NMR Study of Lithium Dynamics and Molecular Motions in a Diethylamine−Molybdenum Disulfide Intercalation Compound

Abstract

Measurements of the 13C, 7Li, and 1H nuclear magnetic resonance (NMR) of the nanocomposite formed by the intercalation of lithium and diethylamine in molybdenum disulfide, Li0.1MoS2[(C2H5)2NH]0.2, are reported. The strong Li−Li dipolar interaction strength, calculated from the 7Li NMR decoupling data, suggests the formation of lithium clusters. The dimensional restriction of the available space between the host layers supports a hypothesis that is based on the formation of Li3 clusters stabilized by amine ligands. The lithium relaxation is mainly due to the interaction between the quadrupolar moment of the 7Li nuclei and the fluctuating electric field gradient at the site of the nucleus, produced by the surrounding charge distribution. The dynamical parameters obtained from the 7Li temperature dependence of the spin−lattice relaxation indicate a high lithium mobility, which is attributed to the fast exchange motion of the lithium ions between the coordination sites within each Li3 aggregate. The 1H line shape and relaxation data support the proposed structural model for the lithium−diethylamine cluster. Numerical analysis of the 1H line shape indicates that the intercluster dipole−dipole interactions are responsible for most of the spectral broadening. 1H spin−lattice relaxation is mainly governed by hydrogen nuclei in the less-mobile CH2 and in the fast-relaxing CH3 groups in the diethylamine molecule.

Lithium dynamics in molybdenum disulfide intercalation compounds studied by nuclear magnetic resonance

“…The numerical analysis of the experimental 1 H spectra performed on the basis of the chemical structure of the diethylamine cluster, constituted by the arrangement of NH, CH 2 and CH 3 groups, indicates that the inter-cluster dipole-dipole interactions are responsible for most of the spectral broadening. The second moments parameters determined from the 1 H line-shape analysis were found to be consistent with the measured proton spinlattice relaxation times [18].…”

“…In the case of the [d-eth] nanocomposite, for example, the formation of a triangular Li 3 species stabilized by amine ligands, with Li-Li distance of about 2.8 A, was proposed (Fig. 2) [18]. The lithium's tendency to form clusters is well known and the formation of lithium-rich nanoclusters has been reported in several lithium intercalated materials [22][23][24].…”

“…Further details of the sample preparation procedure are given elsewhere [18,19]. The 7 Li NMR measurements were performed on a Varian-400 MHz INOVA spectrometer operating at 155.4 MHz using a wide line Varian probe in the temperature range 140-353 K. The static 7 Li lineshape was ob-tained from the Fourier transform of the decaying part of the quadrupolar echo.…”

“…1, which is a reasonable measurement of the theoretical satellites separation. The quadrupole coupling constant (e 2 qQ/ ) is then estimated to be of the order of 60 kHz [18]. The quadrupolar constant in Eq.…”

“…In a previous study we reported a carbon ( 13 C), proton ( 1 H) and lithium ( 7 Li) NMR investigation of the nanocomposite formed by the intercalation of lithium and diethylamine into molybdenum disulphide, Li 0.1 MoS 2 [C 4 H 10 NH] [18]. Here, we extend this study to include the nanocomposites prepared with larger amines, such as C 8 H 18 NH (dibutylamine) and C 10 H 22 NH (dipentylamine).…”