Metalophosphates with mixed-polyhedral framework structures : syntheses and characterization

Three new microporous compounds with octahedral-pentahedral-tetrahedral framework structures (so called OPT materials) with metalophosphate composition were prepared under solvothermal conditions and characterized by X-ray diffraction and Mossbauer spectroscopy. Ironalumino- and irongallophosphates are violet and brown-violet crystals with NH4[Fe 1.15 Al 1.85 P 3 O 12 ](H 2 O) 2 and NH4[Fe 1.05 Ga 1.95 P3O 12 ] (H 2 O) 2 composition. Nickel-gallophosphate NH 4 [Ni 1.0 Ga 2.0 P 3 O 12 ](H 2 O) 2 forms light yellow lozenges. All products have isotype crystal structures in space group C2/c. The framework structures are built of comer- and edge-sharing distorted octahedra, trigonal bipyramids and phosphate tetrahedra. Iron occurs in two different valence states and occupies different polyhedra types in the structures, confirmed by Mossbauer spectroscopy. The compounds have three-dimensional channel systems which are filled by ammonium groups and water molecules, forming a strong hydrogen bonding system. Upon heating, the frameworks collapse during deammonization at temperatures below 573 K. A deformation analysis of the different coordination polyhedra in comparable compounds was performed and the structural relationship to a similar ammonium gallophosphate is discussed.