Extraordinary superatom containing double shell nucleus: Li(HF)(3)Li connected mainly by intermolecular interactions

摘要

The structure and properties of the Li(HF)3Li cluster with C-3h symmetry are investigated using ab initio calculations. This Li(HF),Li is a metal-nonmetal-metal sandwich-like cluster connected mainly by the intermolecular interactions. In the special cluster, the (HF), containing the triangular F ring with the, negative charges is sandwiched between two Li atom. It is interesting that under the action of the triangular F ring with the negative charges, the valence electrons of two Li atoms are pushed out to form the distended excess electron cloud that surrounds the Li(HF)(3)Li as a core. So the Li(HF)(3)Li cluster shows not only the electride characteristic, but new superatom characteristics as well. Several characteristics of the special superatom are found. First, the superatom contains the double shell nucleus. The internal nucleus is the regular triangular ring made of three F atoms with the negative charge and the outer-shell nucleus is made up of three H and two Li atoms with the positive charge. Second, the bonding force of this superatom framework is mainly the intermolecular interaction force, the lithium bond, which is different from that (covalent bond or ionic bond) of the general superatom. Third, the interaction between the outer-shell nucleus and the excess electron cloud is mainly the anti-excess-electron hydrogen bond. Fourth, the special superatom exhibits the new aromaticity (NICS = -8.37 ppm at the center of the regular triangular F ring), which is the aromaticity found in the cluster of the intermolecular interaction. This is the new knowledge of the aromaticity. Fifth, the large polarizability of the superatom is revealed. Further, the vertical ionization energy (VIE) of the superatom is low, 4.51 eV (< 5.210 eV of the alkaline-earth metal Ba) so that it may be viewed as a superalkaline-earth metal atom. (c) 2006 Wiley Periodicals, Inc.