Synthetic inorganic ion-exchangers-I Hydrous oxides and acidic salts of multivalent metals.

Layered and pillared metal(IV) phosphates and phosphonates

Metal Phosphonate Chemistry

Phosphonic acids are more acidic than carboxylic acids. They are non-planar and possess twice the number of protons. These attributes lead to strong hydrogen bond formation that can be utilized in design of crystal-engineered structures and self-assembled supramolecular arrays. Their superior cation complexing ability leads to formation of a vast number of metal complexes and their use in lanthanide and actinide separations. Recent work, largely drawn from the work of the author’s research group, is summarized in this update of the author’s 1996 review [Curr Opin Solid State Mater Sci 1 (1996) 268].

Recent advances in metal phosphonate chemistry II

Properties of both amorphous and crystalline salts of tetravalent metals are reviewed, with special emphasis on the much studied salt of zirconium phosphate. The discussion includes: (1) method of preparation, (2) interlayered crystal structure, (3) effect of counter ions on interlayer distance and steric hindrance, (4) mechanism of ion exchange, and (5) the interaction of polar molecules. Other insoluble acid salts with a layered structure include the phosphates of titanium, hafnium, germanium, tin, lead, and the arsenates of titanium, zirconium, and tin. Fibrous precipitates of the insoluble acid salts of cesium and thorium phosphate are mentioned briefly. Under appropriate experimental conditions, insoluble acid of unknown structure can be obtained. Investigations of their crystalline structure may be highly desirable. The ion exchange capacities of many of these substances are evaluated. 80 references, 3 tables, 4 figures.

James A. Stynes

Papers

New crystalline phases of zirconium phosphate possessing ion-exchange properties