Five atoms of gold

2- and 3-coordinated atoms. The smallest separations, 2.68-2.70 A, are found between 2- and 4-coordinated atoms. The spin-up and spin-down gaps, Ehlt EhU) equal to about 2.5 and 2.2 eV, respectively, at the B3LYP computational levels and 1.6 and 1.0 eV at BP86/A and PW91/A (see Fig. 1). 

Two higher in energy clusters, AuP and Aus, are reported in the present work for the first time. They fill the energy gap between the 2D clusters AU5 and Auf and the 3D pyramid which is about 21.4 kcal/mol above AU5 [44]. Both these two novel structures are less compact, less coordinated, polar (1.2 D and —4.2 D, respectively) and characterized by rather large polarizabilities 

Aus and Au are also rather different in the MO patterns that determine their catalytic reactivity. The Aus HOMO-1-HOMO and HOMO-LUMO gaps are equal to 0.94 [1.01 1.00] eV (see Ref. [67]) and 1.21 [0.93 1.09] eV, respectively. In Au the HOMO-1-HOMO gap is substantially narrower, viz., 0.27 [0.23 0.30] eV while the HOMO-LUMO one is wider and equal to 2.88 [2.39 2.41] eV. The EAgS and VDEs of these anionic clusters are indicated in Fig. 2. The EAg and VDE of Aus are comparable with the experimental data and, as shown in Fig. 1, such comparison is fairly satisfactory. The neutral parent of Aus is the ground-state cluster Aus whereas the neutral parent of AuP is the higher energy isomer Aus discussed above. On the neutral PES, the transition state between Aus 

All quantities are displayed in the following order (from top to bottom)  

It is worth mentioning that two electrons can be simultaneously attached to Au to form the dianion Au shown in Fig. 3. This dianion is stable relative to Au with a total energy difference of 65.6 kcal/mol (65.8 kcal/ mol after ZPVE) although it still remains unstable with respect to the corresponding anion Aus by 28.8 kcal/mol (28.6 kcal/mol after ZPVE). It is responsible for the second adiabatic electron affinity (see Ref. [68]). This first implies that such a dianion may exist in solvent or condensed phase (see Ref. [69] for current review) and second, that it does not exist in the gas phase and, therefore, there is no contradiction with the statement that the smallest stable dianion is Aui2 [70]. 

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