Investigation on the Chain-to-Chain and Chain-to-Open-Framework Transformations of Two One-Dimensional Aluminophosphate Chains

Using ethylenediamine as a template, two one-dimensional (1-D) aluminophosphate compounds [AlP2O8H][NH3CH2CH2NH3] (1) and [AlP2O8][NH3CH2CH2NH3][NH4] (2) have been prepared from a gel system: 1.0:x:y:44 Al(i-PrO)3-H3PO4-en-EG (x = 3.0-9.0, y = 1.011.0). Compound 1 consists of edge-sharing four-membered ring (MR) chains, denoted as AlPO-ESC, and compound 2 consists of corner-sharing 4-MR chains, denoted as AlPO-CSC. The molar ratio of en:H3PO4 in the starting gel has an important influence on the final product. If en:H3PO4 >=1, AlPO-CSC is obtained, while if en:H3PO4 < 1, AlPO-ESC is formed. These two chains can transform to each other upon addition of some extra amount of en or H3PO4 to the reaction mixture in which AlPO-ESC or AlPO-CSC is crystallized. On the basis of XRD and 27Al and 31P MAS NMR analyses, a possible chain-to-chain transformation mechanism is proposed. The corner-sharing 4-MR chains of AlPO-CSC, as well as the edge-sharing 4-MR chains of AlPO-ESC can be assembled to 3-D openframework compound NiAlP2O8·C2N2H9 through Ni2+ cations. It is noted that AlPO-CSC remains in the structure of NiAlP2O8·C2N2H9. It is believed that AlPO-ESC might be first transformed to AlPO-CSC followed by the assembly to 3-D open-framework of NiAlP2O8· C2N2H9 through Ni2+ cations.