Metal-ammonia solutions stability

Deigen and Pekar (16) have shown that in the polarons the energy correction caused by the hyperfine interaction equals zero in the first approximation. Hence, the width of the polaron line determined by the hyperfine interaction also equals zero. At the same time for the local electron centers such an interaction is actually a predominant factor which determines the width of the line. This makes it possible to distinguish by way of experiments the polarons from the local electron centers. Evidently, the solvated electrons produced during irradiation of the polar liquids are the mobile polarons. At low temperatures the polarons are stabilized in the form of local electron centers (peculiar F-centers) (6, 19). Actually, in the metal-ammonia solutions the width of the EPR line of the solvated electron comprises some hundredths of oersted however, the freezing of the solution at 77 °K. results in widening of this line up to 3.4 (37) or 11 (58) oe. 

Stability. On evaporating freshly prepared metal-ammonia solutions, a residue of the metal is left indicating that there are no chemical changes in the solution. But on allowing the solution to stand for some time, the blue color gradually disappears with evolution of hydrogen according to the reaction... 

He also interpreted much of the data at low concentrations as an electrolyte solution while at high concentrations they were discussed as liquid metal. Much of the earlier studies of trapped electrons were dominated by the study of metal ammonia solutions, in part because of their exceptional stability. These studies were first collectively presented in the proceedings of Colloque Weyl I in 1963 (Lepoutre and Sienko, 1963). 

The metal and ammonium salts of dithiophosphinic acids tend to exhibit far greater stability with respect to this thermal decomposition reaction, and consequently these acids are often prepared directly in their salt form for convenience and ease of handling. Alkali-metal dithiophosphinates are accessible from the reaction of diphosphine disulfides with alkali-metal sulfides (Equation 22) or from the reaction of alkali-metal diorganophosphides with two equivalents of elemental sulfur (Equation 23). Alternatively, they can be prepared directly from the parent dithiophosphinic acid on treatment with an alkali-metal hydroxide or alkali-metal organo reagent. Reaction of secondary phosphines with elemental sulfur in dilute ammonia solution gives the dithiophosphinic acid ammonium salts (Equation 24). 

The lack of homopolyatomic anions for elements to the left of group IV In Table I is noteworthy. Zlntl reported no success with reactions of alkali metal alloys of the copper and zinc family elements and of thallium with liquid ammonia, and the generally stabilizing effect of crypt has not been evident In our own Investigations of alloys of mercury and thallium. On the other hand. It is possible to Isolate a white crypt-potassium gold compound from ammonia solutions at low temperatures which decomposes to elemental gold (+ ) above about -10°C (30). 

Osmium(viii).—From studies of the extraction of OSO4 from alkaline aqueous solutions by carbon tetrachloride, it has been suggested that the anion [0s04(0H)] may exist in these media. Similar evidence was found for the presence of [OsOjN]" in aqueous ammonia solutions of 0s04. Examination of the i.r. spectra of a series of metal complexes of the ligand 8-amino-7-hydroxy-4-methylcoumarin, including [OsO LjjClj, indicate a correlation between certain vibrational bands, e.g. v(M—N), and the stability of the compounds. ... 

In a similar manner the so-called Zintl salts composed of alkali metal cations and clusters of metals as anions (see Chapter 16) were known in liquid ammonia solution but proved to be impossible to isolate Upon removal of the solvent they reverted to alloys. Stabilization of the cations by complexation with macrocyclic ligands allowed the isolation and determination of the structures of these compounds. 

The stability of a complex ion is measured by its formation constant Kf (or stability constant), the equilibrium constant for formation of the complex ion from the hydrated metal cation. The large value of Kf for Ag(NH3)2+ means that this complex ion is quite stable, and nearly all the Ag+ ion in an aqueous ammonia solution is therefore present in the form of Ag(NH3)2+ (see Worked Example 16.12). 

Since ammonia forms stable, water-soluble complexes with many metals, leaching can be carried out under alkaline conditions to give these metals in solution. Of particular interest are the metals copper, nickel and cobalt, which form particularly stable amines lliat have been well characterized as having the following approximate stability constants (at high ionic strength) Cu, 2 = Cu , 4 = 13 Ni , 6 = 9 = 5 Fe ,j52 < 2. 

Silver may be separated from Ce, Zr, Th, Be, and Fe(III), on strongly acidic cation-exchangers, by converting these metals into anionic complexes, or separated from Cu, U, Al, and Zn by selective elution with nitric acid [14]. After retention of Pb, Ag, and Hg on Dowex 50, lead is eluted first with 0.25 M ammonium acetate, then silver with 0.5 M ammonia solution. Silver has been separated on a cation-exchanger from Hg, Co, Ni, and Zn on the basis of the differing stabilities of their EDTA complexes at pH 4.6 [15]. Silver retained in a column with a macroporous cation-exchange resin bed has been eluted with 2 M HNO3 or 0.5 M HBr in aqueous acetone solution [16]. 

A third solution is via primary reduction to the benzylic alcohol which is then stabilized as its anion during the metal-ammonia reduction [119, 217], and can be reoxidized by the Oppenauer method (Fig. 9.9). 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Can catch fire when in contact with porous materials such as wood, asbestos, cloth, soil, or rusty metals Stability During Transport Stable at ordinary temperatures, however when heated this material can decompose to nitrogen and ammonia gases. The decomposition is not generally hazardous unless it occurs in confined spaces Neutralizing Agents for Acids and Caustics Flush with water and neutralize the resulting solution with calcium hypochlorite Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

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