NMRcrystallography of AlPO4-CJ2: from the topological network to the local (OH)/F distribution

Abstract

We present in this contribution the description of the structure of AlPO₄-CJ2 by NMR crystallography, from the main topological features to the very local order of the OH and F atoms. A whole range of 1D (¹⁹F, ³¹P, ²⁷Al) and 2D heteronuclear (²⁷Al–³¹P, ¹⁹F–²⁷Al, ¹⁹F–³¹P) and homonuclear (¹⁹F–¹⁹F and ³¹P–³¹P) NMR experiments with unprecedented resolution for AlPO₄-CJ2 are used to describe and quantify the various environments of the aluminium, phosphorus and fluorine atoms leading to the determination of the integrant unit and its distribution in the 3D space, which defines the topological network. Additional local information about the OH/F distribution in this sample, which cannot be accessed by the usual diffraction techniques, is also provided by the high-resolution of the solid-state NMR spectra presented in this work. The example of AlPO₄-CJ2 illustrates the importance of the high flexibility and versatility of the NMR experiment, which allows one to select the scale and the level of accuracy in the description of a structural model, together with the applicability of computational structure prediction methods once constituent building blocks are identified. This study, which lies in the frame of generalized crystallography, also highlights the value of providing an accurate and detailed structural description to better understand the formation of solids.