The Absorption Spectra of the Blue Solutions of Certain Alkali and Alkaline Earth Metals in Liquid Ammonia and in Methylamine.

Gibson, G. E.; Argo, W. L.

doi:10.1021/ja02242a003

Cited by 47 publications

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“…This is the first time the term "solvated electrons" was invoked. They first favored (b), but subsequently [16] came to the firm conclusion that the blue color is due to solvated electrons.…”

Section: Chemical and Physical Properties Of Metal-ammonia Solutionsmentioning

confidence: 99%

A Molecular Perspective on Lithium–Ammonia Solutions

2009

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A detailed molecular orbital (MO) analysis of the structure and electronic properties of the great variety of species in lithium-ammonia solutions is provided. In the odd-electron, doublet states we have considered: e-@(NH3)n (the solvated electron, likely to be a dynamic ensemble of molecules), the Li(NH3)4 monomer, and the [Li(NH3)4+.e-@(NH3)n] ion-pairs, the Li 2s electron enters a diffuse orbital built up largely from the lowest unoccupied MOs of the ammonia molecules. The singly occupied MOs are bonding between the hydrogen atoms; we call this stabilizing interaction H-->H bonding. In e-@(NH3)n the odd electron is not located in the center of the cavities formed by the ammonia molecules. Possible species with two or more weakly interacting electrons also exhibit H-->H bonding. For these, we find that the singlet (S=0) states are slightly lower in energy than those with unpaired (S=1, 2...) spins. TD-DFT calculations on various ion-pairs show that the three most intense electronic excitations arise from the transition between the SOMO (of s pseudosymmetry) into the lowest lying p-like levels. The optical absorption spectra are relatively metal-independent, and account for the absorption tail which extends into the visible. This is the source of Sir Humphry Davy's "fine blue colour" first observed just over 200 years ago.

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Section: Chemical and Physical Properties Of Metal-ammonia Solutionsmentioning

confidence: 99%

A Molecular Perspective on Lithium–Ammonia Solutions

2009

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“…The measurements of paramagnetic resonance absorption are consistent with the existence of trapped electrons (4). Finally, the absorption spectra of a number of the solutions have been measured, and the observation made that in ammonia there is a single absorption maximum whose position is independent of the particular metal in solution (1,9). This maximum is in a region where none appears in the spectrum of bullr sodium metal; ancl in the spectrum of atomic sodium, very strong absorption occurs a t 5889 i % (D line), which does not appear in the solution spectrum.…”

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confidence: 53%

Absorption Spectra of Metals in Solution

Blades¹,

Hodgins²

1955

Can. J. Chem.

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Measureme~lts of the absorption spectra were made on solutions of allcali and allcaline earth metals in ammonia, methylamine, ethylarnine, and ~nixecl solvents. I n ammonia, a single absorption band was measured which is common to all the ~netals esamined. I n the arnines and in mixtures of arnlno~~ia mith methylamine, ho~vever, bands were found which were characteristic of the metal employed. h hypothesis has been advanced to explain the existence of the different types of energy traps responsible for the variations in spectra.The alliali metals ancl some of the a l l d i n e earth metals dissolve in liquid ammonia without reaction; it is thought that simple dissolution occurs, yielding metal ions and electrons xxrl~ich are trapped or solvated in the liquid (5). Various physical properties have been examined whiclz are consistent mith this postulate, although a concise model has not yet been formulated for the electron traps. For example, the expansion exhibited on dissolving the metal has been attributed t o the formation of holes in the liquid which represent energy barriers for the escape of electrons (8). The electrical conductivity in dilute solution is greater than can be explained by simple ionic transport, but less than mould be expected by electronic conduction (5). Magnetic susceptibility measurements indicate that the metal is ionized, but some difficulty is experienced in explaining the variation of the susceptibility with temperature (3). The measurements of paramagnetic resonance absorption are consistent with the existence of trapped electrons (4). Finally, the absorption spectra of a number of the solutions have been measured, and the observation made that in ammonia there is a single absorption maximum whose position is independent of the particular metal in solution (1, 9). This maximum is in a region where none appears in the spectrum of bullr sodium metal; ancl in the spectrum of atomic sodium, very strong absorption occurs a t 5889 i % (D line), which does not appear in the solution spectrum. Since the maximum observed is also absent from the spectrum of sodium ion and of liquid ammonia, it has been ascribed t o the trapped electrons.Primary amines will also dissolve some of the metals; sodium, cesium, potassium, lithium, and calcium are soluble in methylamine, ~vhile ethylarnine dissolves a t least lithium and potassium. Although these solutions have been exaininecl lcss exhaustivelj. than the ammonia solutions, their behavior is similar. Thus the variation of electrical conductivity with concentration in metal solutions in methylamine is similar t o that in anhydrous alnmonia (2), and the absorption spectra, although exhibiting maxima a t a different wave l11hnzrscript

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“…Dies war das erste Mal, dass der Begriff "solvatisierte Elektronen" fiel. Gibson und Argo favorisierten zunächst (b), schlossen später [16] aber richtig, dass die blaue Farbe durch solvatisierte Elektronen verursacht wird.Mit allmählich steigender Metallkonzentration sinkt die ¾quivalentleitfähigkeit (ganz so wie bei gewöhnlichen Salzlösungen in Ammoniak) aufgrund der immer stärker werdenden Wechselwirkungen zwischen solvatisierten Elektronen und solvatisierten Kationen, die zur Bildung von Ionenpaaren M s + e s À führt. Bei noch höheren Konzentrationen von etwa 1 Mol-% des Metalls [17] (MPM) beginnen die solvatisierten Elektronen miteinander wechselzuwirken, und ihre Spins werden gepaart.…”

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Lithium‐Ammoniak‐Lösungen: eine molekulare Betrachtung

2009

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Dieser Aufsatz gibt eine detaillierte Molekülorbitalanalyse der Strukturen und elektronischen Eigenschaften der vielfältigen Spezies, die in Lithium‐Ammoniak‐Lösungen auftreten. Als Spezies mit ungerader Elektronenzahl (Dublett‐Zustände) betrachten wir: e−@(NH3)n (das solvatisierte Elektron, wahrscheinlich ein dynamisches Ensemble von Molekülen), das Li(NH3)4‐Monomer und die [Li(NH3)4+ ⋅ e−@(NH3)n]‐Ionenpaare. Das 2s‐Elektron des Li besetzt ein diffuses Orbital, das hauptsächlich von den niedrigsten unbesetzten Molekülorbitalen (MOs) der Ammoniakmoleküle gebildet wird. Die einfach besetzten MOs sind zwischen den Wasserstoffatomen bindend; wir bezeichnen diese stabilisierende Wechselwirkung als H H‐Brücke. Im e−@(NH3)n befindet sich das Überschusselektron nicht im Zentrum des von den Ammoniakmolekülen gebildeten Käfigs. Denkbare Spezies mit zwei oder mehr schwach wechselwirkenden Elektronen bilden ebenfalls H H‐Brücken. Für diese Spezies finden wir, dass die Singulett‐Zustände (S=0) bei etwas tieferer Energie liegen als die Zustände mit ungepaarten Spins (S=1, 2…︁). TD‐DFT‐Rechnungen an verschiedenen Ionenpaaren zeigen, dass die drei intensivsten elektronischen Anregungen von den Übergängen aus dem SOMO (mit s‐Pseudosymmetrie) in die niedrigsten p‐artigen Niveaus stammen. Die optischen Absorptionsspektren sind weitgehend unabhängig vom Metall, und wir können die in das Sichtbare reichende Absorptionsflanke gut erklären. Letztere verursacht die “schöne blaue Farbe”, die Sir Humphry Davy vor 200 Jahren erstmals beobachtete.

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The Absorption Spectra of the Blue Solutions of Certain Alkali and Alkaline Earth Metals in Liquid Ammonia and in Methylamine.

Cited by 47 publications

References 0 publications

A Molecular Perspective on Lithium–Ammonia Solutions

A Molecular Perspective on Lithium–Ammonia Solutions

Absorption Spectra of Metals in Solution

Lithium‐Ammoniak‐Lösungen: eine molekulare Betrachtung

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