SYNTHESIS AND CHARACTERIZATION OF A FLUORINATED ANIONIC ALUMINOPHOSPHATE FRAMEWORK UT-6, AND ITS HIGH-TEMPERATURE DEHYDROFLUORINATION TO ALPO4-CHA

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.