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Solid-state ligand dynamics in interpenetrating Mn[N(CN)(2)](2)(pyrazine): a neutron spectroscopy study
Craig M Brown1, Jamie L Manson
1Department of Materials and Nuclear Engineering, University of Maryland, College Park, Maryland 20742, USA.
Journal of the American Chemical Society
|October 17, 2002
Summary
Solid-state ligand dynamics in interpenetrating coordination polymers were studied. Rotational dynamics of pyrazine ligands drive a reversible phase transition at 410 K.
Area of Science:
- Solid-state chemistry
- Materials science
- Neutron scattering
Background:
- Coordination polymers with interpenetrating lattices exhibit unique properties.
- Understanding ligand dynamics is crucial for material functionality.
- Solid-state rotational dynamics in such complex structures remain largely unexplored.
Purpose of the Study:
- To investigate the solid-state ligand dynamics in the double-interpenetrating 3D coordination polymer Mn[N(CN)2]2(pyz).
- To elucidate the origin of the reversible structural phase transition observed at 410 K.
- To characterize the rotational motion of pyrazine ligands and its temperature dependence.
Main Methods:
- Quasielastic neutron scattering (QENS) was employed to probe ligand dynamics.
- Differential scanning calorimetry (DSC) was used to identify the phase transition.
- High-resolution backscattering spectroscopy provided detailed motional analysis.
Main Results:
- A reversible structural phase transition was confirmed at 410 K.
- The transition is driven by the rotational dynamics of bridging pyrazine (pyz) ligands.
- At 425 K, pyrazine rings exhibit 180-degree reorientational jumps (τ ≈ 70 ps).
- Similar motion on the nanosecond timescale with an activation energy of 24 ± 2 kJ mol⁻¹ was observed between 200-410 K.
- No quasielastic scattering was detected in a 2D layered variant (β-Cu[N(CN)2]2(pyz)).
Conclusions:
- This study provides the first investigation of solid-state rotational dynamics in an interpenetrating lattice structure.
- The rotational dynamics of pyrazine ligands are directly linked to the observed phase transition.
- The findings highlight the importance of lattice architecture in dictating molecular motion and phase behavior.
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