Despite the large development of the field, the vast majority of systems exhibiting SCO behaviour contain an Fe II (d ) metal center, and there is an increasing interest on expanding the set of compounds with other metals and oxidation states exhibiting this behaviour. Similarly, while coordination chemistry has proven to be key in the design of ligands that generate the right splitting among the d-based molecular orbitals for the molecule to exhibit SCO, organometallic molecules usually have a larger ligand-field splitting that leads to low-spin states, and very few examples have been reported. Among the few organometallic SCO systems reported, the manganocene family ([Mn(Cp R ) 2 ]) has provided several examples of functionalized molecules exhibiting such behaviour. More relevant is the fact that the transition temperature (T 1/2 ), defined as the temperature with equal populations of both spin-states and a key physical property in SCO systems, can be modulated in such families via the R group.