ORIENTATION AND MOTION OF TETRAHYDROFURAN IN GRAPHITE-INTERCALATION COMPOUNDS - PROTON NMR-STUDIES OF CS(THF)(1.3)C-24 AND K(THF)(2.5)C-24

The orientation and motion of tetrahydrofuran (THF) in the ternary gra phite intercalation compounds Cs-(THF)(1.3)C-24 and K(THF)(2.5)C-24 ha ve been studied by proton NMR. Simulations of the NMR spectra indicate that the THF molecules in CS(THF)(1.3)C-24 have their mean planes ori ented parallel to the layers of the host lattice, while the THF molecu les in K(THF)(2.5)C-24 have their mean planes oriented at an angle bet ween 50 degrees and 75 degrees from the graphite layers. The proton NM R spectra of both compounds show evidence that the THF molecules rotat e about the normal to the graphite layers and confirm X-ray diffractio n studies showing a degree of orientational disorder in the samples, c orresponding to a mosaic spread in the graphite layer orientation. The conformation of the intercalated THF was studied by simulating the ex perimental NMR spectra using models for the conformational motion of T HF. Simulations indicate that the conformation of intercalated THF is different than gas or liquid phase THF, which has been found to have a ring puckering amplitude of 0.38-0.44 Angstrom and to undergo nearly free pseudorotation through a series of conformations. Best agreement between simulated and experimental NMR spectra of Cs(THF)(1.3)C-24 was Obtained with THF interconverting between two conformations of C-s sy mmetry and a puckering amplitude of 0.30 Angstrom. Free or slightly hi ndered pseudorotation of THF (observed in liquid or gaseous THF) in th is compound produces simulated spectra that differ significantly from the experimental spectra. Simulated proton NMR spectra of K(THF)(2.5)C -24 using conformations of C-s symmetry or free or slightly hindered p seudorotation of THF do not fit the experimental spectra sufficiently well to allow distinction between the conformational motions or to exc lude other possible motions.