Faujasite atomic coordinates

Table V. Faujasite. Atomic Coordinates of DLS Models with Ordered Si/Al Distributions and Displacements0 (A) from the Symmetrized Positions...

Table IV. Faujasite. Atomic Coordinates of Symmetrized DLS Models...

THE IDEALISED FAUJASITE TOPOLOGY. The following assumptions are made 1) the space group is Fd3m (second setting) and 2) all 192 T atoms are in general positions. The cell dimensions are known and the T-T interatomic distance is assumed to be 3-1A. For convenience the atom coordinates (x,y,z ) are expressed in Angstroms, and not in fractions of the unit cell dimensions. 

Other framework structures based on zeolites have also been synthesized which contain atoms other than aluminium and silicon, such as boron, gallium, germanium, and phosphorus, which are tetrahedrally coordinated by oxygen. Such compounds are known as zeotypes. Pure aluminium phosphate, commonly called ALPO, and its derivatives, can take the same structural forms as some of the zeolites such as sodalite (SOD), faujasite (FAU), and chabazite (CHA) (e.g., ALPO-20 is isostructural... 

CaX and SrX, but it is much more pronounced for nickel faujasite. The Ni(II) occupies two-thirds of the SI sites and attains nearperfect octahedral coordination with six framework oxygens, with all six oxygen atoms shifting. 5 A towards Ni (Fig. 3). The remaining Ni(II) ions are distributed in four unique positions, two in SI sites and the other two in SII and SII sites (Fig. 4). 

The structure of the zeolite faujasite is shown in following figure. In this convention representation the framework structure is shown without depicting, atoms directly. Each line represents an SiOSi or Si O Al connection. Four lines meet at tetrahedral vertices representing the positions of the four-coordinate Si or A1 atoms. Spacefilling models of this zeolite show that the pores can accommodate molecules up to about 750 pm in diameter. 

It was also noted that the stretching vibration frequencies of these groups somewhat increased (by 20-30 cm 1) with increasing content of aluminum in a faujasite lattice (83). From the cluster quantum-chemical viewpoint, this should be attributed to the effects of the aliminum atoms of the second and next coordination spheres of a cluster. 

Other framework structures containing atoms such as aluminium and phosphorus tetrahedrally coordinated by oxygen have been synthesised and are given the generic name zeotypes. Pure aluminium phosphate (commonly known as ALPO) and its derivatives have been found to take the same structural forms as some of the zeolites, such as sodalite and faujasite, as well as some novel structures. The metal-aluminium phosphates can be formed with metals such as Li, Be, Mg, Mn, Fe and Zn replacing some of the aluminium and these are called MeALPOs. If the compound contains silicon or silicon and a metal, partially replacing aluminium or phosphorus leads to SAPOs and MeSAPOs. 

In specific cases, the exact composition of the first coordination sphere around Cu + can be derived from the superhyperfine splitting pattern in ESR. This is illustrated in Fig. 11 for a faujasite-type encagedbisCu(histidine) complex [47]. The axially symmetric ESR spectriun has a hyperfine splitting with values for g, gx and (j of around 2.27,2.06 and 17 mT, respectively and a seven-line superhyperfine structme with an value of 1.23 mT. The additional splitting is due to the presence of three nitrogen atoms (2 nN-tl=7 with and n equal to 1... 

Figure 3.8. (a) Structure of faujasite, with four different O atoms in tetrahedral coordination to Si and Al (b) Br0nsted acid OH groups, bridging between Si and A1 sites. 

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