Directing Effect Of Fluoride In The Synthesis Of Molecular Sieves With New Characteristics And Of The First Twenty-Membered Ring Microporous Solid

Abstract

ABSTRACTThe directing effect of fluoride anions in the synthesis of molecular sieves seems to be related to the strength of its interaction with the framework. For example, whereas F is bridging 2 Al atoms of a four-membered ring in AlPO4-5 containing tetrapropylammonium fluoride and in an new triclinic morpholine-containing chabazite-like AlPO4, it is found in double four-rings in three other phases which were synthesized recently. Firstly in the tetragonal all-silica AST-type octadecasil (space group I4/m, a = 9.194(2)Å c = 13.396(4)Å) which was obtained in the presence of quinuclidine and HF. Secondly in two novel cubic microporous gallophosphates which are formed selectively in the presence of hydrofluoric acid. One has the structure type LTA (space group Fm3c, a = 24.0354(1)Å) and crystallizes with di-n-propylamine as a template, and the other shows a novel structure type (space group Fm3c, a = 51.84Å) with a 3-dimensional 20-membered ring channel system. This is the largest membered ring ever reported for a synthetic material.