Dynamics and disposition of benzene guest molecules in the micropore channels of a flexible metal-organic framework studied by 2H NMR and X-ray crystallography

• Published in: Microporous and mesoporous materials Vol. 73; no. 1; pp. 71 - 79
• Main Authors: Ratcliffe, C.I., Soldatov, D.V., Ripmeester, J.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.08.2004; Elsevier
• Subjects: 2H NMR; Chemistry; Colloidal state and disperse state; Coordination polymer; Exact sciences and technology; General and physical chemistry; Guest dynamics; Ion-exchange; Metal-organic framework; Organic zeolites; Porous materials; Surface physical chemistry; Zeolites: preparations and properties; 2H NMR; Metal-organic framework; Coordination polymer; Organic zeolites; Guest dynamics; Micropore; Hybrid material; Polymer; X ray; NMR spectrometry; Transition metal Complexes; Zeolite; Porous material; Crystallography; Copper Complexes; X ray diffraction; Molecular sieve; Microporosity; Open framework; Dynamics; Benzene
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2003.11.020

The dynamics and disposition of benzene guest molecules included in the microporous channel structure of β-[CuL 2] (L is 1,1,1-trifluoro-5,5-dimethyl-5-methoxyacetylacetonate, {CF 3COCHCOC(CH 3) 2OCH 3} −) 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 (⊥), while the molecules in the narrower channel site are almost aligned along the channel (∥) 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 ⊥ and ∥ sites in about a 1:2 ratio, suggesting an energetic preference for the smaller site. 2H NMR spectra of C 6D 6 were obtained for the 100% occupancy sample as a function of temperature. The lines are skewed slightly by paramagnetic interactions with the Cu II 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 ⊥ and ∥ 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 ⊥:∥ ratio results in progressive line narrowing.