Spin-State Ordering on One Sub-lattice of a Mononuclear Iron(III) Spin Crossover Complex Exhibiting LIESST and TIESST

• Published in: Chemistry : a European journal 2014-05, Vol.20 (19), p.5613-5618
• Main Authors: Murnaghan, Kevin D., Carbonera, Chiara, Toupet, Loic, Griffin, Michael, Dîrtu, Marinela M., Desplanches, Cédric, Garcia, Yann, Collet, Eric, Létard, Jean-François, Morgan, Grace G.
• Format: Article
• Language: English
• Subjects: Broken symmetry; Chemical Sciences; Chemistry; Crossovers; Diffraction; Excitation; iron; LIESST; magnetic properties; Material chemistry; Order disorder; Phase transformations; Single crystals; TIESST; Trapping
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201400286

The two‐step spin crossover in mononuclear iron(III) complex [Fe(salpm)2]ClO4⋅0.5 EtOH (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 15 K the crystal was warmed to 40 K at which temperature superstructure reflections were observed to appear and disappear within a 10 000 s 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. Called to order: Real‐time single‐crystal diffraction is used to follow the dynamics of a symmetry‐breaking magnetic and structural phase transition in a mononuclear iron(III) spin crossover complex, which also exhibits a rare LIESST excitation. The thermal symmetry breaking results in spin‐state ordering involving just one of the two sub‐lattices in the intermediate (INT, see figure) structural phase which is also accessible by LIESST and TIESST (LIESST=Light‐induced excited spin‐state trapping, TIESST=thermal‐induced excited spin‐state trapping).