| Abstract | The dynamics and disposition of benzene guest molecules included in the microporous channel structure of [beta]-[CuL2] (L is 1,1,1-trifluoro-5,5-dimethyl-5-methoxyacetylacetonate, {CF3COCHCOC(CH3)2OCH3}-) were studied as a function of temperature and total guest content. Two samples, with ~100% and ~35% of the sorption sites in the channels occupied by benzene, were studied with single-crystal XRD at 173 K. In the fully occupied sample, the benzene molecules are located in the alternating broader and narrower wide portions of the channels, and these sites are populated nearly equally, producing dense 1D packing of the guest molecules along the channel. The molecules in the broader channel site are almost perpendicular to the channel axis ([perpendicular]), while the molecules in the narrower channel site are almost aligned along the channel ([short parallel]) with their thermal parameters about twice as large. In the sample with 35% occupancy, the benzenes have thermal parameters that are twice those in the fully occupied sample and are distributed over [perpendicular] and [short parallel] sites in about a 1:2 ratio, suggesting an energetic preference for the smaller site. 2H NMR spectra of C6D6 were obtained for the 100% occupancy sample as a function of temperature. The lines are skewed slightly by paramagnetic interactions with the CuII centers. Line shape analysis indicated a sequence of three types of benzene motion with increasing temperature: there is already rapid in-plane motion at 77 K, followed at slightly higher temperatures by the onset of 2-site jumps between the [perpendicular] and [short parallel] orientations. Before this reaches the fast motion limit, the onset of reorientation about the 3-fold axis of the channel commences in the 175 K region. At room temperature all of these dynamic processes are rapid, as they are for samples with lower benzene loadings, but in these cases the reduced [perpendicular]:[short parallel] ratio results in progressive line narrowing. |
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