Metal-halide frameworks, dimensional

Dimensional reduction has been set forth as a general method for dismantling noncluster metal-halide and -chalcogenide frameworks in a controlled, predictive manner (74). In such a reaction, a binary parent compound ML is heated with n equivalents of a dimensional reduction agent AJL, where A is significantly more electropositive than M. 

The donors face to each other to assume a dimeric structure, with close intradimeric S-—S conducts of 3.43-3.52 A. Consistent with the absence of significant interdimeric S—-S interactions, the two compounds exhibit low electric conductivity. The diversity of copper halide frameworks, affected by several elements such as the metal ions, coordination of the halogen atoms, and the stereofactors of the ligand, makes it possible to design two- and three-dimensional coordination polymers. 

Solids with octahedral, tetrahedral, square planar, and linear metal coordination geometries, including many different types of polyhedra connectivity modes, are amenable to dimensional reduction. Tulsky and Long compiled an enormous database of over 300 different allowed combinations of M and X and over 10,000 combinations of A, M, and X. The formalism may be extendable to quaternary phases as well. However, frameworks containing anion-anion linkages, anions other than halides, oxide, or chalcogenides, nonstoichiometric phases, and mixed-valence compounds were excluded from their initial study. 

Solid phosphates show a huge variety of crystal structures, and it is not practical to classify them in terms of structural types as is done with simple oxides, halides, etc. However, some general classes of metal phosphate structures will be considered three-dimensional frameworks of linked phosphate tetrahedra and tetrahedrally or octahedrally coordinated cations, layered phosphates, and phosphate glasses. In all of these materials the size and topology of pores within the structure are of importance, as these determine the ability of ions and molecules to move within the structure, giving rise to useful ion exchange, ionic condnction, or catalytic properties. Ion exchange can also be nsed to modify the properties of the host network, for example, the nonlinear optical behavior of potassium titanyl phosphate (KTP) derivatives. 

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