was the most aromatic pentalenide species within this series. In each case, the NICS scan along the Z axis starting from the centre of one five-membered ring perpendicular to the plane of the pentalenide core is indicative of an aromatic ring current. The isotropic shift was negative throughout the scan, and the shape of the curve was mainly governed by the out-of-plane contributions to the isotropic shift with a clear minimum. For 1, the calculated NICS at that minimum (Z = 1.0 Å) was -28.6 ppm, which is in the same range as that of benzene (-29.1 ppm at 1.0 Å) and slightly higher than that of Cp - (-33.8 ppm at 0.9 Å). For 2 and 3 the minima were significantly higher than in 1, with -12.9 ppm for 2 and -12.5 ppm for 3 at 1.4 Å each (see also Figure ).