Spin-state ordering on one sub-lattice of a mononuclear iron(III) spin crossover complex exhibiting LIESST and TIESST

The two-step spin crossover in mononuclear iron(III) complex [Fe(salpm)2]ClO4{dot operator}0.5EtOH (1) is shown to be accompanied by a structural phase transition as concluded from 57Fe Mössbauer spectroscopy and single crystal X-ray diffraction, with spin-state ordering on just one of two sub-lattices in the intermediate magnetic and structural phase. The complex also exhibits thermal- and light-induced spin-state trapping (TIESST and LIESST), and relaxation from the LIESST and TIESST excited states occurs via the broken symmetry intermediate phase. Two relaxation events are evident in both experiments, that is, two T(LIESST) and two T(TIESST) values are recorded. The change in symmetry which accompanies the TIESST effect was followed in real time using single crystal diffraction. After flash freezing at 15K the crystal was warmed to 40K at which temperature superstructure reflections were observed to appear and disappear within a 10000s time range. In the frame of the international year of crystallography, these results illustrate how X-ray diffraction makes it possible to understand complex ordering phenomena. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim