In this work, we presented a robust computational methodology to study the spincrossover behaviour of manganocenes of general formula [Mn(Cp 1-R ) 2 ]. The combination of the OLYP exchange correlation functional with a triple- basis set with polarization functions on all atoms provides a computed T 1/2 in excellent agreement with the available experimental data for the [Mn(Cp 1-Me ) 2 ] system. Also, geometrical parameters are properly reproduced. Single functionalization of the cyclopentadienyl ring allows for a fine-tuning of the SCO properties in this family. A general trend is observed with the electron-donating character of the R group. In general, the more electron-donating the R group is, the higher the T 1/2 . The electronic modulating effect of the R group is validated by the almost non-existing changes in the geometries of the studied systems, all of them having a very similar Mn-Cp distance in both spinstates. The use of R groups to increase or decrease the transition temperature opens the door for the use of other metals aside from manganese, which so far is the only one able to exhibit SCO in metallocenes. In particular, we showed that chromocene has a spin-state energy gap that can, in principle, be tuned using electron-withdrawing R groups such as CN or NO 2 . Although single functionalization of the Cp ring with such substituents does indeed reduce the spin-state energy gap, it is not enough to achieve a reasonable T 1/2 due to the much lower electronic entropic contribution from Cr II compared to the one provided by Mn II . However, this can be bypassed by introducing a second NO 2 group to the ring. Thus, our calculations not only allow for a rational understanding on how to tune the SCO properties of the [Mn(Cp 1-R ) 2 ] family, but also open the door for the computational design of new metallocenes with tailored spin-crossover properties that expand the current library of such compounds.