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 ap… Show more
“…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.…”
Section: Resultsmentioning
confidence: 98%
“…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.…”
Section: Introductionmentioning
confidence: 92%
“…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. − …”
Section: Introductionmentioning
confidence: 99%
“…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.…”
We present the first neutron diffraction studies of the structure of lithium-methylamine solutions as they cross the metal-nonmetal transition. A shift in the principle scattering peak immediately reflects the overall decrease in density as the solvent expands to accommodate the excess electrons. 6 Li/ 7 Li isotopic labeling then allows us to answer key questions concerning cation solvation. We find that each lithium cation is coordinated to four methylamine molecules. However, the cation solvation shell expands as the system becomes metallic: a direct structural signature of electron delocalization. As a result of correlations between strongly solvated lithium ions, the solutions are highly structured over intermediate length scales. The valence electrons then reside primarily in polaronic cavities, formed by the solvated cations and remaining solvent molecules.
“…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.…”
Section: Resultsmentioning
confidence: 98%
“…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.…”
Section: Introductionmentioning
confidence: 92%
“…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. − …”
Section: Introductionmentioning
confidence: 99%
“…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.…”
We present the first neutron diffraction studies of the structure of lithium-methylamine solutions as they cross the metal-nonmetal transition. A shift in the principle scattering peak immediately reflects the overall decrease in density as the solvent expands to accommodate the excess electrons. 6 Li/ 7 Li isotopic labeling then allows us to answer key questions concerning cation solvation. We find that each lithium cation is coordinated to four methylamine molecules. However, the cation solvation shell expands as the system becomes metallic: a direct structural signature of electron delocalization. As a result of correlations between strongly solvated lithium ions, the solutions are highly structured over intermediate length scales. The valence electrons then reside primarily in polaronic cavities, formed by the solvated cations and remaining solvent molecules.
“…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].…”
Syntheses of biomimetic low-molecular weight poly-(R)-3-hydroxybutanoate mediated by three types of supramolecular catalysts are presented. The utility of these synthetic polyesters for preparation of artificial channels in phospholipid bilayers capable of sodium and calcium ion transport across cell membranes, is discussed. Further studies on possible applications of these bio-polymers for manufacturing drugs of prolonged activity are under way.
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