Hydrogen Environments In Low-OH, F, Cl Apatites Revealed By Double Resonance Solid-State NMR

Abstract

A series of hexagonal low-OH, F, Cl apatite compositions synthesized by high-temperature reaction is characterized by powder X-ray diffraction (PXRD) and 1H magic-angle spinning (MAS) solid-state NMR methods. Quantitative 1H NMR analysis indicates that the hydroxyl content in all samples is low, less than 2 mol percent, and is due to OH in apatite. 1H{31P} rotational echo double resonance (REDOR) NMR difference spectroscopy indicates that hydroxyl groups are preferentially oriented toward fluorine, probably because of OH–···F– hydrogen bonding. Clustered hydroxyl groups are also observed and may play a significant role in hexagonal solid solution for ternary F, OH, Cl apatites.