Structures and stability of B-doped Al anions: Al_nB^- and Al_nB₂^- (n = 1-7)

Various structural possibilities for Al_nB_m^- (m + n = 3-8, m = 1-2) anionic isomers were investigated using B3LYP/6-31+G(d) and CCSD(T)/6-31+G(d) methods. Our calculations predicted the existence of a number of previously unknown isomers. All structures of the Al_nB^- (n = 2-6) may be derived from a substitution of an Al atom by a B atom in the Al_n+1^- anions while the geometrical structure of Al₇B^- may be understood as putting centrally a B atom inside the Al₇^- cage-like structure. The strong B{single bond}B bond is dominant factor in building-up principle of mixed Al_nB₂^- (n = 1-6) anions. All Al_nB_m^- with odd n + m (2 < n + m < 9) are relatively more stable. Our present results satisfactorily explain the photoelectron spectroscopy and finally improve our understanding of these experimental observations.