Vibrational Spectroscopy of Mono- and Polynuclear Spin-Crossover Systems

Vibrational spectroscopy can be used to follow spin transition processes, induced by a change of temperature, pressure, or irradiation with light of suitable wavelength, in spin-crossover (SCO) molecules. In this contribution, recent applications of infrared and Raman spectroscopy, as well as nuclear inelastic scattering (NIS), are reviewed. In the past, vibrational spectroscopic methods have been used to identify spin marker bands that reflect the different spin states in a sample. This application is certainly still one of the major ones and is used especially in connection with mode assignments by modern density functional calculations. However, during the last years also major progress has been achieved (1) in studying nano- and microstructures of SCO complexes, (2) in the search for spin domains, and (3) also in the investigation of the spin switch process itself, which is nowadays studied not only by ultrafast time-dependent UV/Vis spectroscopy, but also by femtosecond IR and Raman spectroscopy.