Temperature-, Pressure- and Light-Induced Electronic Spin Conversions in Transition Metal Complexes

High spin ↔ low spin electronic spin crossovers may be observed in a number of transition metal complexes when the ligand-field and electron-pairing energies happen to be comparable in magnitude. They are obtained under the effect of an external perturbation such as a variation of temperature, a variation of pressure or an irradiation with light. These three ways of inducing spin conversions are presented.