The LIESST state of [Fe(pic)3]Cl2.EtOH – the superstructure under continuous irradiation

The superstructure recently discovered in [Fe(pic)(3)] Cl(2)center dot EtOH at temperatures inside the step region of the high-spin-low-spin transition curve sheds new light on the anomalous transition behaviour in spin crossover compounds. The structure of the metastable LIESST state of [Fe(pic)(3)] Cl(2)center dot EtOH at 10 K has been measured. The decay has been followed by X-ray diffraction using a CCD camera in order to detect reflections of the superstructure building up during the decay. No signal above the noise of the CCD camera was observed, so that even diffuse scattering could not be detected. This finding is in agreement with correlation lengths of pair correlations of molecules in the HS and LS states being very short, as was concluded earlier from the shape of the decay curves of the HS fraction by theoretical considerations [Romstedt et al. ( 1998). J. Phys. Chem. Solids, 59, 265 - 275]. The crystal structure inside the step at 118 K has also been studied under continuous irradiation. The temperature range of the superstructure and the degree of order could be changed by continuous irradiation with green laser light, indicating an increase of the lifetime of the HS excited state by several orders of magnitude compared with the temperature regions outside.