Symmetry breakings in a metal organic framework with a confined guest

The MOF [Fe(tvp)(2)(NCS)(2)]center dot 2BzCHO is demonstrated to undergo a complex sequence of phase transitions and spin-crossover behavior of its constitutive FeII ions upon adsorption of benzaldehyde guest molecules. Our study, combining Raman and synchrotron x-ray diffraction measurements on a 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 symmetries involve spinstate ordering, ligand ordering, and guest ordering, interpreted by combining magnetic susceptibility, Raman measurements, density functional theory, and force field molecular dynamics calculations.