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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, FTIR and MAS 27Al NMR. The results are: 1) the gel shows obvious XRD diffraction peaks, which are different from common Algels 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 AlO 4 Al 12 (OH) 24 (C2O4) 7/2.