These results suggest that tetrahedral arrangements favour dative covalent interactions. In fact, when we calculate the total delocalization indexes by summing all δ X-Zn (Figure ), tetrahedral clusters show in all cases a higher value than octahedral ones, indicating a higher covalent nature of the interaction in tetrahedral arrangements than in octahedral ones. We also observe that as the number of imidazoles increases, the total delocalization of each cluster also increases. Nevertheless, a slight decrease of the total delocalization is observed in the case of the octahedral [Zn(Im) 4 ] 2+ cluster with respect to [Zn(Im) 3 (Ac) 1 ] + .