title: 19F/29Si rotational-echo double-resonance and heteronuclear spin counting under fast magic-angle spinning in fluoride-containing octadecasil.
abstract: 19F/29Si rotational-echo double-resonance (REDOR) and theta-REDOR NMR techniques have been applied under fast magic-angle spinning to a powder sample of fluoride-containing octadecasil. Efficient dipolar recoupling was observed and the effect of finite pulse lengths was found to be negligible using standard radiofrequency field strengths. Moreover, the determined internuclear distance of the 19F-29Si spin pairs formed by the silicons in the D4R units (T-1 site) and the fluoride anions is in very good agreement with previous REDOR and Hartmann-Hahn cross-polarization measurements. Numerical simulation of the REDOR dephasing curves at both the T-1 and T-2 sites considering all fluoride anions in the infinite solid lattice clearly confirm the X-ray crystal structure of octadecasil. Heteronuclear spin-counting theta-REDOR experiments are found to be very useful to obtain direct insight into the local network of dipolar interactions. Indeed, while 19F-29Si pair-like behavior is confirmed at the T-1 site, multiple dipolar interactions are clearly evidenced at the T-2 site.
authors.affiliation: Institut de Chimie, FRE 2446 CNRS, Université Louis Pasteur, BP 296, 67008 Strasbourg Cedex, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Bertani
authors.forename: Jésus
authors.initials: J
authors.lastname: Raya
authors.forename: Jérĵme
authors.initials: J
authors.lastname: Hirschinger
mesh_terms: D003198:Computer Simulation; D005459:Fluorides / Q000737:chemistry*; D005461:Fluorine; D007554:Isotopes; D008958:Models, Molecular; D008962:Models, Theoretical; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D012399:Rotation; D012680:Sensitivity and Specificity; D012825:Silicon; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D007554:Isotopes; C026679:octadecylsilica; D005461:Fluorine; D012822:Silicon Dioxide; D005459:Fluorides; D012825:Silicon