Aromaticity of [M₃(µ-X)₃X₆]^0/2– (M = Re and Tc, X = Cl, Br, I) Clusters Confirmed by Ring Current Analysis and Induced Magnetic Field

We present new evidence that supports the aromatic character of the clusters of formula: [M₃(µ-X)₃X₆]^0/2– (M = Re and Tc, X = Cl, Br, I). Our computations clearly show that these clusters present a special response to an applied external magnetic field, which is characteristic of aromatic systems. Both analyzed response properties, the magnetically induced current density and the induced magnetic field, agree that the magnetic perturbation induces two concentric diatropic ring currents: the inner one inside the M₃ core and the outer one around the M₃(µ-X)₃ triangle. The flow strength of these two ring currents is significant, confirming the high diatropicity of these clusters. In the dianionic species, aromaticity is increased, mainly by an increment of the diatropicity of the inner ring current. These findings support a chemical bonding pattern with delocalized M–M bonds in these species.