Symmetry breakings in a metal organic framework with a confined guest

The MOF [F e(tvp) 2 (N CS) 2 ] · 2BzCHO is demonstrated to undergo a complex sequence of phase transitions and spin crossover behavior of its constitutive F e II ions upon adsorption of benzaldehyde guest molecules. Our study, combining Raman and synchrotron X-ray diffraction measurements on single crystal reveals that the conversion from the pure high spin to the pure low spin phases implies a rich sequence of intermediate phases, with symmetry breaking forming at least three different space groups. These different symmetry involve spin-state ordering, ligand ordering and guest ordering, interpreted by combining magnetic susceptibility, Raman measurements, Density Functional Theory and force field Molecular Dynamics calculations.