Layered phosphates

Layered phosphate/phosphonate and phosphonate materials, obtained by substitution of the phosphate moiety by phosphonate groups, display interesting tunable hydrophilic/organophilic properties for adsorption processes. When Candida rugosa lipase (CRL) is simply equilibrated with zirconium phosphate and phosphonate [135,136], immobilization was demonstrated to take place at the surface of the microcrystals. However, because lipase exhibits a strong hydrophobic character, its uptake by zirconium phosphate and phosphonate was much more related to the hydrophobic/hydrophilic character of the supports than to the surface area properties. A higher uptake is observed for zirconium-phenylphosphonate (78 %)... 

The affinity between the tetrahedrally arranged orthophosphate oxyanion, P04, and hexava-lently coordinated metal cations lends itself to a classification of phosphate minerals in a scheme similar to silicates (SiO -) framework, insular, chain, and layer phosphates. Examples of this scheme, advanced by Povarennykh (1972) and further elaborated by Lindsay Vlek (1977), include berlinite (AIPO4 framework) hydroxyapatite (insular) monetite (CaHP04, chain) and vivianite (Fe4(P04)2-2H2O, layer). 

The amount of char formed and its structure are key parameters accounting for the effectiveness of an FR system. The enhancement of the charring activity of IFR systems or OMLS can be enhanced by the use in combination of nanoparticles having a strong catalytic activity for carbonization processes. Some layered phosphates seem promising, since they can also promote the formation of graphitized structures. 

Design of Layered Phosphate Hosts Containing Multiply Bonded Bimetallic Guest Species... 

On the basis of these properties, the three approaches summarized in Figure 3 have been elaborated specifically for the introduction of photoactive M—— M cores into layered phosphate host structures. These are (1) the direct intercalation of solvated M—— M cores into layered phosphates wherein the phosphate groups of the layers form the ligation sphere for the bimetallic core (2) acid-base reaction of specially functionalized ligands on the bimetallic core with protons from the layers and (3) replacement of the phosphate groups with functionalized phosphonates that offer well-defined coordination sites for the M—M core. We now discuss each of these methodologies. 

Figure 3. Three basic strategies for the incorporation of multiply bonded metal-metal guest species into vanadyl and zirconium phosphate host layers, (a) The direct intercalation of solvated M—— M cores into the native layered phosphate host structure, (b) Incorporation of M—— M complexes with ancillary ligands containing a Lewis basic site, (c) Coordination of M—— M cores with ligands provided from modified phosphate layers.

FIGURE 3. (a) One-dimensional ladder phosphate with 1,3-diamino-propane (DAP), I FMIZnJHPO (5), and (b) the two-dimensional layer phosphate, [C3N2HH] [Zn2(HP04)3] (6), obtained by the reaction of Zn2+ ions with 1,3-diaminopropane phosphate (DAPP). We can see the features of a zigzag ladder in 6. 

FIGURE 7. (a) 2D layer phosphate, [C4N2H10] (Zn PC J (10). obtained from the transformation of the ladder compound 2. (b) A 2D layer compound, [C3N2Hi2][Zn4(P04)2(HP04)2] (11), obtained from the transformation of the ladder conpound 5. Both 10and11 exhibit features of the ladder structure, from which they are formed. 

FIGURE 8. Linear chain phosphate, [CnWfaNZntHPQdz] (12), which transforms to a tubular layered phosphate, [C10N4l-y [Zn3(P04)2-(HP04)1 (13). The features of the linear chain can be delineated in the tubular structure of 13. 

We have carried out the reactions of 2D layered zinc phosphates to see whether they transform to 3D structures. Thus, the layer structure [Ct5N4H22]o.5[Zn2(HP04)3] (3), on heating in water at 150 °C (3 H20 = 1 200), gave the 3D structure 4 with 16-membered channels. It must be recalled that we could obtain this 3D structure from the ladder structure, 2, as well. Heating the tubular layer phosphate obtained with TETA, [C6N4H22lo.5[Zn3(P04)2-(HP04)] (14), at 150 °C in water (14 H20 = 1 100), produced the 3D structure, 8. 

FIGURE 9- Layer phosphate, 15, and ladder phosphate, 16, obtained from the transformation of the zero-dimensional monomer, 7. 

FIGURE 8. Transformation of a four-membered ring aluminophos-phate (S4R) to a layered phosphate, which then undergoes transformation to another layered structure by the loss of water molecules, Note that the 2D component contains four-membered... 

Figure 2. Reaction of an organic amine phosphate with Zn(II) ions to give a iadder and a layer phosphate.

Solid phosphates show a huge variety of crystal structures, and it is not practical to classify them in terms of structural types as is done with simple oxides, halides, etc. However, some general classes of metal phosphate structures will be considered three-dimensional frameworks of linked phosphate tetrahedra and tetrahedrally or octahedrally coordinated cations, layered phosphates, and phosphate glasses. In all of these materials the size and topology of pores within the structure are of importance, as these determine the ability of ions and molecules to move within the structure, giving rise to useful ion exchange, ionic condnction, or catalytic properties. Ion exchange can also be nsed to modify the properties of the host network, for example, the nonlinear optical behavior of potassium titanyl phosphate (KTP) derivatives. 

Table 9 Examples of organometallic intercalation compounds formed by the layered phosphates...

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