Phosphate, inorganic structures

In our studies of the open-framework zinc oxalates, we have recently isolated monomeric, dimeric, ID linear chain, 2D layer, and 3D structures by the reaction of amine oxalates with Zn2+ ions,21 suggesting thereby that the presence of a hierarchy of structures is not unique to the phosphates alone. We believe that the evidence provided by our studies for the existence of an Aufbau principle of open-framework complex structures is of considerable significance. Many other complex inorganic structures are also likely to be formed by similar building-up processes, involving basic building units and self-assembly. 

Zeolites and related aluminosilicates constitute a vital family of microporous materials with immense applications in catalysis, sorption and separation processes [1-3]. The discovery of aluminophosphates is an important landmark in the science of these materials [4], All these materials are, in general, synthesized under hydrothermal conditions by making use of template molecules [2]. The template molecules are usually organic amines and they are involved in the formation of these framework structures in more ways than one. While it is difficult to pinpoint the exact manner in which the amines participate or direct the formation of these inorganic structures, it is generally believed that their size and shape are crucial in determining the pore structure. In recent years, a variety of open-framework structures formed by divalent metal phosphates... 

This chapter presents an overview of the crystal structures of inorganic compounds in which actinide polyhedra are directly coordinated by phosphate or arsenate tetrahedra. Arsenates are considered here for comparative purposes, because of the very similar structural roles played by arsenate and phosphate ions. Structural data are taken mainly from the Inorganic Crystal Stmcture Database [6] and the published literature. Entries from the Powder Dififtaction File of the International Centre for Diffraction Data [7] have been consulted in the case of compounds whose structures may reasonably be inferred. Mixed organic-inorganic compounds [8] and polyoxometalates are not addressed phosphites, phosphinates and arsenites also fall outside the scope of this chapter. Data are tabulated for a given structure type, with phosphates separated... 

A remarkable stereospecificity between the chiral templates and the chiral inorganic structural motifs is illustrated in open-framework zinc phosphate [Con(en)3] [Zn4(H2 P04)3(HP04)2(P04)(H20)2] (JLU-9).[90] It crystallizes in the orthorhombic space group Pbcn with a = 10.4787(8) A, b = 20.0091(14) A, and c= 14.9594(10) A. The asymmetric unit, as shown in Figure 7.52, contains two unique Zn atoms and four unique P atoms. Both Zn(l) and Zn(2) are tetrahedrally coordinated, making four Zn—O—P... 

N. Peres, A. Boukhris, M. Souhassou, G. Gavoille and C. Lecomte, Electron density in ammonium dihydrogen phosphate non-uniqueness of the multipolar model in simple inorganic structures, Acta Cryst. ASS, 1038-1048 (1999). 

Significant catalytic activity has been reported for many inorganic phosphate salts, including those of B, Al, Fe, Cr, Cu, Zn, Cd, Hg, V, Bi, Mo and Zr As with other catalysts, their activity is dependent upon surface area and pore volume, and is often improved by slight non-stoichiometry. Some prescribed phosphate catalysts are not too well-defined mixtures and their preparation should always follow the given recipe. These considerations have stimulated the investigation of many of the newer complex phosphate cavity structures (Chapter 5.7) as possible catalysts [17],... 

For the size exclusion chromatography of proteins on silica-hased diol packings, it is generally recommended to use fully aqueous mobile phases with a salt concentration between 0.1 and 0.3 M. In general, a phosphate buffer around pH 7 is used as the mobile phase. Under these circumstances, the tertiary structure of most proteins is preserved without difficulty and the interaction of proteins with each other is minimized. However, other inorganic buffers or combinations of buffers with organic solvents can be used without difficulties for special applications. 

Some microbial exopolysaccharides contain the inorganic substituents phosphate and sulphate. Phosphate has been found in exopolysaccharide from bacteria of medical importance, including Escherichia coli. Sulphate is far less common than phosphate and has only been found in spedes of cyanobaderia. In addition to these inorganic components, which form part of the structure of some exopolysaccharides, all polyanionic polymers will bind a mixture of cations. Exopolysaccharides are, therefore, purified in the salt form. The strength of binding of the various cations depend on the exopolysaccharide some bind the divalent cations calrium, barium and strontium very strongly, whereas others prefer certain monovalent cations, eg Na ... 

The analysis of phosphates and phosphonates is a considerably complex task due to the great variety of possible molecular structures. Phosphorus-containing anionics are nearly always available as mixtures dependent on the kind of synthesis carried out. For analytical separation the total amount of phosphorus in the molecule has to be ascertained. Thus, the organic and inorganic phosphorus is transformed to orthophosphoric acid by oxidation. The fusion of the substance is performed by the addition of 2 ml of concentrated sulfuric acid to — 100 mg of the substance. The black residue is then oxidized by a mixture of nitric acid and perchloric acid. The resulting orthophosphate can be determined at 8000 K by atom emission spectroscopy. The thermally excited phosphorus atoms emit a characteristic line at a wavelength of 178.23 nm. The extensity of the radiation is used for quantitative determination of the phosphorus content. 

For microporous compounds with special compositions, calcination effects are even more severe. As compared with zeolites, these compounds have lower thermal stability. Strictly speaking, most of them are nonporous since removal of the occluded guest molecules by calcination usually results in collapse. This is due to strong H-bonds with the framework, coordination bonds, and sometimes the templating molecule is shared with the inorganic polyhedra. Relevant examples of low-stability microporous compounds with interesting structural features are zeolitic open-framework phosphates made of Ga [178], In [179], Zn [180], Fe [181],... 

Ray, N. H. (1979). The structure and properties of inorganic polymeric phosphates. British Polymer Journal, 11, 163-77. 

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