Purification of aluminum tridecamer salt using organic solvent precipitation

Aluminum tridecamer (Al13) salt of 70% purity can be yielded by slowly adding base to a mixed aluminum chloride solution with sodium chloride as the primary byproduct. The purity of the so-produced Al13 solution is typically increased to >90% using sulfate precipitation and nitrate metathesis reactions (the SO42−/Ba2+ separation method). However, the presence of excess sulfate and, as demonstrated in this study, excess chloride ions can destabilize Al13 clusters. This study applied the organic solvent precipitation technique to purify crude Al13 salt. The solution and solid-state 27Al nuclear magnetic resonance (NMR) spectra indicate that Al13 purity was >95%. The infrared adsorption spectra had clear Al13 characteristic bands. The electrospray ionization mass spectrometry (ESI-MS) tests identified Al137+ species. The organic solvent precipitation method purified Al13 clusters with minimal free Cl− ions.

Graphical abstractBase titration curves for purified Al13 solutions with or without dosed NaCl.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ Organic solvent precipitation method purified Al13 powders. ▶ Organic solvent precipitation method prevents use of sulfate ions. ▶ Organic solvent precipitation method retains minimal quantity of Cl−. ▶ Excess Cl− ions may destabilize Al13 salts.