Through-bond and through-space connectivities of amorphous aluminophosphate by two-dimensional 27Al-31P heteronuclear NMR

The connectivities between Al and P through chemical bond and internuclear distance have been studied for an amorphous aluminophosphate (a-AlPO4) using two-dimensional (2D) solid-state 27Al-31P correlation NMR (MAS J-HMQC and CP HETCOR). Whereas the conventional 31P MAS spectrum provides less informative results because of poor resolution caused by large distributions of the nucleus surroundings, the 2D HETCOR shows much better resolution and at least four non-equivalent P sites in the a-AlPO4. These P sites are found to be correlated with one [4]Al, two [5]Al and one [6]Al species, and have different chemical shifts. This result might indicate that the mean P-O-[n]Al (n = 4, 5, 6) bond angles are different each other, and they are estimated using the relationship with the 31P chemical shifts in crystalline AlPO4 previously reported.