The Gallides SrRh2Ga2, SrIr2Ga2, and Sr3Ir4Ga4

The gallides SrRh₂Ga₂, SrIr₂Ga₂, and Sr₃Rh₄Ga₄ were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single‐crystal X‐ray diffraction: CaRh₂B₂ type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR₂ = 0.0218, 398 F² values, 15 variables for SrRh₂Ga₂; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr₂Ga₂, and Na₃Pt₄Ge₄ type, I$\bar{4}$ 3m, a = 777.4(2) pm, wR₂ = 0.0234, 190 F² values, 11 variables for Sr₃Ir₄Ga₄. The gallides SrRh₂Ga₂ and Sr₃Ir₄Ga₄ exhibit complex, covalently bonded three‐dimensional [Rh₂Ga₂] and [Ir₄Ga₄] networks with short Rh–Ga (241–246 pm) and Ir–Ga (243–259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh₂Ga₂ and by 4 Ir + 8 Ga in Sr₃Ir₄Ga₄. The structure of SrRh₂Ga₂ is discussed along with the monoclinic distortion variants HoNi₂B₂ and BaPt₂Ga₂ on the basis of a group‐subgroup scheme.     

Electronic structure of GaN nanotubes

Nanotube properties are strongly dependent on their structures. In this study, gallium nitride nanotubes (GaNNTs) are analyzed in armchair and zigzag conformations. The wurtzite GaN (0001) surface is used to model the nanotubes. Geometry optimization is performed at the PM7 semiempirical level, and subsequent single-point energy calculations are carried out via Hartree–Fock and B3LYP methods, using the 6-311G basis set. Semiempirical and ab initio methods are used to obtain strain energy, charge distribution, dipole moment, |HOMO-LUMO| gap energy, density of states and orbital contribution. The gap energy of the armchair structure is 3.82 eV, whereas that of the zigzag structure is 3.92 eV, in agreement with experimental data.     

Synthesis and characterization of the unusual cluster [Ni2(GaAr′)2(η:η-μ2-C2H4)]: Ready addition of ethylene to Ni(COD)(GaAr′)2 at 25 °C and 1 atmosphere

The nickel (0) compound Ni(COD)(GaAr′)₂ (Ar′ = C₆H₃-2,6-(C₆H₃-2,6-i-Pr₂)₂), 1, was synthesized by the reaction of Ni(COD)₂ (COD = 1,5-cyclooctadiene) with (GaAr′)₂. Compound 1 reacted with ethylene at 25 °C and at 1 atm pressure to give the bimetallic cluster [Ni₂(GaAr′)₂(η¹:η¹-μ₂-C₂H₄)], 2, through the incorporation of one molecule of ethylene and displacement of COD. The structure of 2 featured an unusual Ni₂Ga₂C₂ core bicyclic structure in which the C₂H₄ moiety bridges the Ga···Ga edge of a Ga₂Ni₂ tetrahedron. The galliums each carry an η¹-bonded Ar′ substituent which complexes the nickel atom by an η⁶-π interaction with one of its flanking Ar’ rings.     

含镍WP/MCM-41催化剂二苯并噻吩加氢脱硫性能

以MCM-41为载体,以镍（Ni）为助剂,制备了Ni含量不同的WP/MCM-41催化剂。采用XRD、BET、SEM和XPS对催化剂进行了表征;以二苯并噻吩（DBT）为模型化合物,通过高压微反装置考察催化剂的加氢脱硫（HDS）活性。结果表明,Ni的加入促进了活性组分WP的生长并使其晶相尺寸略有增加,一定含量的Ni有利于提高催化剂的比表面积。Ni对WP/MCM-41催化剂二苯并噻吩HDS反应具有促进作用。少量Ni的加入有利于WP活性相的生成并增加了活性位的数量;加入过量的Ni,在催化剂中形成了具有一定活性的类似Ni-W-P结构的物种,减少了活性组分WP所占的比例,从而使催化剂DBT的 HDS活性降低。其中,Ni的质量分数为1%的催化剂（cat-Ni-1）具有相对较高活性,其DBT 脱硫率和转化率分别为76.78%和72.16%,比不加Ni的催化剂分别提高了30.04%和21.62%。二苯并噻吩在WP/MCM-41催化剂上以加氢脱硫途径为主,Ni的加入对提高加氢脱硫途径选择性起到了促进作用,且加氢脱硫选择性随Ni含量的增加而提高。     

Searching for gallium bioactive compounds: Gallium(III) complexes of tridentate salicylaldehyde semicarbazone derivatives

In the search for gallium bioactive compounds five Ga(III) complexes, [Ga^III(L-H)₂](NO₃), with tridentate salicylaldehyde semicarbazone derivatives as ligands (L) have been synthesized and characterized in the solid state and in solution by different techniques. The crystal structure of [Ga^III(L4-H)₂](NO₃)·2H₂O, where L4 is 3-ethoxysalicylaldehyde semicarbazone, was solved by X-ray diffraction methods. The gallium(III) ion is in a distorted octahedral environment, coordinated to two nearly planar and mutually perpendicular 3-ethoxysalicylaldehyde semicarbazonato anions acting as tridentate ligands through their phenol and carbonyl oxygen atoms and their azomethine nitrogen atom. Their biological potential has been explored by evaluating their activity on Mycobacterium tuberculosis, causative agent of tuberculosis, and their cytotoxicity on tumor cell lines. Three different human tumor cell lines were selected that show different degrees of resistance to metallodrugs: ovarian A2780 (low resistance), breast MCF7 (medium resistance) and prostate PC3 (high resistance) cells. Although the complexes have not shown activity on M. tuberculosis, complexation with gallium has led to the enhancement of the cytotoxic potencies of the organic compounds. Those complexes that contain a bromide substituent at the phenolate ring have shown the highest cytotoxicities. In particular, [Ga^III(L2-H)₂](NO₃), where L2 is 5-bromosalicylaldehyde semicarbazone,·has shown a remarkable cytotoxicity on A2780 tumor cell line with an IC₅₀ value of the same order than cisplatin (IC_{50 Ga-L2} = 2.4 ± 0.3 μM; IC_{50 cisplatin} = 2.0 ± 0.1 μM, 72 h incubation at 37 °C). Interestingly, this complex has also shown moderate cytotoxicity against MCF7 and PC3 cells (IC_{50 MCF7} = 30 ± 6; IC_{50 PC3} = 18 ± 3 μM). Therefore, this gallium compound could be considered a promising wide spectrum potential anti-tumor agent.     

Synthesis of Ni2P promoted trimetallic NiMoW/γ-Al2O3 catalysts for diesel oil hydrotreatment

The Ni2P promoted and γ-Al2O3 supported NiMoW sulfide catalyst consisting of 4 wt% Mo, 22 wt% W, 2 wt% Ni and 2.5 wt% Ni2P was synthesized by a co-impregnation method. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, NH3 temperature-programmed desorption (NH3-TPD) and transmission electron microscopy (TEM). The results showed that Ni2P, Ni, Mo and W species were highly dispersed over γ-Al2O3. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) showed that the presence of Ni2P brought a strong promotional effect on the HDS activity, which was further confirmed by the HDS and hydrodenitrogenation (HDN) of diesel oil under industrial conditions. The enhancement in HDN activity and stability by Ni2P addition could be attributed more to the effect of new active sites of Ni2P than that of acidity modification. The as-prepared Ni2P-NiMoW/γ-Al2O3 catalyst showed better hydrotreating performance than NiMoW/γ-Al2O3 and commercial catalysts.     

Surface site dependence to negative ion formation

The processes of electron transfer and dissociative scattering are explored for collisions of hyperthermal NO⁺ on GaAs(110). The experiments reveal a marked angular dependence to O⁻ emergence. A strong correlation between the O⁻ scattering angle and the final atom-surface interaction site provides a map of the lateral dependence to reactivity. The results are modeled by sequential neutralization, dissociation, and electron attachment steps. Classical trajectory calculations, in conjunction with an empirical opacity function, accurately reproduce the experimental results. The opacity function is interpreted as the probability that an electron will attach to a departing O fragment as a function of the last surface site the atom impacts. The experiments indicate that O⁻ emergence occurs predominantly for oxygen atoms which come in close contact with the localized dangling bond states of GaAs(110).     

Forty years of Umpolung in organometallic chemistry: from carbanionic nucleophiles to metallic electrophiles

The evolution of mechanistic insight into the nature of organometallic reactions over the last forty years is recounted from the personal perspective of a chemist trained in the empirical tradition of organometallic chemistry. Starting from the viewpoint prevailing in the 1950s of organometallics as potential carbanionic nucleophiles, this investigator has become persuaded by his researches with Group 13 organometallics of the merits of treating these reagents as organometallic electrophiles. The profound effects that a tricoordinate boron center can exert on the structure and reactivity of boracyclopolyenes is a telling illustration of such boron electrophilicity operating in an intramolecular fashion. The elucidation of the mechanisms of both the carbalumination and the hydroalumination of olefins and acetylenes has adduced cogent evidence for the rate-determining step being the electrophilic attack of tricoordinate aluminum on the carbon-carbon π-electron cloud of the substrate. Finally, in an investigation of the molecular basis for Ziegler-Natta catalysis, the Breslow-Natta soluble catalyst for the polymerization of ethylene, Cp₂TiCl₂-R_nAlCl_3−n, was examined in detail and compelling evidence has been adduced that the active catalyst site is the solvent-separated ion-pair, [Cp₂TiR]⁺ [R_nAlCl_4−n]⁻.. Here again, the polymerization reaction is initiated by an organometallic electrophile, indeed by an even more powerful cationic electrophile. The net effect of these studies has been an Umpolung in the manner with which this chemist and many of his colleagues view organometallic reaction mechanisms.     

Gallium and oxygen accumulations on gallium nitride surfaces following argon ion milling in ultra-high vacuum conditions

Metallic gallium was observed on the surfaces of GaN commercial samples following argon ion milling. SIMS measurements confirmed that the commercial GaN had approximately 0.02% bulk oxygen present. The SIMS signal was standardized using a specimen of known oxygen content, as determined by elastic recoil detection analysis using 200 MeV heavy ions of ¹⁹⁷Au. Despite this 2–5% oxygen was observed by XPS in the bulk of the GaN after the argon ion milling. This oxygen is believed to be from the original surface oxide that re-cycles on the GaN surface during the ion milling.