Phosphates with Layer Structures

In addition to uranium-bearing minerals such as autunite and torbernite, reported uranium salts include 

Autunite, Ca(U02)2(P04)2 H20, n = 6-10, is representative of a class of minerals and synthetic products of the general formula U02P04 H20 which have layer-like structures and which 

If zirconium salt solutions are mixed with orthophosphoric acid at room temperature, aqua gels of zirconium acid phosphates are obtainable with Zr/P = 0.5-2.1. Both amorphous and crystalline varieties with the composition Zr(HP04)2 H20have now been investigated [20,21]. 

What was formerly believed to be the y form of the above zirconium salt was later shown to be more accurately described by the formula ZrP04(H2P04) 2H2O. 

The ion exchange properties of the a-zirconium compound can be used for the separation of some radioactive elements. Full ion exchange capacity is developed at pH 9-10, but the best separations are achieved at pH 3. These include Cs+ from Rb+ and Ra + from Ba +. The cerium salt Ce(HP04)2 riW-f) can be fabricated in fibrous form which is an effective ion exchanger for Sr + (Table 5.31). 

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Spherical particles of various metal phosphate particles can be prepared by precipitation using urea as a homogeneous precipitation agent. Surface-active agents, such as SDS and CTAC, are effective in preparation of uniform-size spherical particles. The formed spherical particles are amorphous and contain OH- and H20, except cobalt phosphate particles with layered structure. These panicles are agglomerates of primary particles, and have pores of different sizes ranging from ultramicropore to mesopore. 

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer structures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer structure with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

The properties of a- or y- zirconium hydrogen phosphate, a synthetic inorganic ion-exchanger material with layered structure, as "heterogenizing" support for carbonylation reactions are still to be studied. Our first studies in this field showed that the Pd(II)-2,2 -bipyridyl complex intercalated in these materials catalyzes the oxidative carbonylation of aniline even though its activity falls with time, because the support slowly loses palladium and deactivates during the catalysis process [2]. 

The presence of triethylenetetramine in the hydrothermal synthesis of open-framework zinc phosphates results in a number of frameworks with one- to three-dimensional structures. The structures include one-dimensional ladders, two-dimensional layer structures, and one structure where the tetramine is bound to the zinc center. The structural type was highly sensitive to the relative concentration of the amine and phosphoric acid.411 Piperazine and 2-methylpiperazine can be used as templating molecules in solvothermal syntheses of zinc phosphates. The crystallization processes of the zinc compounds were investigated by real time in situ measurements of synchrotron X-ray powder diffraction patterns.412... 

A Cameron-Plint friction machine generated tribofilms with two-layer structure a zinc polyphosphate thermal film overlying a mixed short-chain phosphate glass, containing iron sulfide precipitates. A tribochemical reaction between the zinc polyphosphate and the iron oxides species is proposed on the basis of the hard and soft acid and base HSAB principle (Martin, 1999 Martin et al., 2001). 

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 4. X-ray diffraction patterns of the products of the reaction of DAPP with Zn2+ ions, (a) XRD pattern of the monophasic zinc phosphate with a ladder structure, and (b) XRD pattern of the mono-phasic layered zinc phosphate. The diffraction patterns (c)—(f) are those of the products obtained from the reaction of DAPP with Zn2+ ions at different temperatures, as indicated (duration of reaction, 24 h). Notice the presence of reflections due to the ladder and the layer structures in the patterns and the time evolution of phases. The XRD pattern (0, in addition, shows a unique reflection due to an unidentified precursor. The XRD pattern (g) is that of the amine phosphate (DAPP). The inset at the top of the figure shows the formation of the ladder and the layer structures and their time evolution at 150 °C. 

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. 

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