Theoretical study of the stability and electronic structure of Al(BH 4)n=1→4 and Al(BF4)n=1→4 and their hyperhalogen behavior

Using density functional theory (DFT), we have systematically calculated the equilibrium geometries, electronic structure, and electron detachment energies of Al(BH4)n=1&rarr4 and Al(BF4) n=1&rarr4 at the B3LYP/6-311+G(2d,p) level of theory. The electron affinities of Al(BH4)n not only exhibit odd-even alternation, just as seen in (BH4)n, but also, for n = 3 and 4, show a remarkable behavior: whereas the electron affinities of BH 3 and BH4 are, respectively, 0.06 and 3.17 eV, those of Al(BH4)3 and Al(BH4)4 are 0.71 and 5.56 eV. Results where H is replaced by F are also very different. The electron affinities of BF3 and BF4 are, respectively, -0.44 and +6.86 eV, and those of Al(BF4)3 and Al(BF 4)4 are 1.82 and 8.86 eV. The results demonstrate not only marked difference when H is replaced by F but also substantially enhanced electron affinities by almost 2 eV when BH4 and BF4 units are allowed decorate a metal atom, confirming the recently observed hyperhalogen behavior of superhalogen building blocks. ? 2011 American Chemical Society.EI03610237-1024311