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Guest Molecules in a Layered Microporous Tin(IV) Phosphonate–Phosphate Material: Solid State NMR Studies

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journal contribution
posted on 30.11.2018, 00:00 by Vladimir I. Bakhmutov, Douglas W. Elliott, Aida R. Contreras, Abraham Clearfield
There is little systematic understanding of pore surfaces in layered microporous metal­(IV) phosphate–phosphonate materials and their interactions with guest molecules. In this paper, we show how to probe the mobility of guest molecules in such poorly crystalline systems using multinuclear solid-state NMR and relaxation time measurements. Anisotropic motions of benzene-d6 molecules absorbed on the pore walls of material Sn­(O3PC6H4PO3)0.85(O3POH)0.33 (1) have been recognized as the fast in-plane C6 rotation due to metal−π interactions with pore walls. The benzene-d6 absorption enthalpy due to Sn···π interactions has been determined as –ΔH = 5.9 kcal/mol. Specific interactions between pyridine and the pore walls of 1 have been observed as immobile pyridine, the population of which grows strongly at low temperatures to show thermodynamic parameters −ΔH of 5.0 kcal/mol and ΔS of −11.0 e.u. It has been suggested that these parameters characterize N···H–OP hydrogen bonding as a driving force for accumulation of immobile pyridine molecules in pores of compound 1.