Theoretical study on the assembly and stabilization of a magic cluster Al4N-

We report the first attempt to assemble the magic cluster Al4N- on the basis of the density functional theory calculations on a series of pi-stacked dimers (Al4N-)2, sandwich-like compounds D(Al4N)M]q- (where D = Al4N-, Cp-(C5H5-); M = Li, Na, K, Be, Mg, Ca) and extended compounds (Cp-)m(Li+)n(Al4N-)o (where m, n, and o are integers). For the six metals, the magic Al4N- can only be assembled and grow up in our newly proposed "hetero-decked sandwich" scheme (e.g., CpM(Al4N)]q-) so as to avoid cluster fusion. The ground-state hetero-decked sandwich species (Cp-)(M)q+(Al4N)- (M = Li, Na, K, q = 1; M = Be, Mg, Ca, q = 2) and the extended sandwich species (Cp-)m(Li+)n(Al4N-)o are mainly ionically bonded, cluster-assembled "polyatomic molecules", grown from the combination of Cp-, M-atoms, and Al4N-. As a prototype for ionic bonding involving intact Al4N- subunits, CpM(Al4N)]q- may be a stepping stone toward forming ionic, cluster-assembled AlN compounds.