S. Oliver et al., SYNTHESIS AND CHARACTERIZATION OF A FLUORINATED ANIONIC ALUMINOPHOSPHATE FRAMEWORK UT-6, AND ITS HIGH-TEMPERATURE DEHYDROFLUORINATION TO ALPO4-CHA, Journal of materials chemistry, 7(5), 1997, pp. 807-812
The structure of an anionic aluminophosphate molecular sieve UT-6 has
been determined by single-crystal X-ray diffraction and F-19 MAS NMR,
P-31 CP MAS NMR and Al-27 MQ MAS spectroscopy. Large crystals were gro
wn in a non-aqueous synthesis system when hydrogen fluoride was used i
n trace amounts. The title compound, [Al3P3O12F](-)[C5H5NH](+).0.15H(2
)O, crystallizes in the triclinic space group <P(1)over bar> (no. 2),
with Z = 2, a = 9.118(1), b = 9.161(1), c = 9.335(1) Angstrom, alpha =
85.98(1), beta = 77.45(1), gamma = 89.01(1)degrees, V = 759.25(14) An
gstrom(3), R-1 = 0.0280 and wR(2) = 0.0830. UT-6 is a small pore mater
ial that has a three-dimensional network of channels running through t
he structure. The structure is closely related to that of chabazite. I
n addition to alternating tetrahedral phosphorus and aluminium atoms c
onnected by bridging oxygens, there are also isolated pairs of octahed
ral aluminiums in the four-membered rings of the UT-6 framework that s
hare two bridging fluorine atoms. The resulting negative charge on the
framework is balanced by pyridinium cations that reside in the chabaz
ite cages. Upon thermal treatment of UT-6, pyridine molecules and HF a
re removed from the structure and the material transforms into rhomboh
edral AlPO4-CHA, as evidenced by in situ high-temperature powder X-ray
diffraction, thermogravimetry and mass spectrometry. This represents
the first solid-state transformation of an anionic aluminophosphate mo
lecular sieve framework to an entirely neutral one.