Reversible Breaking and Forming of Metal–Ligand Coordination Bonds: Temperature‐Triggered Single‐Crystal to Single‐Crystal Transformation in a Metal–Organic Framework

The novel Yb succinate metal–organic framework exhibits a reversible single‐crystal to single‐crystal polymorphic transformation (see figure) when it is heated above 130 °C, returning to its initial form when back at room temperature. This transformation produces a change in the coordination sphere of the Yb atoms, which influences the catalytic activity of the material. magnified image [Yb(C 4 H 4 O 4 ) 1.5 ] undergoes a temperature‐triggered single‐crystal to single‐crystal transformation. Thermal X‐ray single‐crystal studies showed a reversibly orchestrated rearrangement of the atoms generated by the breaking/formation of coordination bonds, in which the stoichiometry of the compound remains unchanged. The transformation occurs on heating the crystal at ≈130 °C. This uncommon behavior was also studied by thermal methods, FTIR spectroscopy, and thermodiffractometry. Both polymorphs, α (room‐temperature form) and β (high‐temperature form), are proven to be active heterogeneous catalysts; the higher catalytic activity of β is owed to a decrease in the Yb coordination number. A mechanism based on spectroscopic evidence and involving formation of the active species YbOOH is proposed for the sulfide oxidation.