Gallophosphates structure

Many gallophosphate molecular sieves are unstable to calcination in air or in the presence of moisture, which limits the utility of these materials because at room temperature (RT) the templates stuff the channels thus limiting access to the porosity. The ULM-16 structure is interesting because it is stable to 800°C under argon and up to 350-400°C in the presence of oxygen. This stability may reflect the fully connected framework of ULM-16. 

The structure of Cloverite (IZA structure code, CLO) has limited thermal stability in air, which is not surprising for gallophosphates. It has been shown that Cloverite is stable in ambient air or a vacuum up to 500°C, but if the molecular sieve is cooled below 100°C, the structure collapses (153). If the calcined Cloverite is immediately placed in hydrocarbon solvents it can be stored at RT for several months. 

In 19851 a gallophosphate with a porous framework structure was reported by Parise (ref. 4). This was followed by the systematic synthesis of the GaPO family (refs. 5,6) in our laboratory and the structural characterization of several single crystals of the compounds (refs. 7 11). 

Recently, we also focused attention on the synthesis of aluminoarsenates and galloarsenates with open framework structures (refs. 12—14). While the aluminophosphates are labeled as AlPO s, the gallophosphates, aluminoarsenates and galloarsenates can be designated as AlPO s, AlAsO s and GaAsO s respectively. 

FIGURE 7.25 The framework of the synthetic gallophosphate, cloverite, represented as shaded spheres of van der Waals radii. (From C.R.A. Catlow (ed.) (1992) Modelling of Structure and Reactivity in Zeolites, Academic... 

The first breakthrough was provided by Flanigen et al. [7] who, playing on the similarity 2 Si4+ -o-A13+ -f P5+, synthesized microporous aluminophosphates (hereafter noted AlPOs) with structures related to those of zeolites. The structural studies [8] showed however a striking difference between the two families. As already mentioned, the framework of zeolites is built up exclusively from connected tetrahedra which can accept small amounts (<10% of substitution) of other metals, whereas in aluminophosphates and homologous gallophosphates, Al and Ga polyhedra can adopt five and sixfold coordinations, which change [9] the connectivity of the framework, and therefore the shape of the windows. 

The alumino and gallophosphates were formed [7] in the systems amine-Al(Ga)203—P205—H20 using the same way of the synthesis and the same range of temperatures and pressure. However, the introduction of phosphoric acid in the synthesis lowered the pH of the solutions to a neutral or weakly acidic medium which favours higher coordinations for aluminium and gallium ions. The combined effect of pH and of the shape of the amines lead to ca two hundred structure types. 

According to Maggard and Boyle [26], the charge densities of layered vanadate units [VxOy] vary from -0.0362 to -0.0493 ek. The charge density of the gallophosphate layer in the structure of MIL-35,... 

T. Loiseau and G. Ferey, Oxyfluorinated Microporous Compounds, VII. Synthesis and Crystal Structure of ULM-5, a New Fluorinated Gallophosphate Ga1g(P04)14 (HP04)2 (OH)2F7 [ I I3N(CI I2)6NI I3 4 6I I20 with 16-Membered Rings and both Bonding and Encapsulated F. J. Solid State Chem., 1994, 111, 403 415. 

S. Feng and R. Xu, Studies on the Syntheses and Structures of a Novel Family of Microporous Gallophosphates. Chem. J. Chin. Univ., 1987, 8, 867-868. 

Figure 5.32 Structures ofmicroporous gallophosphate built from the SBU oft5 Reproduced with permission from [47], Copyright (2002) American Chemical Society...

C.M. Draznieks, S. Girard, and G. Ferey, Novel Inorganic Frameworks constructed from Double-four-ring (D4R) Units Computational Design, Structures, and Lattice Energies of Silicate, Aluminophosphate, and Gallophosphate Candidates. J. Am. Chem. Soc., 2002, 124, 15326-15335. 

The discovery of aluminum phosphate molecular sieves has fueled the search for new sieve like materials. This search has been amply rewarded. Newsom and Vaughan [13] were able to prepare new gallosilicate phases and gallophosphates have also been prepared [14]. One of the most interesting and startling discoveries is that of zincophosphate and beryllophosphate molecular sieves [15]. They can be prepared under very mild conditions [16] and have structures which closely resemble those of aluminosilicate zeolites [16-17]. These compounds have frameworks [(Zn02)(P02)] which are isoelectronic with the aluminosilicate framework... 

Two ammonium templated gallophosphates Synthesis and structure determination from powder diffraction data of 2D and 3D-GAPON". Micro. Meso. Materials, 2002, 53, 87. 

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