Solid-State NMR Spectroscopy of Anionic Framework Aluminophosphates:  A New Method to Determine the Al/P Ratio.

A series of anionic framework aluminophosphates, with different Al/P ratios, have been investigated by various solid-state NMR techniques, including 27Al, 31P magic angle spinning (MAS), 27Al → 31P cross polarization (CP), 27Al{31P} rotational echo double resonance (REDOR), and 31P{27Al} transfer of population double resonance (TRAPDOR). Different Al coordinations (AlO6 , AlO7 , and AlO6b) and P coordinations (PO6 , PO1 Ot, PO2bO06, and PObO16), where b represents bridging oxygens and t represents terminal oxygens, can be unambiguously determined based on the solid-state NMR spectroscopy. Furthermore, a new method to determine the Al/P ratio of open-framework aluminophosphates has been established, which is useful for the understanding of unknown aluminophosphate structures. [ABSTRACT FROM AUTHOR]