Layered metal phosphate hosts

Structures and Exchange Properties of Layered Metal Phosphate Hosts... 

Group (IV) metal phosphates and phosphonates, transition metal oxides (titanates, silicates, niobates, etc.), layered oxides, and double hydroxides (aluminum, magnesium, iron, etc.) are some of the inorganic compounds used as layered host ma-... 

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.

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. 

In 1995, Morgan et al. synthesized a layered aluminophosphate compound by using a chiral cobaltammine complex as the template for the first time.[61] Recently, the Jilin group has synthesized a number of 2-D layered and 3-D open-framework metal phosphates by using a racemic mixture or an optically pure chiral metal complex as the template, and has systematically studied the chirality transfer from the guest chiral complex templates to the host inorganic open frameworks.1901 Table 7.15 lists some metal phosphates and oxides with open-framework structures templated by optically pure or racemic cobalt ammine complexes. 

Polypyridine complexes of transition metals such as Ru, Fe, Os, Rh and Cr have been under active investigation [1]. Various layered materials such as clay minerals, metal phosphates and transition metal oxides have been known as host materials for intercalation compounds. On this basis, intercalation compounds have been studied as catalysts [2],... 

Intercalation Through Acid-Base Interactions. Such mechanisms are observed in layered host lattices (metal phosphates layered perovskites HCa2Nb30io, HCa2Nb2M09 with M = Al, Fe, HMM Oe H2O with M = Nb,... 

Although there are numerous families of lamellar solids, only a handful of them exhibit the kind of versatile intercalation chemistry that forms the basis of this book. In arriving at the content of this volume, the editors have accurately identified six classes of versatile layered compounds that are at the forefront of materials intercalation chemistry, namely, smectite clays, zirconium phosphates and phos-phonates, layered double hydroxides (known informally as hydrotalcites or anionic clays ), layered manganese oxides, layered metal chalcogenides, and lamellar alkali silicates and silicic acids. Graphite and carbon nanotubes have not been included, in part because this specialty area of intercalation chemistry is limited to one or two molecular layers of comparatively small guest species that are capable of undergoing electron transfCT reactions with the host structure. 

The concepts developed through the pillaring of layered silicate clays and group-IV metal phosphates should be extended to other classes of layered host structures. Some work has been initiated in the area of related layered phosphates (e.g., vanadyl and uranyl phosphates), and this approach should be extended. Layered compounds with well-defined structures should receive first priority because they present the best possibilities for a molecular design approach. 

In addition to the clay-organic systems, dye-intercalated layered solids including zirconium phosphates and transition metal oxides will be discussed (50-51). Due to the variation of layer charge density, particle morphology, and electronic properties, host-guest systems with unique microstructures and properties have been obtained. 

Intercalation of ruthenium poly(pyridine) complexes into other layered materials has been reported (95-106). The intercalation is not as facile as in smectite systems, which is partly due to the higher charge densities of these host materials. Consequently, quantitative ion exchange of ruthenium complexes with the interlayer cations is difficult. Synthetic efforts have been made to introduce ruthenium polypyridine chelate complexes into magadiite, zirconium phosphate and phos-phonates, LDH, MnPSs, and a transition metal oxide and to control the adsorption states. 

Depending on the final purpose of the material, the appropriate pillar can be chosen. This flexibifity in the PILC synthesis is one of the main advantages compared to other porous substrates, such as zeofites, which have one definite pore size. The technique not only focuses on clays, but other layered structures serve as host materials as well. Examples are layered double hydroxides (anionic clays), metal(IV)- phosphates and phosphonates,layered silicic acids, etc. [4,5]. 

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