In Figure , we show the relative energies between tetrahedral and octahedral clusters. ∆∆H T/O energies using both the FCS and FCS+2W approaches indicate that the tetrahedral geometry is favored in the solvent phase except for the [Zn(Im) 2 (Ac) 2 ] and [Zn(Im) 3 (Ac) 1 ] + clusters in the FCS approach. On the other hand, both ∆∆G T/O and ∆∆G T/O 1/2 energies clearly favour tetrahedral coordination for all clusters (see Table ). Therefore, from these calculations we conclude that the preferred Aβ-Zn(II) systems in the solvent phase are the tetrahedrally coordinated [Zn(Im) 2 (Ac) 2 ] and [Zn(Im) 3 (Ac) 1 ] + clusters. Interestingly these two clusters exhibit the lowest difference in energy between octahedral and tetrahedral coordination.