Characterizing the excess electron of Li(NH3)4

Abstract

Small lithium ammonia clusters are model systems for the dissociation of metals into solvated cations and electrons in ammonia. Metal-ammonia solutions display a complex behavior with increasing metal concentration including a phase change from a paramagnetic to a metallic diamagnetic phase, and small clusters should be useful models in the low concentration regime, where one may expect the ammoniated electron to show a behavior similar to that of the hydrated electron. Yet, even in the low concentration regime the nature of the ammoniated electron is still controversial with cavity models supported by optical and density measurements whereas localized radical models have been invoked to explain magnetic measurements. Small clusters can shed light on these open questions, and in particular the Li-NH(3) tetramer represents the smallest cluster with a complete solvation shell for the Li(+) cation. In view of the controversies about the character of the excess electron, the first question investigated is whether different theoretical characterizations of the "excess electron" lead to different conclusions about it. Only small differences are found between orbital-based and spin density-based and between self-consistent-field and coupled-cluster-based methods. Natural orbitals from equation-of-motion coupled-cluster calculations are then used to analyze the excess electron's distribution of Li(NH(3))(4) with particular emphasis on the portion of the excess electron's density that is closely associated with the N atoms. Three different comparisons show that only about 6% of the excess electron's density are closely associated with the atoms, with about 1% being closely associated with any N atom, and that the electron is best characterized as a Rydberg-like electron of the whole cluster. Finally, it is shown that in spite of the small amount of density close to the N atoms, the spin-density at the N nuclei is substantial, and that the magnetic observations can plausibly be explained within the cavity model.

Excited State Trends in Bidirectionally Expanded Closed-Shell PAH and PANH Anions

“…[5][6][7][8] Such states are known for various organic molecular anions. 3,4,[9][10][11][12][13][14][15][16][17][18][19][20][21] Some of these so-called dipole-bound excited states have even been suggested to explain longstanding interstellar phenomena. [22][23][24][25] However, the additional valence excited state below such a near-continuum state, whether dipole-bound or nearly electron-removed, is exceptionally rare.…”

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

“…All metallic metal amines share the trait of being highly structured liquids,13, 14, 15, 16 with distinct M (solv) –M (solv) correlations. In both Li–NH 3 and Li–MeNH 2 solutions, Li is found to be four‐coordinate, which has subsequently been found to be the case in the gas phase,17, 18, 19 and through computational investigation 1, 19, 20, 21. The volumetric expansion of these liquid metals across their insulator–metal transition is also accompanied by the appearance of void spaces, which is presumably linked to the conduction electron density.…”

“…[13,14] All metallic metal amines share the trait of being highly structured liquids, [13][14][15][16] with distinct M (solv) -M (solv) correlations.I nb oth Li-NH 3 and Li-MeNH 2 solutions,L ii s found to be four-coordinate,w hich has subsequently been found to be the case in the gas phase, [17][18][19] and through computational investigation. [1,[19][20][21] Thevolumetric expansion of these liquid metals across their insulator-metal transition is also accompanied by the appearance of void spaces,which is presumably linked to the conduction electron density.I nLi-NH 3 these voids take the form of channels between Li(NH 3 ) 4 units, [13] whereas in Li(MeNH 2 ) 4 the voids are spatially isolated. [14] This is concordant with magnetic measurements that suggest electronic conduction in Li(MeNH 2 ) 4 is via rapid migration of electrons between these polaronic voids,w hich begin to localize in the solid state.…”

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

“…All metallic metal amines share the trait of being highly structured liquids, with distinct M (solv) –M (solv) correlations. In both Li–NH 3 and Li–MeNH 2 solutions, Li is found to be four‐coordinate, which has subsequently been found to be the case in the gas phase, and through computational investigation . The volumetric expansion of these liquid metals across their insulator–metal transition is also accompanied by the appearance of void spaces, which is presumably linked to the conduction electron density.…”