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