title: Al5O4: A Superatom with Potential for New Materials Design.
abstract: The Al5O4(-) cluster displays a highly symmetric (D4h) planar ring structure and magic cluster stability. The enhanced stability of this nonstoichiometric cluster is the result of an unconventional electronic distribution within the cluster, which is different from that found in stoichiometric Al2O3. The corresponding neutral Al5O4 cluster exhibits a strong electron affinity (3.5 eV) that is very close to that of a chlorine atom (3.6 eV). When interacting with the electropositive metals (M = Li, Na, K, etc.), the neutral cluster captures one electron and forms a "binary salt" composed of Al5O4(-) anion and M(+) cation. Interestingly, the geometric and electronic structure of bare Al5O4(-) is completely retained in the salt structure. This suggests that Al5O4 behaves as a superatom and Al5O4M is reminiscent of a diatomic ionic molecule such as NaCl or KCl. We have also demonstrated that Al5O4M can be used as a building block to construct new solid state materials. A detailed structural analysis of the monomer, dimer, and trimer of Al5O4M reveals that while M tends to coordinate with the cluster oxygen in monomeric Al5O4M, the binding preference is significantly changed in the presence of multiple metal and cluster ions. In this case, M favors coordinating to the terminal Al atoms in the cluster where the four highest occupied molecular orbitals are distributed. Based on these observations, we have designed new 1-D, 2-D, and 3-D extended networks using Al5O4M as the building block. The 3-D periodic lattice displays a structure similar to that in zeolites and, therefore, may exhibit behavior useful for applications as molecular sieves.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana 47405.
authors.forename: Ujjal
authors.initials: U
authors.lastname: Das
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, Indiana 47405.
authors.forename: Krishnan
authors.initials: K
authors.lastname: Raghavachari