Electron in liquid ammonia

In most cases, the reaction requires external stimulation in which a catalytic amount of electrons is injected into the solution. Solvated electrons in liquid ammonia, sodium amalgam in the same solvent71 light,66-68 electrodes1167 and... 

It was also observed, in 1973, that the fast reduction of Cu ions by solvated electrons in liquid ammonia did not yield the metal and that, instead, molecular hydrogen was evolved [11]. These results were explained by assigning to the quasi-atomic state of the nascent metal, specific thermodynamical properties distinct from those of the bulk metal, which is stable under the same conditions. This concept implied that, as soon as formed, atoms and small clusters of a metal, even a noble metal, may exhibit much stronger reducing properties than the bulk metal, and may be spontaneously corroded by the solvent with simultaneous hydrogen evolution. It also implied that for a given metal the thermodynamics depended on the particle nuclearity (number of atoms reduced per particle), and it therefore provided a rationalized interpretation of other previous data [7,9,10]. Furthermore, experiments on the photoionization of silver atoms in solution demonstrated that their ionization potential was much lower than that of the bulk metal [12]. Moreover, it was shown that the redox potential of isolated silver atoms in water must... 

Simple cavity models have been used to study solvated electrons in liquid ammonia. In that case the dominant interactions arise from long range polarization effects, so that the energy of the localized state is not very sensitive to the fluid deformation in the vicinity of the localized charge. In the case of an excess electron in liquid helium, however, the electron-fluid interaction arises mainly from short range electron-atom interactions, and we shall show that the localized excess electron in a cavity in liquid helium lies lower in energy than the quasi-free electron. 

Absorption Spectrum of e aq. The absorption spectrum of the hydrated electron is shown in Figure 1. The evidence that this spectrum is that of eaq is at least four-fold. First, the spectrum is suppressed by known electron scavengers, such as H30+, 02, N20 (4, 18). Second, it resembles in form the absorption bands of the solvated electron in liquid ammonia and methylamine (4, 18). Third, the rate constants calculated from the decay of this absorption in the presence of scavengers... 

More recently still the electron produced in this and in other ways has been shown to have a finite independent existence as a hydrated species136. This is very similar to solvated electrons in liquid ammonia known since the early work of Franklin and Kraus137. The solvated electron in liquid ammonia disappears very slowly in the absence of a catalyst, but the life of the hydrated electron is much shorter if they undergo no other reactions, they are removed as follows... 

Thompson, J. C., "Electrons in Liquid Ammonia. Oxford Univ. Press (Clarendon), London and New York, 1976. 

I enjoyed my research in Utah, from 1986 to 1990, at Brigham Young University, Provo, collaborating with Professor Reed Izatt and Professor Noel L. Owen, where calorimetric and electrometric studies were applied for used and fresh engine oils and FTIR spectrometric studies of solvated electrons in liquid ammonia with wood surface and wood components were analyzed. 

Thompson JC (1976) Electrons in Liquid Ammonia. Clarendon Press, Oxford... 

The chemistry of gold is more diversified than that of silver. Six oxidation states, from -I to III and V, occur in its chemistry. Gold(-I) and Auv have no counterparts in the chemistry of silver. Solvated electrons in liquid ammonia can reduce gold to give the Au" ion which is stable in liquid ammonia (E° = -2.15 V). In the series of binary compounds MAu (M = Na, K, Rb, Cs), the metallic character decreases from Na to Cs. CsAu is a semiconductor with the CsCl structure and is best described as an ionic compound, Cs+Au . The electron affinity of gold (—222.7 kJ mol"1) is comparable to that of iodine (-295.3 kJ mol-1). Gold in the oxidation state -I is also found in the oxides (M+ Au O2 (M = Rb, Cs) these, too, have semiconducting properties.1... 

Golden S, Tuttle TR, M, LS. (1987) Effect of added salt on the optical absorption spectra of solvated electrons in liquid ammonia. J Phys Chem 91 1360-1365. 

The solvated electron in liquid ammonia was discovered in 1864 by Weyl, and was identified in 1908 by Kraus as an electron, e am, in a cavity surrounded by ammonia molecules. It is prepared when an alkali metal, for example sodium, is dissolved in ammonia, to form a stable blue color under these conditions the electron is present in equilibrium with the metal atom and cation [34]. By contrast, e am produced by pulse radiolysis of liquid ammonia is unstable due to its reactions with other radiolysis products for example, in pure ammonia at —45 °C, its lifetime is ca. 7 ps [35], The major decay reactions are thought to involve the oxidizing radicals NH2 and NH [36], because addition of potassium ethoxide stabilizes e am this is explicable, since ethoxide ion is expected to scavenge these radicals [36a]. 

Hoijtink et al. [27] also developed an alternative method of generating anionic species, which was improved by Szwarc et al. [28]. The technique involves potentiometric titration of aromatic compounds with a standard solution of Na-biphenylide. The extremely negative reduction potential of biphenyl assures that most of the common aromatics can be reduced to at least their respective radical anions. The values of the thermodynamic reduction potentials are generally obtained from the potentiometric titration curve. As all experiments are usually carried out in ethereal solutions, such as tetrahydrofuran (THF) or dimethoxyethane, problems of follow-up processes are less severe. Later, Gross and Schindewolf [29] reported on the potentiometric titration of aromatics using solvated electrons in liquid ammonia. 

Vast material on the properties of solvated electrons in liquid ammonia has been accumulated by now . i23-i27> Ammonia was the first solvent for which it was shown that the properties of solvated electrons obtained by different methods (by dissolving alkali metals, by pulse radiolysis, and by cathodic generation) were identical (see Fig. 4). 

Fig. 4. Spectra of optical absorption of solvated electrons in liquid ammonia at —65-70 °C ...

Fig. 6. Equilibrium potential of electron electrode versus logarithm of total concentration of electrons in liquid ammonia against a background of (O)O.IS M Nal and ) 0.5 M KI dotted lines theoretical slopes at n = 1 and n = 2 temperature 40 °C reference electrode Pb/Pb (0.05 mol/1) (158)...

By the beginning of 7O s only one work on the kinetics of electrochemical generation of solvated electrons was known Later, however, a number of papers reflecting the increased interest in this problem appeared. A brief annotation of the works pertaining to the cathodic generation of solvated electrons in liquid ammonia and methylamine and also in hexamethylphosphotriamide is given in Table 7. 

Jortner [85] obtained the heat of solution of the electron in liquid ammonia using the following Bom—Haber cycle. 

Thermodynamic functions for the electron in liquid ammonia (relative to H" ) have been calculated by Jolly [86]. The free energy and heat of formation at 298°K are 46.0 and 37.5 kcal mole , respectively. The entropy of formation is —13.0 cal °K mole". It is possible to calculate that the equilibrium constant for the reaction... 

This is a fascinating approach to the study of solvated electrons and has been extended by Dewald and Tsina (27) to the reaction of water with the electron in liquid ammonia. For the mixture water-Na-liquid NH3 these authors find a very slow reaction and conclude that k17 < 5 X 10"3M 1 sec."1 at -34°C. 

Of greater interest to the coordination chemist is the observation that solvated electrons in liquid ammonia can reduce gold to Au, characterized by an absorption band at 278 nm ( = Sx 10 ). Electrochemical studies show that Au is stable in liquid ammonia and the anodic wave in the cyclic voltammogram, corresponding to oxidation of Au to Au°, occurs at -2.15 These solutions have not been studied by coordination chemists, but they have great potential for synthesis of gold complexes in low oxidation states. Au has tte electron configuration [Xe]4/ 5d 6s and is isoelectronic with H. ... 

Thompson. J.C. Electrons in Liquid Ammonia Oxford Univ. Press Oxford. 1976. 

Excess electrons in polar solvents exhibit strong optical absorption. Especially, the hydrated electron and the solvated electron in liquid ammonia have been the subject of intensive investigations (Hart, 1965 Jortner and Kestner, 1973). 

Thompson JC (1976) Monographs on the physics and chemistry of materials electrons in liquid ammonia. Oxford University Press, London, Drake SR, Otway DJ (1991) J Chem Soc Chem Commun 1060... 

The electron-ion and electron-ammonia interactions were treated using pseudopotentials. For Li we used a bare coulomb potential truncated at a radius (Rq) that yields essentially the correct spectroscopic term value for the 2s electron. The electron-solvent molecule potential consisted of electron-charge site contributions but with Rq = 1.0 A for the protons. No allowance was made for polarization or exchange contributions. Our crude potential is justified a posteriori since it yields a reasonable description of an electron in liquid ammonia. ... 

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