Carbometallate: Komplexe Anionenverbände [MoC4/26—] in der Kristallstruktur von Pr[MoIIC2]

Carbometalates: Complex Anions equation/tex2gif-stack-4.gif [MoC_4/2^6—] in the Crystal Structure of Pr equation/tex2gif-stack-5.gif [Mo^IIC₂] Criteria for the existence of carbometalates are established and discussed in a broader context. The concept is then applied to the novel compound Pr₂[MoC₂], which is characterized by chemical analyses, X‐ray diffraction and metallography. The crystal structure (tetragonal, P4₂/mnm, Z = 4, a = 581.29(8) pm, c = 1032.53(14) pm) consists of layered polyanions equation/tex2gif-stack-6.gif[MoC_4/2^6—] of distorted vertex and edge sharing MoC₄ tetrahedra. Praseodymium is also in a distorted tetrahedral coordination by carbon. The physical properties show “bad metal” behaviour and localized magnetic 4f‐moments in agreement with the existence of Pr³⁺‐species. A detailed bonding analysis using both the electron localization function ELF and the COHP method justifies the interpretation of the title compound as a carbomolybdate(II).     

水中痕量钼(Ⅵ)的4-(2-吡啶偶氮)-间苯二酚螯合活性炭吸附富集分光光度法测定

提出了一种简单快速预富集水中痕量钼（Ⅵ）的新方法，方法的机理在于4－（2－吡啶偶氮）－间苯二酚（PAR）与钼（Ⅵ）螯合后被活性炭中附，然后用NaOH解吸下来，再用水杨基荧光酮与钼（Ⅵ）显色，分光光度法测定钼（Ⅵ）的含量；详细研究了影响Mo-PAR螯合物定量吸附于活性炭上的各种参数，找出了最佳吸附－解吸条件，包括吸附酸度、PAR用量、吸附时间、解吸酸度等；该法的主要优点是操作简单、快速，干扰小，避免了常规方法中用浓硝酸消化活性炭费时和污染大的解吸方法，该法已用于测定水中痕量钼（Ⅵ），加标回收率达到94％－97％。     

催化动力学极谱法测定痕量钼

在稀Ｈ２ＳＯ４介质中，钼（Ⅵ）对硫酸联氨还原乙基橙的反应有强烈的催化作用。建立了催化动力学极谱法测定痕量钼的新体系，方法线性范围为２０－３００ｎｇ／ｍＬ，检出限为３．５４ｎｇ／ｍＬ。方法应用于尿中中钼的测定，结果满意。     

Relationship between the molybdenum phases and the conversion of n-butane over Mo/HZSM-5

The conversion of n-C₄H₁₀ was undertaken on MoO₃/HZSM-5 catalyst at 773–973 K and the phases of molybdenum species were detected by XRD. The XRD results show that bulk MoO₃ on HZSM-5 can be readily reduced by n-C₄H₁₀ to MoO₂ at 773 K and MoO₂ can be gradually carburized to molybdenum carbide above 813 K. The molybdenum carbide formed from the carburization of MoO₂ with n-C₄H₁₀ below 893 K is -MoC_1−x with fcc-structure, while hcp-molybdenum carbide formed above 933 K. During the evolution of MoO₃ to MoO₂ (>773 K) or the carburization of MoO₂ to molybdenum carbide (>813 K), deep oxidation, cracking and coke deposition are serious, in particular at higher reaction temperatures, these lead to the poor selectivity to aromatics. Aromatization of n-C₄H₁₀ can proceed catalytically on both Mo₂C/HZSM-5 and MoO₂/HZSM-5, the distribution of the products for the two catalysts is similar below 813 K, but the activity for Mo₂C/HZSM-5 is much higher than that for MoO₂/HZSM-5.     

Oxidation of 2,6-di-tert-butylphenol with polymer anchored molybdenyl and vanadyl complexes

The oxidation of 2,6-di-tert-butylphenol with tert-butylhydroperoxide (Bu^tO₂H) has been studied using polymer (XAD₄) anchored salicylaldoxime, 1,3-propylene-bis-salicylaldimine and o-phenylene-bis-salicylaldimine complexes of molybdenum and vanadium in acetonitrile. The predominant products formed in the oxidation reactions were 2,6-di-tert-butylbenzoquinone (BQ) and 3,3′-5,5′-tetra-tert-butyldiphenoquinone (dPQ), whereas with some only 2,6-di-tert-butylbenzoquinone was formed. This is the first reported use of polymer anchored molybdenyl and vanadyl complexes in selective oxidation of 2,6-di-tert-butylphenol. Solvent plays an important role in this reaction. The effects of varying the ligand, metal and the support on the catalytic activity in the oxidation of 2,6-di-tert-butylphenol have been studied. With polymer anchored MoO₂(salpen), 81% of 2,6-di-tert-butylbenzoquinone was formed from 2,6-di-tert-butylphenol.     

Crystal structure of the Molybdenum(V) Diphosphate KMoP2O8 isotypic with KNbP2O8

A new molybdenum(V) diphosphate KMoP₂O₈ has been isolated. The single crystal X-ray diffraction study of this phase has shown that it is isotypic with KNbP₂O₈. It crystallizes in the P2₁/n space group a = 5.0862(4), b = 11.720(1), c = 11.486(1) Å, β = 90.91(1)°. The structure of this phase is compared with those of other molybdenum(V) diphosphates. This tunnel structure is described in terms of [MP₂O₈]₈∞ ribbons running along ā, showing close relationships with the titanophosphate NaTiP₂O₇. The existence of one free apex for each MoO₆ octahedron and each P₂O₇ group, respectively, is emphasized, allowing a great flexibility of the structure.     

用N2O-C2H2火焰原子吸收光谱法测定羰基镍粉中钼含量

运用了N2O—C2H2火焰原子吸收光谱法进行羰基镍粉钼含量的测定。介绍了钼最佳测定条件及呈良好线性范围的浓度,同时对样品消化处理条件及在测定中样品的干扰因素进行了综合考虑．该方法的相对标准偏差均小于1.0％(n=6)，回收率均在97．0％～102．0％(n=6)之间．达到了实验室分析质量控制的要求．     

Theoretical study on interaction of different coordination modes of BH4 ligand with transition metal in [TM(BH4)(CO)4] (TM = Cr, Mo)

Density functional calculations were performed on bonding and structural features of [(ηⁿ-BH₄)TM(CO)₄]⁻ (n = 1, 2, 3; TM = Cr, Mo) complexes. Calculations show that the ground state is bidentate which is in good agreement with experimental results. It has been found that the bridge and terminal hydrogen atoms will interchange by two pathways: (i) twist of BH₄ about one of the bridge B-H and (ii) twist of BH₄ about one of the terminal B-H. The molecular orbital calculations and natural bond orbital methodologies for different isomers of these complexes have been evaluated. The final results indicate that case (i) is more preferable relative to another case.     

Identification by Electron Probe Microbeam Analysis of Submicron Borides in Joints of Nickel Base Superalloys

The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM₂B₂ (M=Mo and M=Co, Cr) and the solid solution boride [Cr_1–x (Mo, W)_x]B.     

Determination of Trace Molybdenum in Biological Matrices by Neutron Activation Analysis

Based on consecutive extractions using bismuth diethyldithiocarbamate and thallium diethyldithiocarbamate as reagents, molybdenum was selectively and highly enriched from biological matrices, and then subjected to neutron activation analysis. Most of interfering elements, e.g., Na, K, Br, P, Fe, U, etc. were simultaneouly removed and the preconcentrated samples always showed only the r rays from molybdenum after neutron bombardment. Thus, molybdenum in the biological matrices could be accurately determined.