Characterization of microporous aluminophosphate IST-1 using 1H Lee–Goldburg techniques

Abstract

The presence of two independent methylamine species in microporous aluminophosphate IST-1 (|(CH 3NH 2) 4(CH 3NH + 3) 4(OH −) 4|[Al 12P 12O 48]) has been shown previously by synchrotron powder X-ray diffraction. One of these species, [N(1)–C(1)], links to a six-coordinated framework Al-atom [Al (1)], while the other methylamine [N(2)–C(2)] is protonated and hydrogen-bonded to three O-atoms [O (1), O (2) and O (12)]. We revisit the structure of IST-1 and report the complete assignment of the 1H NMR spectra by combining X-ray data and high-resolution heteronuclear/homonuclear solid-state NMR techniques based on frequency-switched Lee–Goldburg homonuclear decoupling and 31P– 31P homonuclear recoupling. Careful analysis of the 2D 1H–X homonuclear correlation (X = 1H) and 2D heteronuclear correlation (X = 13C, 31P and 27Al) spectra allowed the distinction of both methylamine species and the assignment of all 31P and 13C resonances. For the first time at a relatively high (9.4 T) magnetic field, symmetric doublet patterns have been observed in the 13C spectra, caused by the influence of the 14N second-order quadrupolar interaction.