Alkalides synthesis

Novel anions stabilized by alkali-polyether cations The ability of a crown (such as 18-crown-6) or a cryptand (such as 2.2.2) to shield an alkali cation by complex formation has enabled the synthesis of a range of novel compounds containing an alkali metal cation coordinated to a crown or cryptand for which the anion is either a negatively charged alkali metal ion or a single electron (Dye Ellaboudy, 1984 Dye, 1984). Such unusual compounds are called alkalides and electrides , respectively. 

Role of Cation Complexants in the Synthesis of Alkalides and Electrides... 

Tsai, K.-L. and Dye, J.L., Synthesis, properties, and characterization of nanometer-size metal particles by homogeneous reduction with alkalides and electrides in aprotic solvents, Chem. Mater., 5, 540,1993. 

Interestingly, a considerable number of trapped electrons are present in most alkalides. However, their concentration (up to several percent) can be significantly reduced by applying an excess of metal during the synthesis. Na ... 

The chemistry of the alkali metals has in the past attracted little attention as the metals have a fairly restricted coordination chemistry. However, interesting and systematic study has blossomed over the past 25 years, largely prompted by two major developments the growing importance of lithium in organic synthesis and materials science, and the exploitation of macrocyclic ligands in the formation of complexed cations. Section 12.4 deals with the use of complexed cations in the generation of alkalides and electrides. 

Synthesis of Alkalides and Electrides James L. Dye, Mikhail Y. Redko,... 

Among the intriguing developments in alkalide chemistry has been the recent synthesis of inverse sodium hydride, which contains a sodide ion, Na, and an ion encapsulated in 3 adamanzane. The H" in this structure is strongly coordinated by four nitrogen atoms in the adamanzane ligand, shown in Figure 8-8(b). 

The major concern in the preparation and study of alkalides and electrides is their extreme sensitivity to air, moisture, and especially elevated temperatures. Thus, ordinary glove box procedures do not suffice without provision to keep the samples cold (below about — 40°C) at all times during and after synthesis. It should be noted. 

The next question to be asked concerns the composition of the particles. For the case of monometallic particles this could in principal be a trivial question. If the particle is known to contain a single element, the only question which then arises concerns the oxidation states of the metal, and this can be determined by X-ray photoelectron spectroscopy. For example, the colloidal metals described in Section 6.2.2.1 and prepared by Dye and coworkers by alkalide and electride reduction of salts of gold, copper, platinum, nickel, and molybdenum (as well as several main group metals and metalloids) were analyzed by XPS [73] which showed the presence of only zerovalent metal. Oxidized metal was detected only for nickel and molybdenum (among the transition metals) and this only after exposure to an oxidizing solvent such as methanol. These results show that if a sufficiently powerful reducing agent is used in the colloid synthesis, the surface of the particles can be kept in a reduced metallic state. 

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