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Rotational Ligand Dynamics in Mn[N(CN)2]2.pyrazine Group

This material consists of transition metal ions linked by polydentate organic ligands, forming different structures at low and high temperatures. At 1.3K, it exhibits 3D antiferromagnetic order in a monoclinic lattice; around 200K, it transforms into an orthorhombic structure. Analysis at ~408K shows an additional phase transition. Neutron scattering is used due to wavelength and energy compatibility with interatomic distances and motion dynamics for simultaneous geometric and time-scale insight. It differentially interacts with hydrogen and deuterium, has a magnetic moment, and directly interacts with nuclei. Experimental runs on protonated and deuterated samples with the Disc-Chopper Spectrometer provide crucial scattering data. Coherent and incoherent scattering reveal diffusional motion of protons, with results indicating a thermally activated jump motion starting at 200K, evolving the framework structure.

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Rotational Ligand Dynamics in Mn[N(CN)2]2.pyrazine Group

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  1. Rotational Ligand Dynamics in Mn[N(CN)2]2.pyrazine Group C Jun Tian, Wei Zhou, Greg Hura, Vicky Garcia Sakai, Chris Kitchens, Joon Ho Roh, Amit Kumar, Yifu Ding

  2. Mn[N(CN)2]2.pyrazine • material consisting of transition metal ions linked by polydentate organic ligands • forms different structures at low and high temperatures • at 1.3K 3D antiferromagnetic order, monoclinic lattice • ~ 200K orthorhombic structure • ~ 408K DSC shows additional phase transition ?

  3. Why use neutron scattering? • Have wavelengths comparable to interatomic distances and energies comparable to phonon and intermolecular interaction energies  obtain information on geometry and time-scale of motions simultaneously • Interact differently with H and D • Have a magnetic moment • Interact directly with the nucleus

  4. Disc-Chopper Spectrometer • Experimental runs • protonated (T=395, 405, 415, 425K) • deuterated (T=300, 390, 400K) • vanadium • background

  5. Measured Scattering • Incoherent scattering dominated by protons • Sinc(Q,w) is the space and time FT of the self-correlation function..probability of finding a particle at time t in position r given that it was at the origin at time t=0 • Fit using model such as diffusional motion of protons among equivalent sites Elasticcontribution Inelasticcontribution

  6. Results 395K 425K

  7. Results T=425K

  8. Conclusion A thermally activated 2-fold jump motion about the coordinating nitrogen axis takes place which actually starts at 200K. At 408K more pyrazine rings perform this motion and a more open framework structure forms. Thanks to the organizers!

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