Symmetry breakings in a metal organic framework with a confined guest

Abstract

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.

Landau theory for non-symmetry-breaking electronic instability coupled to symmetry-breaking order parameter applied to Prussian blue analog

“…For example, it can describe the phase transition reported in few spin-crossover materials, for which the non-symmetry-breaking change of spin state (q) couples to a ferroelastic distortions () and result in a broad thermal hysteresis. 21,[63][64][65] The model also account for totally symmetric changes of electronic state in one-dimensional organic conductors coupled to ferroelastic distortion. 66 The phase diagram in Fig.…”

Halobenzene Clathrates of the Porous Metal–Organic Spin-Crossover Framework [Fe(tvp)2(NCS)2]n. Stabilization of a Four-Step Transition

“…In particular, up to three structural phases have been identified for 1@2PhCHO in a recent detailed study, mentioned above, that combines variable-temperature synchrotron X-ray diffraction measurements (to determine the long-range order and symmetry lowering) and molecular dynamics simulations (to explore the structure of the guest confined in the channels). 42 …”

Spin-crossover materials: Getting the most from x-ray crystallography

“…The dynamics of the phase transition has been interpreted using a structural model built in a wide variety of long-range ordered patterns of HS and LS molecules. [75][76][77][78][79][80]70 Up to now, spin state transitions with up to eight more or less clearly identified steps have been reported. In most of the cases, the crystal structure has been solved for all the steps, allowing a clear description of the HS/LS supramolecular ordering.…”

“…The spin state ordering component is described by the spatial probability for a site at position to be in the HS state, which in the harmonic approximation writes 70,79 :…”