Cloverite structure

The synthesis of Cloverite is also unique in that it established the utility of HF in zeolite molecular synthesis. In the case of silicates, either hydroxide or HF serve to mineralize the silica. That is not needed in the GaP04 synthesis but the F ion plays an important role in stabilizing the structure. The fluoride ion becomes encapsulated in the D4R units. It has been suggested that fluoride ions in fact direct... 

Figure 25. Structure of Cloverite viewed along the 100 direction.

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. 

The only aluminophosphate known having a 20-MR system is JDF-20 (162, 163). The structure of JDF-20 viewed along the 001 direction is shown in Fig. 27. The large 20-MR elliptical channels are 14.5 x 7.9 x 6.2 A in diameter. Like Cloverite, JDF-20 is an interrupted framework that is reflected in the formula [Al5P6024H][N(Et3)H]2.2Fl20, where there is less A1 than P. This results in four P=0 and two O-H-O groups that protrude into the pore window. There are also intersecting channels defined by 10- and 8-MR structures. 

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 most obvious approach to obtain controlled mesoporosity is the extension of zeolite-like three-dimensional framework structures to larger pore-sizes. Zeolite-like compounds in the micro- and mesoporous range are the aluminophosphate VPI-5, cloverite and ULP (MCM-41). These new materials are characterized by pore diameters between 1.3 nm and 20 nm. 

Fig. 3. Polyhedral representation of cloverite (a), ULM-18 (b), LTA (c) and Mu-2 (d) structures based on F -centered D4R units. Fluorine atoms are black spheres.

There are terminal groups in the frameworks, such as P=0, P-OH, and Al OH, which make the structures less stable than zeolites and aluminophosphate molecular sieves with (4,2) networks. These terminal groups also favor the formation of interrupted frameworks, such as cloverite and JDF-20 ... 

A. Cloverite has an extremely open structure, and its framework density is one of the lowest among the known zeolite structures. 

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