Electrolytic synthesis of aqueous aluminum nanoclusters and in situ characterization by femtosecond Raman spectroscopy and computations

The selective synthesis and in situ characterization of aqueous Al-containing clusters is a long-standing challenge. We report a newly developed integrated platform that combines (i) a selective, atom-economical, step-economical, scalable synthesis of Al-containing nanoclusters in water via precision electrolysis with strict pH control and (ii) an improved femtosecond stimulated Raman spectroscopic method covering a broad spectral range of ca. 350-1,400 cm(-1) with high sensitivity, aided by ab initio computations, to elucidate Al aqueous cluster structures and formation mechanisms in real time. Using this platform, a unique view of flat [Al-13(mu(3)-OH)(6)(mu(2)-OH)(18)(H2O)(24)](NO3)(15) nanocluster formation is observed in water, in which three distinct reaction stages are identified. The initial stage involves the formation of an [Al-7(mu(3)-OH)(6)(mu(2)-OH)(6)(H2O)(12)](9+) cluster core as an important intermediate toward the flat Al-13 aqueous cluster.