Zinc phosphates structure

Figure 7.18. Various open-framework zinc phosphate structures formed from a single amine, TETA, by the variation of the synthetic conditions (Choudhury el al. [32]).

Very interesting novel zinc phosphate structures were discovered in the group of Yu and Xu [12] using a combinatorial approach. The setup resembles the one initially described by Akporiaye [5] in that the well are formed in a Teflon block, with each well having a volume of about 800 pi. Product analysis was done with an automated powder XRD setup after the samples had been transferred to a sample holder. Solids were formed from zinc solution, phosphoric acid and N,N -dimelhylpiperazine as precursors. The most interesting material formed was a zinc phosphate with 16-membered ring channels in one direction, but two other structures with smaller pore openings were also described in this publication. 

Zinc phosphate networks based on Zn04 and PO4 tetrahedra display a large structural diversity, and there have been reports of zincophosphate... 

Cartz, L., Servais, G. E. Rossi, F. (1972). Surface structure of zinc phosphate dental cements. Journal of Dental Research, 51, 1668-71. 

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... 

An open-framework zinc phosphate synthesized under mild hydrothermal conditions possesses two interpenetrating helical channels.414 Piperazine phosphate yields a variety of open framework structures in reaction with zinc, including linear chain, layer, and three-dimensional systems.415... 

A zinc phosphate material formed in the presence of traro-l,2-diaminocyclohexane forms with pores of 24-membered rings and a consequent large amount of free space in the structure, Zn3(P04)2(P03OH)(diaminocyclohexane)-2H20. The tubular channels formed... 

Figure 25 Molecular configuration of zinc phosphates, (a) The structure of the system before compression, (b) The structure of the system when compressed to 16 GPa. (c) The structure of the system when fully decompressed. Adapted from Ref. 83.

This is an allosteric enzyme that requires zinc for structural stability. It catalyzes the condensation of carbamyl phosphate with L-aspartate to give carbamyl-L-aspartate and phosphate (equation... 

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. 

FIGURE 6. 3D zinc phosphates with eight-membered rings obtained from the transformation of the ladder compound 2 (a) [C Halos-[Zn2(P04)2] (8) and (b) [C2N2H1o](Zn2(P04)2] (9). The features of the ladder structure can be dearly seen in the 3D strudure of 9. Such features are also present in 4 and 8. 

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 10. Monomeric zinc phosphate, 17, which transforms to the 3D structure, 18, and the tubular layer structure, 19. 

Chidambaram, D. Neeraj, S. Natarajan, S, Rao, C. N. R. Open-framework zinc phosphates synthesized in the presence of structure-directing organic amines, J, Solid State Chem, 1999, 147, 154. Ayyappan, S, Bu, X, Cheatham, A. K, Natarajan, S. Rao, C, N, R. A simple ladder-tin phosphate and its layered relative, Chem, Commun, 1998,218. 

FIGURE 4. Transformations of a zero-dimensional monomeric zinc phosphate to 1D (ladder), 2D (layer), and 3D structures. 

FIGURE 5. Transformation of a four-membered ring zinc phosphate (SBU) to a linear chain phosphate and the transformation of the latter to a 3D sodalite-related structure with a 4688 cage. 

The discussion in the previous sections should suffice to indicate the importance of the transformations of molecular compounds to materials. Studies of such transformations are only making a beginning, and there appears to be a great future for such investigations, Thus, the recent synthesis of a sodalite-related structure from a molecular zinc phosphate is noteworthy, besides the transformation of the centrosymmetric, tetrameric, molecular alumino-phosphate to open-framework structures. Preliminary investigations53 have shown that interesting transformations also occur in metal carboxylates. Thus, molecular zinc oxalate monomers and dimers are found to transform to chain or three-dimensional structures on heating with piperazine in an aqueous medium, The chain structure transforms to a layer structure, We believe that it would... 

Ayi, A, A, Choudhury. A. Natarajan, S, Neeraj, S, Rao. C, N, R, Transformations of Low-Dimensional Zinc Phosphates to complex Open-Framework Structures, Part 1 Zero-dimensional to One-, Two- and Three-Dimensional Structures, J. Mater, Chem, 2001, 77, 11 Bl —119l. 

Dan. M, Udayakumar. D, Rao, C. N, R, Transformation of a 4-membered Ring Zinc Phosphate SBU to a Sodalite-Related 3-Dimensional Structure through a Linear Chain Structure. Chem. Commun. 2003. 2212-2213. 

The one-dimensional framework solids constitute a very small fraction of the gamut of structures known in phosphate-based materials. The existence of one-dimensional structures, however, has been known for some time in the case of aluminum, gallium and zinc phosphates [13-16]. The structures consist of polymeric chains of [MP208]" units supported by the structure-directing... 

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