Direct synthesis stoichiometry

Direct synthesis of NF3 from nitrogen and fluorine was not effected until 1964, when Maya obtained yields up to 30% on passing an N2-F2 mixture at a pressure of 20- 40 mm through an electric discharge in a tube cooled to — 196°C (207). This method is similar to that used in the synthesis of oxygen fluorides from the elements (144,259), except that in the latter case different oxygen fluorides are produced by changing the stoichiometry of the mixture of reactants, whereas with N2-F2 mixtures only NF3 results. 

These are quite important compounds. A number of stoichiometries exist, the most important being Ln2S3. These can be made by direct synthesis, heating the elements together, or by passing H2S over heated LnClg. EU2S3 cannot be prepared by this latter route. 

Carbides are likewise formed in a number of stoichiometries. LnC2 are the most important they can be made by direct synthesis from the elements as well as by heating the oxide or hydride with carbon. They have the CaC2 structure with short C-C distances (around 1.28 A) but have metallic conductivity and thus may be formulated Ln + (C2 ) (e ). C2 units are also found in Ln2C3 (PU2C3 structure), while LnC, Ln2C, and LnsC are also known. The carbides are readily hydrolyzed, affording a mixture of hydrocarbons whose composition depends on temperature. 

Thiopicolinamides are known to form chelates with metal ions. The synthesis of suitable bis(thiopicolinamides) to serve as ligands for polymer formation was reported in 1958 (2-4, 20). Heating a metal acetylacetonate with a stoichiometrie amount of a bis(thiopicolinamide) effects chelate exchange and the formation of polymer as a residue product (VIII-1). Acetylacetone is removed as a volatile by-product. Direct synthesis of these polymers from a metal acetate and the bis(thiopicolinamide) has been used more widely. Generally, methanolic solutions of the metal acetate are added to solutions of the bis(ligand) in dimethylformamide, benzene, or chloroform (8, 20, 26,31, 32). Almost always the polymer precipitates in quantitative yield, but in some cases, other isolation techniques have been required. 

A number of synthetic procedures are available (Ai2). (2) For precisely defined stoichiometries, the isobaric, two-bulb method of Herold is preferred H5, H6, H2). (2) To generate compounds suitable for organic synthesis work, graphite and alkali metal may be directly combined, and heated under inert gas (Pl, lA). (5) Electrolysis of fused melts has been reported to be effective iN2). 4) Although alkali metal -amine solutions will react with graphite, solvent molecules co-inter-calate with the alkali metal. Utilization of alkali metal-aromatic radical anion solutions suffers the same problem. 

Cyanocuprates constitute a class of organocopper compounds that finds applications in organic synthesis.234 They are prepared by the direct reaction of an organolithium reagent and CuCN, with two different types of compounds being prepared depending on the stoichiometry employed the 1 1 ratio leads to RCu(CN)Li compounds whereas the 2 1 mixture affords R2Gu(GN)Li2. The lower- order or 1 1 cyanocuprates usually display the Cu-C-N-Li... 

It is quite often possible to prepare hydroxypyridinone complexes directly by one-pot synthesis from the appropriate hydroxypyranone, amine, and metal salt 90-92). They can also be prepared by reacting complexes such as P-diketonates with hydroxypyridinones (see e.g., Ce, Mo later). Several maltolate complexes, of stoichiometry ML2, ML3, ML4, or MOL2, have been prepared by electrochemical oxidation of the appropriate metal anode, M — a first-row d-block metal (Ti, V, Cr, Mn, Fe, Co, Ni), In, Zr, or Hf, in a solution of maltol in organic solvent mixtures 92). Preparations of, e.g., manganese(III), vanadium(III), or vanadium(V) complexes generally involve oxidation... 

The standard approach to the synthesis of oxides in polycrystalline form is the direct reaction of a mixture of metal oxide starting materials at high temperature. The ratios of the starting materials will control the stoichiometry of the product provided the volatilities of the starting materials are relatively low. Syntheses of oxides containing volatile components are discussed in greater detail in the following sections. 

The direct electrochemical synthesis (Scheme 2) of the addncts of organomagnesinm halides with 2,2 -bipyridine (6) and salts of organodihalogenomagnesinm(II) anions (7) was reported by Hayes and coworkers . Adducts of different stoichiometry and 7 were obtained in the electrochemical oxidation of magnesium in ACN solutions containing organic halides RX (8), a.ro-dihalides XR X (9) and 8 with ammonium salts R NX, respectively. All new products showed none of the typical reactions of Grignard reagents. 

This supramolecular directing concept has led to a family of materials whose structure, composition, and pore size can be tailored during synthesis by variation of the reactant stoichiometry, nature of the surfactant molecule, or by postsynthesis functionalization techniques [113]. 

The only other crystallographic result reported for a berkelium chal-cogenide besides those summarized in Table II is a cubic lattice parameter of 0.844 nm for Bk2S3 (155). The microscale synthesis of the brownish-black sesquisulfide was carried out by treatment of berkelium oxide at 1400 K with a mixture of H2S and CS2 vapors. In later work (136,137), the higher chalcogenides were prepared on the 20- to 30-jug scale in quartz capillaries by direct combination of the elements. These were then thermally decomposed in situ to yield the lower chalcogenides. The stoichiometries of these compounds have not been determined directly. 

Several high-temperature procedures have been described in the literature for the preparation of the transition-metal dioxides. Direct oxidation of the metals, lower oxides, chlorides, or nitrate precursors provides a convenient route to the dioxides of several metals Ti, Mn, Ru, Rh, Os, Ir, and Pt.1,3-5 (Syntheses of the rutile forms of rhodium and platinum dioxides by direct oxidation requires application of high pressures.5) Reduction of higher oxides is the most common method of synthesis for these dioxides V02, Nb02, Mo02, W02, and /3-Re02.4,6-8 Stoichiometry in these reactions is most readily controlled by use of the respective metal or a lower oxide as reductant. Chromium dioxide is normally synthesized by hydrothermal reduction of the trioxide.9... 

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