Synthesis and Crystal Structure of a Bixbyite‐Type Solid Solution Zr0.43Er0.57O1.07N0.43

A powder of the composition 40 mol‐% Er₂O₃ and 60 mol‐% ZrO₂ has been prepared. The anion deficient fluorite related compound Zr₃Er₄O₁₂ [R\bar{3} : a = 971.79(7) pm and c = 907.976(0) pm] was produced. This precursor was treated with gaseous ammonia at temperatures between 25 and 1200 °C. The reaction was followed in situ by X‐ray diffraction in a high temperature reaction chamber under a constant flow of ammonia. The nitridation of Zr₃Er₄O₁₂ led to a nitride oxide of the solid‐solution‐type with an apparent composition Zr_0.43Er_0.57O_1.07N_0.43 The compound crystallizes isostructural to bixbyite due to vacancy ordering [Ia\bar{3} : a = 1036.37(4) pm]. The reoxidation of the nitride oxide was monitored in DTA/TG experiments exhibiting an almost complete reoxidation to the starting composition except for some inclusions of dinitrogen.     

On the HSAB based estimate of charge transfer between adsorbates and metal surfaces

The applicability of the HSAB based electron charge transfer parameter, ΔN, is analyzed for molecular and atomic adsorbates on metal surfaces by means of explicit DFT calculations. For molecular adsorbates ΔN gives reasonable trends of charge transfer if work function is used for electronegativity of metal surface. For this reason, calculated work functions of low Miller index surfaces for 11 different metals are reported. As for reactive atomic adsorbates, e.g., N, O, and Cl, the charge transfer is proportional to the adatom valence times the electronegativity difference between the metal surface and the adatom, where the electronegativity of metal is represented by a linear combination of atomic Mulliken electronegativity and the work function of metal surface. It is further shown that the adatom-metal bond strength is linearly proportional to the metal-to-adatom charge transfer thus making the ΔN parameter a useful indicator to anticipate the corresponding adsorption energy trends.     

DFT study of a weakly pi-bonded C2H4 on oxygen-covered Ag(100)

The coadsorption of ethylene, C2H4, and atomic oxygen on Ag(100) was studied using density-functional theory. As for the adsorption of oxygen alone, the on-surface hollow sites are predicted to be the most stable adsorption sites at low coverage (< or =1/2 ML). Above this coverage, mixed on-surface + subsurface oxygen configurations become more stable. The binding of ethylene to the clean Ag(100) is weak and little affected by oxygen when it is adsorbed on-surface. On the other hand, we find that the adsorption energy of C2H4 may increase considerably when oxygen is adsorbed into subsurface sites. Our results indicate that the increased reactivity of surface Ag atoms is because of their decreased coordination due to the push out effect of oxygen underneath, more than to their oxidation.     

N2 emission-channel change in NO reduction over stepped Pd(211) by angle-resolved desorption

A sharp change in the N₂ emission channel from N₂O(a) → N₂(g) + O(a) to N(a) + N(a) → N₂(g) has been found at around 500 K in a steady-state NO + D₂ reaction over stepped Pd(211) = [(S)3(111) × (100)] by means of angle-resolved desorption. The desorbing N₂ is highly collimated at around 30° off normal toward the step-down direction below about 500 K due to the intermediate N₂O decomposition, whereas, above 500 K, the near normally directed desorption due to the recombination of N(a) is relatively enhanced. The N₂O decomposition channel is promoted when the reaction is carried out with hydrogen (deuterium) and the channel change is accelerated by quick changes of the amounts of surface hydrogen and oxygen (or NO(a)) into the opposite directions, and enhanced nitrogen removal as ammonia on the resultant hydrogen-rich surface. In the steady-state NO + CO reaction, the N₂ emission channel gradually changes above 500 K toward recombination. A model for the off-normal N₂ emission is briefly described.     

Cycloaddition routes to polycyclic quinones: part 1 boron triacetate as a regiochemical directing agent

9-Hydroxy-1,4-anthraquinone, a benzannelated juglone derivative, undergoes regiospecific cycloaddition with isoprene when conducted in the presence of boron triacetate. The structure of this regiomer has been determined by X-ray crystallography.     

Application of aza-transfer to organic compounds : Reactions between heterocyclic diazo compounds and hydrazines

Aza-transfer reactions between heterocyclic hydrazines and diazonium salts or between heterocyclic diazo compounds and substituted hydrazines have been investigated. The reaction proceeds via intermediate tetrazenes and labelled compounds have been used to elucidate the reaction mechanism.     

Behind the Masks: Identifying Students' Competencies for Learning Mathematics and Science in Urban Settings

Three mathematics and science educators reexamine and reflect on their teaching within the context of the American Association for the Advancement of Sciences (AAAS) and National Council of Mathematics' call to make math and science education accessible to all. The paper highlights the importance of teachers reflecting on their teaching practices in order to create opportunities for their students especially those in the urban setting. The educators argue that teachers' reflection on their teaching can cause them to recognize and validate their students' ways of knowing as they identify the students' hidden/concealed abilities that are often masked by their behaviors. The educators discuss their experiences and highlight the lessons that they learned about ways to prepare teachers to successfully teach math and science students in urban settings. Culturally responsive pedagogy and cultural competency are critical skills that teachers need to develop in order to teach all children, especially those in the math and science classroom in the urban setting.     

The x-ray crystal structure,resolution and absolute configuration of thecis-α-dichloro(1, 8-diamino-3, 6-diazaoctane)-ruthenium(III) cation

Summary Acis- configuration for the [RuCl₂(trien)]Cl·2H₂O (trien=1, 8-diamino-3, 6-diazaoctane) complex has been confirmed by an x-ray crystal structure determination. Crystals are monoclinic, space group P2₁/c witha=7.336 (1),b=8.477 (2),c=23.181 (4) Å, =103.3 (1)°, U=1403 (1) Å.³ Z=4 and M=389.7, D_c=1.84 g cm^–3. The structure was refined by full matrix least squares methods to final residual values of R=0.025 and R_w=0.033 on the basis of 3882 unique reflections. The complex has been resolved into its optical isomers using the (+)1, 2-diaminoethanebis(oxalato)cobaltate(III) anion and the absolute configuration assigned.     

Crystal structure of di-μ-methoxo-bis(chloro-2-methylpyridine copper(II))

The crystal structure of di--methoxo-bis(chloro-2-methylpyridine copper(II)), [CuCl(OCH₃)-(2-mepy)]₂, has been determined from three-dimensional, photographically recorded X-ray data. The unit cell is monoclinic, space groupP2₁/c, with dimensionsa = 8·79,b = 6·01,c = 17·59 Å, = 104·4° and contains two centrosymmetric dimeric units [CuCl(OCH₃). (2-mepy)]₂, in which the copper atoms are linked by methoxide oxygen bridges, the dimers being joined into infinite chains through long copper-chlorine bonds. The environment of each copper atom may be described as a distorted tetragonal pyramid with one chlorine, one nitrogen and two oxygen atoms in the base and a chlorine atom from an adjacent dimer at the apex.