Local structure of nanoscopic magnesium hydroxide fluorides studied by natural abundance ~(25)Mg solid state NMR spectroscopy

摘要

Along with X-ray diffraction measurements, ~(25)Mg solid state NMR experiments were performed in natural abundance at 9.4 T on crystalline and mechanically milled samples of MgO, Mg(OH)_2, MgF_2, and magnesium hydroxide fluorides Mg(OH)_xF_(2-x) prepared on mechanochemical and sol-gel syntheses routes. In addition to single pulse and spin-echo sequences, both static ~1H-~(25)Mg CP and ~(19)F-~(25)Mg CP measurements allowed the registration of ~(25)Mg spectra in attractive short measurement times. Although an assignment of different magnesium species in magnesium hydroxide fluorides is only hardly possible, position and line shapes of ~(25)Mg spectra of magnesium hydroxide fluorides reflect chemically reliable trends. All samples studied here show a sixfold fluorine, oxygen, or mixed fluorine / oxygen coordination of magnesium, also in highly disordered samples.