Open-framework Aluminophosphates Research Articles

Mixed-bonded open-framework aluminophosphates and related layered materials

The structural features, the synthesis and the role of templates in the synthesis for mixed-bonded open-framework aluminophosphates and related layered materials will be reviewed in this article. These aluminophosphate materials differ from the (4,2)-connected aluminophosphates and zeolites in that they contain TO5 and/or TO6 primary building units or terminal T-O bonds (T stands for Al or P). The extra ligands for the TO5 and TO6 units in the aluminophosphates with framework Al/P = 1 are either bridging OH groups or H2O molecules in most cases whereas the terminal T-O bonds are either P-OH or P=O species with P=O bonds being prevalent in layered aluminophosphates. Most of TO5 or TO6 containing aluminophosphates are prepared using a cyclic amine or a diamine as the structure directing agent (template), and the aluminophosphates with Al/P<1 or the layered materials tend to form from an alcoholic medium. Both synthetic conditions and templates play a critical role in determining the composition and structural feature of these materials.

Aluminophosphate Chain-to-Layer Transformation

The synthesis and characterization of two novel aluminophosphate materials, obtained from the same nonaqueous tetraethylene glycol−cyclopentylamine system, is reported. The first material, [Al3P5O20H]5-·5[C5H9NH3+], denoted UT-2, has a 1-D chain structure with a P:Al ratio of 5:3, rather than 1:1 as found in the aluminophosphate AlPO4-n molecular sieves. The UT-2 chains are hydrogen-bonded together by terminal phosphate groups and organized into a layered structure. The second material, [Al2P3O12H]2-·2[C5H9NH3+], denoted UT-3, has a 2-D layer structure with a P:Al ratio of 3:2. Both materials have bilayers of charge-balancing cyclopentylammonium cations interdisposed between anionic aluminophosphate sheets. Variable-temperature in situ PXRD establishes a clean solid-state structural transformation, at 200 °C, of UT-2 to UT-3. The discovery of this chain-to-layer conversion suggests a new paradigm for the templated assembly of 1-D chain, 2-D layer, and 3-D open-framework aluminophosphates.