Cocondensation, compounds produced

The stability of molecules depends in the first place on limiting conditions. Small, mostly triatomic silylenes and germylenes have been synthesized successfully at high temperatures and low pressures, 718). Their reactions can be studied by warming up the frozen cocondensates with an appropriate reactant, whereas their structures are determined by matrix techniques 17,18). In addition, reactions in the gas phase or electron diffraction are valuable tools for elucidating the structures and properties of these compounds. In synthetic chemistry, adequate precursors are often used to produce intermediates which spontaneously react with trapping reagents 7). The analysis of the products is then utilized to define more accurately the structure of the intermediate. 

A number of unstable and transient species have been synthesized via matrix cocondensation reactions, and their structure and bonding have been studied by vibrational spectroscopy. The principle of the method is to cocondense two solute vapors (atom, salt, or molecule) diluted by an inert gas on an IR window (IR spectroscopy) or a metal plate (Raman spectroscopy) that is cooled to low temperature by a cryocooler. Solid compounds can be vaporized by conventional heating (Knudsen cell), laser ablation, or other techniques, and mixed with inert gases at proper ratios [128]. In general, the spectra of the cocondensation products thus obtained exhibit many peaks as a result of the mixed species produced. In order to make band assignments, the effects of changing the temperature, concentration (dilution ratios), and isotope substitution on the spectra must be studied. In some cases, theoretical calculations (Sec. 1.24) must be carried out to determine the structure and to make band assignments. Vibrational frequencies of many molecules and ions obtained by matrix cocondensation reactions are listed in Chapter 2. 

Little is yet known of cage polysilanes, although many such structures should be possible. In the permethyl series when Me2SiCl2 and MeSiClj are cocondensed with Na-K alloy in THF in the presence of naphthalene, six different polycyclic compounds are produced, all in small yield, along with (Me2Si)g and polymer ... 

Metal-containing polymers can be synthesized by the vapor deposition polymerization of various monomer systems including organometallic compounds and metal-monomer co-condensates. Such co-condensates are produced by simultaneous or layer-by-layer deposition of metal and monomer vapors on substrate plates at low temperatures (usually, 77 K). Polymerization can proceed in different ways. Some metal-monomer systems polymerize during cocondensation (Ge and Sn with acetylene [11], Mg with CN-substituted p-xylylene [12]), most probably due to heat released at condensation. In references 13-16, co-condensates of metals (Pd, Ag, Au, etc.) and vinyl monomers... 

Thus the cocondensation of La, Nd, Sm or Er with butadiene or 2,3-dimethylbutadiene at TTK produces brown solids which can be extracted by toluene or THF yielding paramagnetic ill-defined compounds for which the formulas A, B or C are discussed (21 ) ... 

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