Al5O4: A Superatom with Potential for New Materials Design

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• 作者：Ujjal Das ; Krishnan Raghavachari
• 刊名：Journal of Chemical Theory and Computation
• 出版年：2008
• 出版时间：December 9, 2008
• 年：2008
• 卷：4
• 期：12
• 页码：2011-2019
• 全文大小：368K
• 年卷期：v.4,no.12(December 9, 2008)
• ISSN：1549-9626

文摘

The Al₅O₄⁻ cluster displays a highly symmetric (D_4h) 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.