Condensation of metal vapor

Condensation of metal vapors followed by deposition on cooler surfaces yields metal powders as does decomposition of metal hydrides. Vacuum treatment of metal hydrides gives powders of fine particle size. Reaction of a metal haHde and molten magnesium, known as the KroU process, is used for titanium and zirconium. This results in a sponge-like product. 

Figure 1. Condensation of solvent vapor (A) and co-condensation of metal vapor with solvent vapor (B).

The simplest case of M-M bonds was observed in Mj+ dimers without surrounding coordinate ligands. These compounds (with n = 0) were synthesized for a number of metals by fast condensation of metal vapors in inert-gas matrices at low temperatures [130-135]. 

Direct condensation of metal vapors with trifluorophosphine at -196°C provides a convenient alternative to the high-pressure route to metal-PF3 complexes. The reactions of Mo, Cr, Co, Ni, and Pd vapors with PF3 yield only one volatile product in each case, namely Mo(PF3)6 (132), Cr(PF3)6, Co2(PF3)g, Ni(PF3)4, and Pd(PF3)4 (128), respectively. The yields are good, 40-100% depending on the metal vapor used. Some defluorination of the PF3 accompanies the formation of Cr(PF3)6. No complex could be isolated from the manganese vapor-PF3 reaction, although some defluorination seems to have occurred. The reaction of iron and PF3 is complex,... 

Introduction Reactions in the Films Obtained by Co-Condensation of Metal Vapor with Organic Compounds. 697... 

Reaction of cyclopentadiene directly with metal chips under reflux or in liquid ammonia has been used in the preparation of the M(C5H5)291-92 and Ca(C5H4Me)2(DME)93 compounds, respectively. However, a more general reaction method is co-condensation of metal vapor, the vapor of the cyclopentadiene of choice, and the solvent, which is typically hexane or toluene, according to Eq. (1 1).88-89,94... 

Condensation of metal vapors at low temperatures with CO allows the preparation or spectroscopic identification (matrix isolation technique) of several carbonylic species , e.g., Fe(CO)5, Ta(CO)s, etc., including the unstable carbonyls of the inner transition metals . Yields are low. 

The ligand source is simply a nozzle or other vapor dispersion device to introduce volatile co-reactants or gases into the vacuum system and thence to the co-condensation site co-condensation of metal vapors with solutions of involatile substrates requires special techniques, which will be discussed in Section 1.08.6. 

Figure 15 Condensation of metal vapors into solutions.

Figure 20 shows commercial, rotating MVS machines equipped with twin electron-beam furnaces, suitable for both co-condensation reactions and condensation of metal vapors into solutions (Section 1.08.6.2). 

A very important method of preparation of diene compounds is the condensation reaction of dienes with metal vapors. The reaction is carried out at low temperature and at low pressure in a specifically designed flask containing the diene either neat or in solution. The metal atoms vaporize from the electrically heated metal wire and react with dienes which are present in the liquid phase(Figure 8.7). Often, such condensations of metal vapors with dienes are carried out in matrices at liquid nitrogen temperature. In this manner, the air-stable compounds [M(C4H6)3] (M = Mo, as... 

Condensation of metal vapors with various 6e ligands (cf. preparation of diene complexes, Chapter 8) allows the synthesis of many complexes which would be difficult or impossible to obtain by other methods owing to the reactivity of substituents. The following bisarene complexes were obtained in this manner [Cr(arene)2], where arene = PhX (X = F, Cl, CF3, COOMe, Me, /-Pr) or (X = F, Cl, CF3,... 

The condensation of metal vapors with hexafluorobenzene and benzene gives unstable arene complexes of V, Cr, Mn, Fe, Co, Ni, and Pd, for instance, [Cr(C6H6)(C5F6)]. The condensation of vapors of chromium or iron with the mixture of vapors of benzene and PF3 or hexafluorobenzene and PF3 leads to the formation, with low yields, of the derivatives [Cr(C6F6)(PF3)3], [Cr(PhH)(PF3)3], and [Fe(PhH)(PF3)2]. Heteroleptic compounds of chromium, for example, [ (CgF ) (Pp3)3], are stable in contrast to [Cr(C6F6)2] which is unstable and explosive. The condensation method was also utilized for the preparation of hexahapto pyridine complexes of chromium. 

Conventional magnetic metal powders, with a microscopic grain size, are usually obtained by mechanical attrition, atomization, condensation of metal vapor, electrol3dic decomposition from solution, reduction of metal compounds, centrifugal atomization, decomposition of metal hydrides, etc. Hyperfine metals prepared by chemical method which offers the following principal advantageous [35] ... 

With the exception of direct condensation of metal vapors in micropores, the preparation of metal clusters involves at least two steps, viz., the loading of a metal precursor in the microporous material and the decomposition or reduction of the precursor yielding metal clusters. These two steps are highly interdependent and the second is often crucial for governing the final metal dispersion. The different strategies of metal cluster preparation will be examined in this section, and detailed examples of preparations for specific zeolites and metals will be given in Sect. 3. 

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