Photoinduced spin crossover in a Fe-picolylamine complex:: A far-infrared study on single crystals -: art. no. 073108

Far-infrared spectroscopy has been performed on [Fe(2-picolylamine)(3)]Cl2EtOH (Fe-pic) single crystals to probe changes in the molecular vibrations upon the photoinduced and temperature-induced spin crossovers. Synchrotron radiation has been used as the far-infrared source to overcome the strong absorption and the small sizes of the samples. Absorption lines due to FeN6 cluster vibrations, observed below 400 cm(-1), show strong intensity variations upon the crossover due to the compression/expansion of FeN6 between high-spin and low-spin states. However, they remain almost unchanged between the photo- and temperature-induced high-spin states. This is in sharp contrast to the lines at 500-700 cm(-1) due to intramolecular vibrations of the picolylamine ligands, which show marked variations between the two high-spin states. It is concluded that the most important microscopic difference between the two high-spin states arises from the ligands, which are likely to reflect different states of intermolecular bonding.