The role of molecular vibrations in the spin crossover phenomenon

The prominent role of intra- and inter-molecular vibrations in the spin crossover phenomenon is outlined, based on the results obtained by the spin crossover community. The experimental results gained from various techniques (IR, Raman, X-ray diffraction, heat capacity, Mossbauer spectroscopy, synchrotron radiation techniques, etc.) and their interpretation are described. The contribution of theoretical models (thermodynamic and Ising-like electro-vibrational,models) to the understanding of the relationship between the relative energies of the high-spin and low-spin states and molecular vibrations, especially when the high-spin and low-spin energy levels are close to each other, is stressed.