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11B Nuclear Spin-Electron Spin Interactions in 11B MAS NMR Spectra of Paramagnetic Metal Borohydrides

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Isotropic and anisotropic couplings between the 11B nuclear spin and the electron spin of paramagnetic electrons are observed in 11B MAS NMR spectra of α-Pr(BH4)3 and LiCe(BH4)3Cl. The 11B NMR spectra of the central and satellite transitions are strongly influenced by the anisotropic nuclear spin-paramagnetic electron spin dipole-dipole interaction, which affects the spectra in a similar manner as the 11B chemical shift anisotropy. The 11B MAS NMR spectra are analyzed numerically, considering the quadrupole interaction and the anisotropic paramagnetic electron-nuclear spin dipole coupling along with the relative orientation of the two tensorial interactions. The observed isotropic shifts (δobs) show a linear dependency with the inverse temperature for both compounds, indicating that δobs is dominated by the contribution from the isotropic hyperfine shift. A similar temperature dependency is observed for the paramagnetic shift anisotropy for α-Pr(BH4)3. The isotropic and anisotropic paramagnetic interactions are approximately 5 and 4 times larger for α-Pr(BH4)3 as compared to LiCe(BH4)3Cl. This reflects mainly the difference in electron spin for the Pr3+ and Ce3+ ions and that the B site in α-Pr(BH4)3 has two Pr3+ ions within a 3 Å distance, whereas boron in LiCe(BH4)3Cl only has a single Ce3+ site within this distance.

Original languageEnglish
JournalJournal of Physical Chemistry C
Pages (from-to)1113-1124
Number of pages12
Publication statusPublished - Jan 2021

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