Unraveling\nthe Structural Evolution of Aluminum Polyoxocations\nin Solution

The primary objective within the\nrealm of aluminum solution\nchemistry\nis to elucidate the structural changes in aluminum polyoxocations\nunder the influence of altered solution conditions. Notably, previous\nreports are primarily focused on specific types, such as aluminum\nmonomers, species from the Keggin series, and the planar Flat-Al<sub>13</sub><sup>15+</sup> (F-Al<sub>13</sub>) cluster. As a result,\nthere is a lack of comprehensive understanding of the remaining aluminum\npolyoxocations and their respective transformation pathways. In response\nto this lack, we adopt a combined experimental and theoretical approach\nto explore the spectral properties of aluminum polyoxocations. Specifically,\nwe analyze infrared spectra, Raman spectra, and aluminum-27 nuclear\nmagnetic resonance (<sup>27</sup>Al NMR) spectra. Notably, the changes\nin the spectral features originate from varying solution basicity\nlevels. Through our findings, we can categorize the Al–O clusters\ninto three primary groups: Al(H<sub>2</sub>O)<sub>6</sub><sup>3+</sup> (Al<sub>1</sub>), ε-Keggin-[AlO<sub>4</sub>Al<sub>12</sub>(OH)<sub>24</sub>(H<sub>2</sub>O)<sub>12</sub>]<sup>7+</sup> (ε-Al<sub>13</sub>), and 6-coordinated aluminum species. Notably, the Raman\nspectra exhibit prominent peak shifts at 559 and 595 cm<sup>–1</sup>, indicating the existence of Al<sub>3</sub>(1) intermediates during\nthe transition from the Al monomer to the ε-Al<sub>13</sub> cluster.\nOverall, this paper presents a comprehensive summary of the possible\nmechanisms that govern the formation of ε-Al<sub>13</sub> from\nAl<sub>3</sub>(1), offering a clearer picture of the aluminum polyoxocation\nlandscape and its dynamics under various solution conditions.