MetalIV Phosphonates

A fundamental step in the development of the chemistry of layered phosphates was made in 1978

Intercalated crystals (50% loading capacity)

Intercalated crystals (50% loading capacity)

Figure 11 Schematic representation of the exfoliation of a-Zr(HPO4)2• H2O microcrystals by intercalation of n-propylamine. The formation of completely inorganic films or the coating of solid surfaces is also reported.
Figure 12 Schematic representation of a pillared layered structure showing the microporosity and the diffusion paths.

when the first Zr(IV) phosphonates and Zr(IV) organophosphates with formula Zr(RPO3)2 or Zr(ROPO3)2 respectively, were prepared (R being an organic group). These compounds are organic derivatives of a-Zr(HPO4)2 • H2O in which the -OH groups attached to the phosphorous atoms have been replaced by organic R groups, leaving the inorganic structure of the a-layer essentially unchanged.

A further development in layered metal(IV) phosphates was achieved with the resolution of the structure of the y-phases and with the discovery that it is possible to replace interlayer dihydrogenphosphate groups by monovalent phosphonate or phosphinate anions by simple topotactic anion exchange reactions (see above).

Nowadays, a large number of metal(IV) phosphonates of a- and y-type are known and many others can be prepared for special purposes, constituting a very large and versatile class of layered materials. A brief account of preparation procedures, structural

Figure 13 Computer-generated representation of the sequence of two layers of a-Zr(C6H5PO3)2. (Data from Alberti G, Costantino U, Allulli S and Tomassini N (1978) Journal oflnorganic and Nuclear Chemistry 40: 1113-1117, with permission from Elsevier Science.)

features and the chemistry of a- and y-zirconium phosphonates is given.

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