@article {335, title = {Diamagnetic clusters of paramagnetic endometallofullerenes: A solid-state MAS NMR study}, journal = {Journal of Physical Chemistry B}, volume = {108}, year = {2004}, note = {J Phys Chem B846BKTimes Cited:10Cited References Count:39}, month = {Aug 19}, pages = {12450-12455}, abstract = {
Solid powder samples of complexes of the endometallofullerenes (EMF) La@C-82 and Y@C-82 with hexamethylphosphoramide (HMPA) were studied by magic-angle spinning (MAS) NMR. We have obtained well-resolved P-31 NMR spectra and C-13 NMR spectra for both La-EMF/HMPA and Y-EMF/HMPA and La-139 spectra for the La-EMF/HMPA. The (31)p measurements on La-EMF/HMPA and Y-EMF/HMPA have revealed considerable chemical shifts of (31)p signals relative to pure HMPA. Two-dimensional exchange P-31 experiments revealed that HMPA molecules at different sites in the EMF/HMPA complex do not change positions at a time scale of up to 1 s. Both EMF samples demonstrate a vast chemical shift range for 31p of the bound HMPA molecules. In addition, the La-EMF/HMPA exhibits the enormous spreading of the chemical shifts for La-139. The experimental results suggest that paramagnetic La@C-82 and Y@C-92 in the solid state form clusters (nanoparticles) in which the exchange coupling of the EMF takes place with quenching of the most electron spins.
}, keywords = {complexes}, isbn = {1520-6106}, doi = {Doi 10.1021/Jp048610z}, url = {Dynamic NMR microscopy has been used to study xenon gas undergoing Poiseuille flow in the regime where deterministic and stochastic motions are the same order of magnitude. For short observation time, the flow profile images are largely influenced by the longitudinal diffusion, manifested by large displacements in both positive and negative directions. For longer observation time, the effect of the mixing between the fast and slow flow components due to transverse diffusion becomes apparent. A spin-echo version of the dynamic NMR experiment yields images exhibiting strong distortions for longer observation time due to fast diffusion under the \"natural\" gradient from magnetic field inhomogeneity (compared to results obtained with a stimulated echo version). This effect is used as an edge-enhancement filter by employing a longer time duration of the imaging gradient in a stimulated echo experiment. (C) 2001 Academic Press.
}, keywords = {transport}, isbn = {1090-7807}, doi = {Doi 10.1006/Jmre.2000.2283}, url = {