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Nuclear magnetic resonance structural investigations of ammonia-doped fullerides

Nuclear magnetic resonance structural investigations of ammonia-doped fullerides
Nuclear magnetic resonance structural investigations of ammonia-doped fullerides
The dynamic and structural properties of the ammonia-doped superconducting fulleride (NH3)(x)NaK2C60 (0.5 <= x <= 1), well known for its anomalous decrease of transition temperature with doping, have been investigated using sodium and deuterium solid-state NMR techniques. The independence of Na-23 quadrupole splitting from the ammonia content x, which, at the same time, substantially affects T-c, suggests a marginal role of the cation position in the superconducting mechanism. On the other hand, a strong reduction of the deuterium quadrupole coupling with respect to the free ammonia value denotes the presence of weak hydrogen bonds between the deuterium atoms and fullerene pi orbitals. Despite the bond weakness, as evinced by the lively ammonia rotational dynamics even at very low temperatures, the resulting electron localization could explain the observed T-c anomaly. The motion of the ND3-Na group (located in the compound's octahedral voids), as well as the evolution of the ammonia dynamics as a function of temperature, were determined from deuterium NMR line shape analysis and from detailed numerical simulations. While at the lowest measured temperatures only the ammonia rotation around its own C-3 axis takes place, above similar to 25 and 70 K, respectively, also the wobbling of the C-3 axis and the ND3 relocation become active, successfully modeled by a strongly correlated motion involving two different time scales.
na-23 nmr-spectroscopy, noise excitation, line-shapes, superconductivity, transition, deuterium, dynamics, solids, intercalation, molecules
0021-9606
1-10
Shiroka, T.
b4f908a7-22a8-4069-98dc-bdac6ea4f721
Fumera, G.
040113af-adba-4a4e-b58b-5008f59501a4
Ligabue, O.
280d5b21-aca9-4024-b98b-e5e25f2cd944
Riccò, M.
9311bb7c-3694-441c-a1aa-a50508c2d2a1
Antonioli, G.C.
3680de2d-a879-403b-9e92-f81282100a07
Shiroka, T.
b4f908a7-22a8-4069-98dc-bdac6ea4f721
Fumera, G.
040113af-adba-4a4e-b58b-5008f59501a4
Ligabue, O.
280d5b21-aca9-4024-b98b-e5e25f2cd944
Riccò, M.
9311bb7c-3694-441c-a1aa-a50508c2d2a1
Antonioli, G.C.
3680de2d-a879-403b-9e92-f81282100a07

Shiroka, T., Fumera, G., Ligabue, O., Riccò, M. and Antonioli, G.C. (2006) Nuclear magnetic resonance structural investigations of ammonia-doped fullerides. The Journal of Chemical Physics, 124 (20), 1-10. (doi:10.1063/1.2198822).

Record type: Article

Abstract

The dynamic and structural properties of the ammonia-doped superconducting fulleride (NH3)(x)NaK2C60 (0.5 <= x <= 1), well known for its anomalous decrease of transition temperature with doping, have been investigated using sodium and deuterium solid-state NMR techniques. The independence of Na-23 quadrupole splitting from the ammonia content x, which, at the same time, substantially affects T-c, suggests a marginal role of the cation position in the superconducting mechanism. On the other hand, a strong reduction of the deuterium quadrupole coupling with respect to the free ammonia value denotes the presence of weak hydrogen bonds between the deuterium atoms and fullerene pi orbitals. Despite the bond weakness, as evinced by the lively ammonia rotational dynamics even at very low temperatures, the resulting electron localization could explain the observed T-c anomaly. The motion of the ND3-Na group (located in the compound's octahedral voids), as well as the evolution of the ammonia dynamics as a function of temperature, were determined from deuterium NMR line shape analysis and from detailed numerical simulations. While at the lowest measured temperatures only the ammonia rotation around its own C-3 axis takes place, above similar to 25 and 70 K, respectively, also the wobbling of the C-3 axis and the ND3 relocation become active, successfully modeled by a strongly correlated motion involving two different time scales.

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More information

Published date: 2006
Keywords: na-23 nmr-spectroscopy, noise excitation, line-shapes, superconductivity, transition, deuterium, dynamics, solids, intercalation, molecules
Organisations: Chemistry

Identifiers

Local EPrints ID: 44546
URI: http://eprints.soton.ac.uk/id/eprint/44546
ISSN: 0021-9606
PURE UUID: 8c0270ed-e8ac-4fa4-a724-b266871f0298

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Date deposited: 02 Mar 2007
Last modified: 13 Mar 2019 21:07

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