Polynuclear manganese grids and clusters—A magnetic perspective

High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn₄ to Mn₉. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems.     

Fluorous Synthesis of Biaryl-Substituted Proline Analogs by 1,3-Dipolar Cycloaddition and Suzuki Coupling Reactions

A solution-phase synthesis of bicyclic prolines containing four points of diversity has been developed by a two-step synthesis involving 1,3-dipolar cycloaddition of perfluoroalkylsulfonyl-protected hydroxybenzaldehydes followed by Pd-catalyzed Suzuki coupling reaction of fluorous sulfonates with boronic acids. Both reactions are conducted under microwave irradiation and reaction mixtures are purified by solid-phase extractions without performing chromatography.     

STUDY ON OXID TIVE COUPLING OF METHANE Ⅱ.CATALY TIC PERFORMANCE AND CHARACTERIZATION OF TiO_2-BASED CATALYSTS

The catalytic performance of Mn/TiO_2,La-Mn/TiO_2,Li-La-Mn/TiO_2 etc for the oxidetive coupling of methane(OCM)was investignted.Thecatalysta were cheracterised with X-ray diffraction(XRD)and X-rayphotoelectron spectroscopy(XPS).The results reveal that catalyst Li-La-Mn/TiO_2 exhibits high activity and C_2 selectivity;Ti in this catalyst exists asTi~( 4) state;Li can promote the formation of lanthanum tituate via theinteraction between La and TiO_2;the formed La_2Ti_2O_7 and La_4Ti_9O_(24) aredistributed in the inner surface layer and Mn exists in outer surface layer in lowvalence states.The high activity and C_2 selectivity of catalyst Li-La-Mn/TiO_2are intimately related to the valence states of Mn,Li,La and theirdistribution on the catulyst surface layer.     

Oxidative coupling of malononitrile with formation of 1,1,2,3,3-pentacyanopropene salts

A simple and convenient route for the synthesis of 1,1,2,3,3-pentacyanopropene salts is reported. These salts are formed by interaction of malononitrile with SeO₂ in presence of organic N-containing bases or pyridinium salts.     

A practical synthetic route to 4′-alkylaristeromycin derivatives: 4′-methylaristeromycin

(−)-(1S,4R)-4-Hydroxy-2-cyclopenten-1-yl acetate provided a convenient entry point for a 16-step chiral preparation of 4′-methylaristeromycin. This procedure is adaptable to a number of carbocyclic nucleosides with a diversity of substitution at C-4′ and C-5′ and a variety of heterocyclic bases.     

STUDIES OF MULTICOMPONENT COMPLEX OXIDE CATALYSTS FOR OXIDATIVE COUPLING OF METHANE VI.SURFACE BASICITY AND SURFACE ACTIVE OXYGEN SPECIES OF LiTi_xLa_(1-x)O_2 λ MULTICOMPONENT OXIDE CATALYSTS

The surface basicity of Ti-La-Li multicoinponent oxides has been investigated by means of CO2-TPD. The experiment results show that C2 (C2H6 C2H4) selectivity is related to surface basic strength. The surface active oxygen species have also been characterized by means of XPS, O2-TPD and so on. It has been indicated that C2 selectivity and CH4 conversion are correlated with lattice oxygen and the adsorbed oxygen on the surface of the catalyst respectively In the O2-TPD experiments, it has also been found that there are three kinds of oxygen species on the surface of the series catalvsts, which are a (100℃ 750℃) Among them α-oxvgen causes deep oxidation whileβand γ oxygen species are related to oxidalive coupling of methane (OCM).     

The Formation of C?C Bonds with the Aid of α-Halogeno Ethers,Sulfides, and Amines

α-Halogeno ethers, sulfides, and amines are reactive compounds which can be used for the formation of new C? C bonds, either as nucleophilic or as electrophilic reagents, or by α-elimination. The use of these compounds in the synthesis of many classes of organic compounds is reviewed.     

Enantioselectivity of 6-O-alkyldimethylsilyl-2,3-di-O-methyl-β-cyclodextrins as chiral stationary phases in capillary GC

Summary Clenbuterol has been determined in urine by solidphase extraction on a C₁₈ cartridge, diazotization of the eluate with nitrite, coupling of the diazonium ion with 1-(naphthyl)ethylenediamine, and separation of the azo dye formed by HPLC with a C₁₈ column and a micellar mobile phase containing 0.1 M sodium dodecyl sulphate, 12%n-butanol and 0.05 M citrate buffer, pH 3. Recoveries higher than 90% were obtained by mixing the samples with a 20% 0.2 M NaOH before extraction. Limits of detection of 51 and 6.7 ng L⁻¹ were obtained with spectrophotometric and thermal lens spectrometric detection, respectively; respective repeatabilities were 3.1% (5 μg mL⁻¹) and 5.6% (0.16 μg mL⁻¹).     

Nioboxidfluoride mit Blockstrukturen — Elektronenmikroskopische Durchstrahlungsaufnahmen und ihre Simulation

Niobiumoxidefluorides Nb₅₉O₁₄₇F, Nb₃₁O₇₇F, Nb₆₅O₁₆₁F₃ and Nb₃₄O₈₄F₂ were prepared by reaction of Nb₂O₅ and Nb₃O₇F at 1 270°C. These niobiumoxidefluorides have blockstructures which were examined by high resolution electron microscopy. The observed images of the crystal structures were compared with computer simulated images.

     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.