In general, a decrease in the T 1/2 is observed with increasingly withdrawing character of the R group. Although this trend in the computed T 1/2 spans on a 500 K range, the geometries of the computed systems remains almost identical, as can be observed using the average Mn-Cp centroid-distance. For all systems in Table , this parameter has average values of 1.734 Å and 2.092 Å for the low-and high-spin states, respectively (standard deviations of 0.0047 and 0.0082, see Supporting Information). This clearly shows the electronic nature of the tuning effect that the R group has on the SCO properties of the [Mn(Cp R ) 2 ] family. family (M = Cr II , Mn II , Fe II and Co II ). The computed energy gaps are in all cases larger than for the [Mn(Cp 1-Me ) 2 ] case (see Supporting Information), but the [Cr(Cp 1-Me ) 2 ] is close enough so one can envision a tuning of the ligand field to achieve SCO. Therefore, we replaced the methyl group by electron withdrawing groups (R=NO 2 and CN)