Metal Transition in Sodium–Ammonia Nanodroplets

Hartweg, Sebastian; West, Adam H. C.; Yoder, Bruce L.; Signorell, Ruth

doi:10.1002/ange.201604282

Cited by 5 publications

(2 citation statements)

References 43 publications

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“…Solvated electrons can be generated simply by adding an alkali metal to anhydrous liquid ammonia; the solvated electrons have lifetimes on the order of months for solutions which are free from oxygen and moisture. It can be expected that photoelectron (PE) spectroscopy of these liquid solutions may reveal insights as to the binding energies of different electron motifs in ammonia. , However, in a recent review of the spectroscopy of excess electrons in ammonia it is remarked that the electronic structure of neat liquid ammonia itself has not as yet been characterized through its photoelectron spectrum, although the PE spectrum of large ammonia clusters and ammonia ice on MoS 2 has been reported. The liquid PE spectrum would be a crucial complement to the known ammonia orbital energies in both vapor and amorphous ice; it is certainly a necessary prerequisite for an understanding of the band gap in liquid ammonia and to provide a more rounded understanding of excess electrons in liquid ammonia.…”

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confidence: 99%

Valence and Core-Level X-ray Photoelectron Spectroscopy of a Liquid Ammonia Microjet

et al. 2019

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Photoelectron spectroscopy of microjets expanded into vacuum allows access to orbital energies for solute or solvent molecules in the liquid phase. Microjets of water, acetonitrile and alcohols have previously been studied; however, it has been unclear whether jets of low temperature molecular solvents could be realized. Here we demonstrate a stable 20 μm jet of liquid ammonia (−60 °C) in a vacuum, which we use to record both valence and core-level band photoelectron spectra using soft X-ray synchrotron radiation. Significant shifts from isolated ammonia in the gas-phase are observed, as is the liquid-phase photoelectron angular anisotropy. Comparisons with spectra of ammonia in clusters and the solid phase, as well as spectra for water in various phases potentially reveal how hydrogen bonding is reflected in the condensed phase electronic structure.

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Valence and Core-Level X-ray Photoelectron Spectroscopy of a Liquid Ammonia Microjet

et al. 2019

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“… 2 The dissolution and reduction process is facilitated by strong stabilization of the alkali cation by preorganized complexants such as crown ethers and cryptands. 3 This enables alkali metals to be dissolved in even weakly polar solvents such as tetrahydrofuran (THF) by formation of alkalide anions that persist in the absence of any better electron receptor, as with ammonia or small amines (metal–ammonia solutions 4 − 6 and solutions containing solvated electrons 7 , 8 ), functional groups in organic or organometallic molecules (the dissolving metal reduction), or simply a different, more reducible metal. Cryogenic temperatures are also necessitated to avoid reduction and decomposition of solvent.…”

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confidence: 99%

Superalkali–Alkalide Interactions and Ion Pairing in Low-Polarity Solvents

et al. 2021

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The nature of anionic alkali metals in solution is traditionally thought to be “gaslike” and unperturbed. In contrast to this noninteracting picture, we present experimental and computational data herein that support ion pairing in alkalide solutions. Concentration dependent ionic conductivity, dielectric spectroscopy, and neutron scattering results are consistent with the presence of superalkali–alkalide ion pairs in solution, whose stability and properties have been further investigated by DFT calculations. Our temperature dependent alkali metal NMR measurements reveal that the dynamics of the alkalide species is both reversible and thermally activated suggesting a complicated exchange process for the ion paired species. The results of this study go beyond a picture of alkalides being a “gaslike” anion in solution and highlight the significance of the interaction of the alkalide with its complex countercation (superalkali).

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Electron Solvation and the Unique Liquid Structure of a Mixed‐Amine Expanded Metal: The Saturated Li–NH₃–MeNH₂ System

et al. 2017

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Metal-amine solutions provideaunique arena in which to study electrons in solution, and to tune the electron density from the extremes of electrolytic through to true metallic behavior.The existence and structure of anew class of concentrated metal-amine liquid, Li-NH 3 -MeNH 2 ,i sp resented in which the mixed solvent produces an ovel type of electron solvation and delocalization that is fundamentally different from either of the constituent systems.N MR, ESR, and neutron diffraction allowt he environment of the solvated electron and liquid structure to be precisely interrogated. Unexpectedly it was found that the solution is truly homogeneous and metallic.Equally surprising was the observation of strong longer-range order in this mixed solvent system. This is despite the heterogeneity of the cation solvation, and it is concluded that the solvated electron itself acts as as tructural template.This is aquite remarkable observation, given that the liquid is metallic.Alkali metals demonstrate an exceptional solubility in NH 3 , yielding intensely colored conducting solutions that have fascinated chemists since the time of Sir Humphry Davy. [1,2] Va rying the concentration of metal in these liquids dramatically alters the electronic,magnetic,and structural properties of the solutions,a nd enables us to experimentally determine the manner in which liquid systems accommodate excess electron density.A talow concentration of metal/electrons, the solutions are electrolytic, whereby the metal valence electrons have been ionized into solution and exist as solvated electrons propagating between solvent cavities.[3] Increasing the concentration results in metallization in the liquid phase, which for the Li À NH 3 system occurs at amere 4mol %metal (MPM).[2] Interestingly at lower temperatures,b elow T C = 210 K, the point of the Mott-type metal-insulator transition (MIT) is obscured by ap ronounced liquid-liquid phase separation.[2] This illustrates that the localized and delocalized electron states do not readily co-exist, which is dramatically manifested by the fact that the more concentrated metallic solution floats above the dilute electrolytic phase for T < T c .[2,4] Above 8MPM the solutions do not exhibit phase separation, appearing golden up to the concentration limit of 20 MPM, [5] thee xpanded metal Li(NH 3 ) 4 . [6,7] Thec oncentration and temperature dependence of this liquid-liquid phase separation has been mapped through multi-element NMR spectroscopy. [8] Along with metal concentration, chemical tunability of the electronic properties of these systems can be achieved by varying the amine.L ithium will also dissolve in MeNH 2 to yield as ystem whereby solvated electrons transition to am etallic state. [3,[9][10][11][12] TheM IT in Li-MeNH 2 occurs at 15 MPM, an otably higher concentration than in Li-NH 3 . No liquid-liquid phase separation has been detected across the full concentration range of Li-MeNH 2 ,a nd the solution remains ad eep blue,a lbeit with am etallic luster. The conductivity of liqui...

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Metal Transition in Sodium–Ammonia Nanodroplets

Cited by 5 publications

References 43 publications

Valence and Core-Level X-ray Photoelectron Spectroscopy of a Liquid Ammonia Microjet

Valence and Core-Level X-ray Photoelectron Spectroscopy of a Liquid Ammonia Microjet

Superalkali–Alkalide Interactions and Ion Pairing in Low-Polarity Solvents

Electron Solvation and the Unique Liquid Structure of a Mixed‐Amine Expanded Metal: The Saturated Li–NH₃–MeNH₂ System

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Metal Transition in Sodium–Ammonia Nanodroplets

Cited by 5 publications

References 43 publications

Valence and Core-Level X-ray Photoelectron Spectroscopy of a Liquid Ammonia Microjet

Valence and Core-Level X-ray Photoelectron Spectroscopy of a Liquid Ammonia Microjet

Superalkali–Alkalide Interactions and Ion Pairing in Low-Polarity Solvents

Electron Solvation and the Unique Liquid Structure of a Mixed‐Amine Expanded Metal: The Saturated Li–NH3–MeNH2 System

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Electron Solvation and the Unique Liquid Structure of a Mixed‐Amine Expanded Metal: The Saturated Li–NH₃–MeNH₂ System