Wavelength selective light-induced magnetic effects in the binuclear spin crossover compound {[Fe(bt)(NCS)2]2(bpym)}

Nawell Ould-Moussa (1) , Elzbieta Trzop (2) , S. Mouri (3) , Samir Zein (4, 5) , Gábor Molnár (1) , Ana B. Gaspar (6) , Eric Collet (2) , Marylise Buron-Le Cointe (2) , José Antonio Real (6) , Sergei Borshch (5) , Katsumi Tanaka (3) , Hervé Cailleau (2) , Azzedine Bousseksou (1)

1 LCC - Laboratoire de chimie de coordination
2 GMCM - Groupe matière condensée et matériaux
3 Department of Physics
4 ENS de Lyon - École normale supérieure de Lyon
5 LC - Laboratoire de Chimie - UMR5182
6 ICMol - Instituto de Ciencia Molecular

Using Fourier transform infrared spectroscopy, x-ray diffraction, and magnetic susceptibility measurements under light irradiation, the selective light-induced excited spin state trapping (LIESST) and the reversible-LIESST effect have been evidenced and studied in depth in the binuclear spin crossover compound {[Fe(bt)(NCS)2]2bpym}. In this system, each magnetic site can switch from low spin (LS) to high spin (HS), so that three states exist, namely, the LS-LS, HS-LS, and HS-HS. All these techniques shine a new light on the high phototunability of this system. In addition to the direct photoswitching from the LS-LS to the HS-LS or to the HS-HS state, here we show that photoinduced switching between the excited photoinduced states can be triggered in a reversible way: from HS-LS to HS-HS (irradiation around 800 nm), or reverse from HS-HS to HS-LS (irradiation around 1300 nm). The nature of the intermediate HS-LS state during the thermal and light-induced spin state changes is also discussed by comparing the spectroscopic measurements and the structural analysis. The loss of inversion symmetry in the HS-LS molecular state, where the two magnetic Fe sites are no more equivalent, is not accompanied by any long-range ordering of the noncentrosymmetric molecules in the crystal. Therefore the continuous double-step spin conversion corresponds to a double crossover.

Domaines: Physique Atomique [physics.atom-ph]

Nawell Ould-Moussa, Elzbieta Trzop, S. Mouri, Samir Zein, Gábor Molnár, et al.. Wavelength selective light-induced magnetic effects in the binuclear spin crossover compound {[Fe(bt)(NCS)2]2(bpym)}. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2007, 75 (5), pp.054101. ⟨10.1103/PhysRevB.75.054101⟩. ⟨hal-00906085⟩