The Electronic Properties of Metal Solutions

Abstract

The introduction of sodium metal into anhydrous liquid ammonia produces an intensely coloured blue solution in which localised excess electrons, sodium cations, and various agglomerates of these species co-exist in equilibrium. With increasing metal concentration the system transforms into a bronze metallic conductor. In the transitional range, cooling of the (homogeneous) sample can give rise to a remarkable liquid-liquid separation in which both dilute (blue) and concentrated (bronze) phases co-exist. The apparent experimental simplicity of this system which permits the localisation of the fundamental unit of electrical change in dilute solutrons, and its itineracy in concentrated solutions, has attracted a considerable amount of study from both chemists and physicists during the last 100 years.In this article we discuss the recent advances made not only in the study of metals in liquid ammonia, but also in solutions of metals in various other solvents, for example, amines and ethers. The review attempts to cover the properties of metal solutions in the dilute and concentrated ranges, as well as the nature of the Metal-non-Metal transition in these systems.

Structure of Solutions of Lithium in Methylamine across the Metal−Nonmetal Transition

“…On addition of lithium to methylamine, a shift occurs in the principal F ( k ) peak position from 1.75(2) Å -1 for the pure solvent to 1.63(2) and 1.62(2) Å -1 for lithium−methylamine solutions at 14.5 and 18 MPM, respectively. This shift arises from the overall reduction in density from 0.74 to 0.60 g cm -3 as the solution expands to accommodate the excess electrons, which have a cavity radius of about 3.0 Å (Figure ). − In addition, the solution F ( k )'s show a first sharp diffraction peak at 0.88(2) Å -1 at both concentrations . This peak corresponds to a real-space distance r = 2π/ k = 7.13 Å.…”

“…Saturated solutions of lithium in methylamine have a concentration of 22 MPM (Figure ) and electrical conductivity, σ, of approximately 400 Ω -1 cm -1 . This value of σ, which lies just above the predicted minimum for metallic states, implies a solution in the strongly scattering regime of metallic behavior. − In contrast to this, the transition occurs at 4 MPM for lithium−ammonia solutions, for which the saturation conductivity is also 40 times higher . Lithium−methylamine solutions therefore provide a unique opportunity to study electron localization and the M−NM transition in a lower dielectric solvent (ε r = 9.4), in which there is a high ratio of metal (and excess electrons) to solvent molecules.…”

“…Lithium dissolves readily in methylamine to produce metastable “metal solutions” which contain a rich variety of solvated ionic and electronic species. − The idea of solvating fundamental particles is indeed remarkable, and this in turn gives rise to intriguing thermodynamic, electrical, and magnetic properties. These include a time-honored metal−nonmetal (M-NM) transition, very low density (Figure ), and high redox reactivity. −

1 Molecular graphics snapshot obtained from classical simulations of pure methylamine (upper) and 18 MPM solution of lithium in methylamine (lower), showing the expansion due to the solvation of excess electrons (densities are 0.74 and 0.60 g cm -3 , respectively) . Color code: green, nitrogen; gray, hydrogen; slate, carbon; red, lithium.

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“…The liquid region of the lithium−methylamine phase diagram can be broadly divided into three composition dependent regimes. − Dilute solutions, below about 0.1 mole percent metal (MPM), are electrolytic and contain dissociated solvated cations and electrons. The latter occupy polaronic solvent cavities of approximate radius 3 Å and give the solutions their characteristic deep-blue color . Concentrated solutions, up to about 14 MPM, are dominated by diamagnetic electron pairs (bipolarons) and higher order clusters.…”

Biomimetic polyesters and their role in ion transport across cell membranes.

“…The preparation of the first one was based on discoveries of Dye [13] and Edwards [14] concerning the dissolution of alkali metals: potassium or sodium in an aprotic solvent, such as THF, containing a macrocyclic organic ligand e.g. 18-crown-6 or cryptand [2.2.2].…”