ChemInform Abstract: Gold Behaves as Hydrogen in the Intermolecular Self-Interaction of Metal Aurides MAu4 (M: Ti, Zr, and Hf)

We performed density functional calculations to examine the intermolecular self-interaction of metal tetraauride MAu(4) (M = Ti, Zr, and Hf) clusters. We found that the metal auride clusters have strong dimeric interactions (2.8-3.1 eV) and are similar to the metal hydride analogues with respect to structure and bonding nature. Similarly to (MH(4))(2), the (μ-Au)(3) C(s) structures with three three-center two-electron (3c-2e) bonds were found to be the most stable. Natural orbital analysis showed that greater than 96 % of the Au 6s orbital contributes to the 3c-2e bonds, and this predominant s orbital is responsible for the similarity between metal aurides and metal hydrides (>99 % H 1s). The favorable orbital interaction between occupied Au 6s and unoccupied metal d orbitals leads to a stronger dimeric interaction for MAu(4)-MAu(4) than the interaction for MH(4)-MH(4). There is a strong relationship between the dimeric interaction energy and the chemical hardness of its monomer for (MAu(4))(2) and (MH(4))(2).