Orientation and Motion of Tetrahydrofuran in Graphite Intercalation Compounds: Proton NMR Studies of Cs(THF)1.3C24 and K(THF)2.5C24

Abstract

The orientation and motion of tetrahydrofuran (THF) in the ternary graphite intercalation compounds Cs(THF){sub 1.3}C{sub 24} and K(THF){sub 2.5}C{sub 24} have been studied by proton NMR. Simulations of the NMR spectra indicate that the THF molecules in Cs(THF){sub 1.3}C{sub 24} have their mean planes oriented parallel to the layers of the host lattice, while the THF molecules in K(THF){sub 2.5}C{sub 24} have their mean planes oriented at an angle between 50{degree} and 75{degree} from the graphite layers. The proton NMR spectra of both compounds show evidence that the THF molecules rotate about the normal to the graphite layers and confirm X-ray diffraction studies showing a degree of orientational disorder in the samples, corresponding to a mosaic spread in the graphite layer orientation. 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 A and to undergo nearly free pseudorotation through a series of conformations. Best agreement between simulated and experimental NMR spectra of Cs(THF){sub 1.3}C{sub 24} was obtained with THF interconverting between two conformations of C{sub s} symmetry and a puckering amplitude of 0.30 A. 31 refs., 15 figs.