Precessional Motion in Crystalline Solid Solutions of Ionic Rotors.

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Investigating order-disorder phase transitions in supramolecular salts of the formula [1·(DABCOH2)]X2.
• Understanding the reorientational motion of (DABCOH2)2+ dications.

Purpose of the Study:

• To investigate the order-disorder phase transition in [1·(DABCOH2)]X2 supramolecular salts.
• To characterize the dynamic processes and structural changes associated with the transition.
• To identify novel dynamic phenomena in the (DABCOH2)2+ dications.

Main Methods:

• Variable temperature X-ray diffraction (single crystal and powder).
• Differential Scanning Calorimetry (DSC).
• Solid-state Nuclear Magnetic Resonance (SSNMR) spectroscopy, including 13C MAS NMR.
• Line-shape analysis.

Main Results:

• Two compounds, [1·(DABCOH2)]Cl2 and [1·(DABCOH2)]Br2, exhibit reversible phase transitions at 292 K and 290 K, respectively.
• Solid solutions [1·(DABCOH2)]Cl2xBr2(1-x) form across the entire composition range, with transition temperatures decreasing to a minimum of ~280 K at x=0.5.
• A novel room-temperature precessional motion of (DABCOH2)2+ dications was detected, which freezes out below the order-disorder transition.

Conclusions:

• The study elucidates the order-disorder phase transition mechanism in these supramolecular salts.
• A new type of dynamic behavior, precessional motion, has been identified in (DABCOH2)2+ dications.
• The findings contribute to the understanding of molecular dynamics in crystalline materials.