Synthesis, stoichiometry and thermal stability of Zn3N2 powders prepared by ammonolysis reactions

Zn₃N₂ powders were prepared by ammonolysis reactions at 600 °C and examined by thermogravimetric analysis, powder X-ray and neutron diffraction. The powders obtained in this way are unstable in an oxygen atmosphere above 450 °C. In an argon atmosphere, the powders are stable up to their decomposition point at around 700 °C. Structural models obtained from Rietveld refinements against the powder neutron diffraction data indicate that the Zn₃N₂ powders so-prepared have the anti-bixbyite structure and are almost certainly stoichiometric with no compelling evidence of nitrogen vacancies. Further, no evidence was found for aliovalent oxygen substitution at the nitrogen sites. The calculated bond valence sums imply that Zn₃N₂ cannot be described as a 100% ionic compound. The structural findings are supported by photoluminescence measurements that reveal a band gap of approximately 0.9 eV.     

Variable temperature H NMR studies on Grubbs catalysts

Variable temperature ¹H NMR studies were conducted to investigate whether steric congestion is influencing the structural rigidity of (IMesH₂)(PCy₃)(Cl)₂RuCHPh (IMesH₂ = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) in solution. It was shown that both mesityl ligands rotate at about the same rate around the N-Mesityl bonds in the IMesH₂ ligand and that changing the solvent does not significantly alter this rotation. It was found that the increased steric congestion in (IMesH₂)(PCy₃)(Cl)₂RuCHPh compared to (PCy₃)₂(Cl)₂RuCHPh does affect the rates of rotation around the C_alkylidene-Ph bonds. Unusual chemical shift positions were also observed in the low temperature ¹H NMR spectrum for the aromatic proton signals for (IMesH₂)(PCy₃)(Cl)₂RuCHPh and (PCy₃)₂(Cl)₂RuCHPh.     

Blow-up of Critical Besov Norms at a Potential Navier–Stokes Singularity

We prove that if an initial datum to the incompressible Navier–Stokes equations in any critical Besov space \({\dot B^{-1+\frac 3p}_{p,q}({\mathbb {R}}^{3})}\), with \({3 < p, q < \infty}\), gives rise to a strong solution with a singularity at a finite time \({T > 0}\), then the norm of the solution in that Besov space becomes unbounded at time T. This result, which treats all critical Besov spaces where local existence is known, generalizes the result of Escauriaza et al. (Uspekhi Mat Nauk 58(2(350)):3–44, 2003) concerning suitable weak solutions blowing up in \({L^{3}({\mathbb R}^{3})}\). Our proof uses profile decompositions and is based on our previous work (Gallagher et al., Math. Ann. 355(4):1527–1559, 2013), which provided an alternative proof of the \({L^{3}({\mathbb R}^{3})}\) result. For very large values of p, an iterative method, which may be of independent interest, enables us to use some techniques from the \({L^{3}({\mathbb R}^{3})}\) setting.     

Stereospecific construction of substituted piperidines. Synthesis of (-)-paroxetine and (+)-laccarin

Short and efficient enantioselective syntheses of (-)-paroxetine and (+)-laccarin are described based on the highly stereospecific cleavage of C(3)-substituted 1,3-cyclic sulfamidates.     

Vacancy contents and phase equilibria of Ti-substituted MnZn ferrite

Measurement of the divalent iron content in acid dissolved MnZn ferrites, fired in controlled atmospheres at various temperatures and quenched, allows calculation of cation vacancy contents. Addition of Ti⁴⁺ to these ferrites resulted in the introduction of vacancies at the rate of about 0 to 0.3 per Ti⁴⁺ depending on heat treatment conditions. Data are presented whereby the vacancy content with Ti⁴⁺ can be calculated based on the oxygen content of the undoped ferrite as available in the literature. Ti⁴⁺ stabilizes the hexagonal hematite-like structure and the phase boundary is presented as a function of Ti⁴⁺ and temperature. The vacancy contents at the phase boundary in Ti⁴⁺-doped ferrite as a function of temperature are in agreement with those calculated from the literature for undoped MnZn ferrites. Finally, the total oxygen content of coexisting spinel and hexagonal phases is presented.     

tert‐Butyl 5‐methoxy‐3‐pentyl­indole‐1‐carboxyl­ate

The molecule of the title compound, C₁₉H₂₇NO₃, is essentially planar, with all non‐H atoms within 0.2 Å of the nine‐membered indole plane, except for the three tert‐butyl C atoms. The C₅ pentyl chain is in an extended conformation, with three torsion angles of 179.95 (13), 179.65 (13) and −178.95 (15)° (the latter two angles include the C atoms of the C₅ chain only). Three intramolecular C—H⋯Ozdbnd;C contacts are present (C⋯O < 3.05 Å and C—H⋯O > 115°), and an intermolecular C—H⋯Ozdbnd;C contact and π–π stacking complete the intermolecular interactions.     

Glycosylated foldamers to probe the carbohydrate-carbohydrate interaction

The synthesis of a triglycosylated helical foldamer based on a combination of cyclopentyl- and pyrrolidinyl-based amino acids is described. This structure is stable in water, maintaining as it does a series of carbohydrate units in proximity to one another, and represents the basis of a new approach to the study of carbohydrate-carbohydrate interactions.     

Intermolecular hydrogen bonding of the two independent mol­ecules of N‐3,5‐di­nitro­benzoyl‐l‐leucine

The title compound, C₁₃H₁₅N₃O₇, crystallizes as two independent mol­ecules which differ in their conformation. Intermolecular hydrogen bonding between the amide and carboxyl­ic acid groups as N—H?O=C interactions results in the formation of one‐dimensional chains with N?O distances of 2.967 (6) and 3.019 (6) Å. Neighbouring chains are linked by C=O?H—O interactions to form a two‐dimensional network, with O?O distances of 2.675 (6) and 2.778 (6) Å.     

Synthesis Of 5-tert-Butyl Benzo[b]thiophene-2-carboxylic Acid

The title compound was prepared from 4-tert-butyl cyclohexanone in high yield by a simple three step procedure.