Synthesis and characterization of Al_(13)-oxalate gel with Keggin structure

In this study, the Al13-oxalate gel synthesized from Al13 solution was characterized by XRD, FTIR and MAS 27Al NMR. The results are: 1) the gel shows obvious XRD diffraction peaks, which is different from common Al gels and their oxalate precipitations; 2) the peak of Al-O stretch vibration of Al13-oxalate complexes at 810 cm-1 indicates that the gel was formed directly by the complexes, and the characteristic peaks of IR and solid-state NMR respectively occur at 725 cm-1 and ～6.1×10-5 chemical shift, which are respectively assigned to (Al-O)Td vibration and (Al-O)4 tetrahedron, suggesting that the gel has a unique Keggin structure; 3) Al13 polyoxocation can directly form gel with oxalate, even in a high-pH environment (=7.8). This finding provides new evidence for the universality of Al13 in natural environments. Through chemical analysis, the chemical formula of the gel was determined to be AlO4Al12(OH)24(H2O)12(C2O4)7/2.

In this study, the Al13-oxalate gel synthesized from Al13 solution was characterized by XRD, PTIR and MAS 27A1 NMR. The results are： 1） the gel shows obvious XRD diffraction peaks, which is different from common AI gels and their oxalate precipitations; 2） the peak of A1-O stretch vibration of Al13-Oxalate complexes at 810 cm^-1 indicates that the gel was formed directly by the complexes, and the characteristic peaks of IR and solid-state NMR respectively occur at 725 cm^-1 and -6.1×10^-5 chemical shift, which are respectively assigned to （AI-O）Td vibration and （A1-O）4 tetrahedron, suggesting that the gel has a unique Keggin structure; 3） Al13 polyoxocation can directly form gel with oxalate, even in a high-pH environment （=7.8）. This finding provides new evidence for the universality of Al13 in natural environments. Through chemical analysis, the chemical formula of the gel was determined to be AlO4Al12（OH）24（H2O）12（C2O4）7/2,