Structure and properties of the aluminum borates Al(BO2)n and Al(BO2)n, (n = 1–4)



The geometrical and electronic structures of Al(BO2)n and Al(BO2)n (n = 1–4) clusters are computed at different levels of theory including density functional theory (DFT), hybrid DFT, double-hybrid DFT, and second-order perturbation theory. All aluminum borates are found to be quite stable toward the BO2 and BO2 loss in the neutral and anion series, respectively. Al(BO2)4 belongs to the class of hyperhalogens composed of smaller superhalogens, and should possess a large adiabatic electron affinity (EAad) larger than that of its superhalogen building block BO2. Indeed, the aluminum tetraborate possesses the EAad of 5.6 eV, which, however, is smaller than the EAad of 7.8 eV of the AlF4 supehalogen despite BO2 is more electronegative than F. The EAad decrease in Al(BO2)4 is due to the higher thermodynamic stability of Al(BO2)4 compared to that of AlF4. Because of its high EA and thermodynamic stability, Al(BO2)4 should be capable of forming salts with electropositive counter ions. We optimized KAl(BO2)4 as corresponding to a unit cell of a hypothetical KAl(BO2)4 salt and found that specific energy and energy density of such a salt are competitive with those of trinitrotoluol (TNT). © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012