linear dichroism by organizing the [2]pseudorotaxane units into a columnar arrangement in the crystal.     

Synthesis and complex formation of thiodiacetic acid-bis(2-pyridylmethylamide)

Summary A new ligand, thiodiacetic acid-bis(2-pyridylmethylamide), has been synthesized and the formation and structures of its complexes with Cu, Ni, Co, Cd and Pt investigated.