Preparation and structure of a gallium phosphate framework with clathrated isopropylamine
1986; Wiley; Volume: 42; Issue: 2 Linguagem: Inglês
10.1107/s0108270186096993
ISSN1600-5759
Autores Tópico(s)Mesoporous Materials and Catalysis
ResumoTrigallium tris(orthophosphate) hydrate-isopropylamine, GaPO4-21, Ga3(PO4)3.C3HgN.H20, M r =571.2 , monoclinic, P2m/n, a = 8 . 7 0 0 ( 1 ) , b = 18-146(2), c = 9 . 0 8 7 ( 1 ) A , f l=107.28 (2) °, IT= 1369.8/~3, Z = 4 , D x = 2 . 7 7 g c m -3, MoKa, 2= 0.7107/~,, /~= 62.0 cm -~, F(000) = 1112, room temperature, atoms in the framework refined anisotropically to R = 0 . 0 4 7 for 2385 reflexions with I > 2a(I). The structure is essentially as described for the aluminophosphate molecular-sieve precursor, A1PO4-21, with the exception of the position of the attempted template isopropylamine, which is statistically disordered over two sites within the pores of the structure. The framework is formed by cross linking corrugated sheets composed of ribbons of edge-shared threeand five-membered rings containing five-coordinated gallium polyhedra and phosphorus-centred tetrahedra, with crankshaft-shaped chains of alternating GaO 4 and PO 4 tetrahedra. Upon calcination, loss of the hydroxyl group, which forms the bridge between threeand five-membered rings, converts GaPO4-21 to the open-framework structure of GaPOc25. Introduction. The synthesis of gallium phosphate frameworks, some of which are related to the series of aluminophosphate compounds reported by workers at Union Carbide Corporation (Wilson, Lok & Flanigen, 1982; Wilson, Lok, Messina, Cannan & Flanigen, 1982) has recently been described (Parise, 1985). This process typically involves the hydrothermal treatment of a galliophosphate gel, to which an amine has been added in an attempt to direct the synthesis towards a particular structure type. Although the exact role of this agent is still in doubt, its presence and aspect in several A1PO4 compounds studied to date (Parise, 1984a,b,c; Parise & Day, 1985; Parise, 1985) suggest the molecule behaves as a template, its shape dictating the geometry of the framework. The observation that only dense phases form in the absence of amines indicates they may play a crucial role in controlling the gel chemistry, nucleation, crystal growth or a combination of these processes. During the investigation of the synthesis of * Present address: The Department of Chemistry, New South Wales Institute of Technology, Broadway, Sydney, NSW 2006, Australia. framework structures in the GaPO 4 system, several new compounds were produced (Parise, 1985). From a comparison of Guinier X-ray powder photographs with published data (Wilson, Lok & Flanigen, 1982), some of these were found to be structurally related to the AIPO 4 family of molecular sieves. One such compound, designated GaPO4-21, is related to A1PO4-21 (Parise, 1984c; Parise & Day, 1985; Bennett, Cohen, Artioli, Pluth & Smith, 1985), the precursor that, upon calcination at above 823 K, is converted into the molecular sieve AIPO4-25 (Wilson, Lok & Flanigen, 1982) with an estimated port size of between 3.4 and 4 .3A. Although the composition of the framework for these compounds is not necessarily AIPO 4 or GaPO4 (see below), it appears as such in the patent literature and will also be used as a forename in designating new frameworks in this and future reports. For example, in GaPO4-21, 'GaPO 4' denotes the approximate composition of the framework while '21' denotes the unique
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