Freezing of molecular rotation in a paramagnetic crystal studied by P-31 NMR

Article

关键词: COUPLING-CONSTANTS;    PHASE-TRANSITION;    SPIN DYNAMICS;    RELAXATION;    MOTION;    REORIENTATION;    K3C60;   

DOI  :  10.1103/PhysRevB.103.014428

来源: SCIE

【 摘 要 】

We present a detailed (31)p nuclear magnetic resonance (NMR) study of the molecular rotation in the compound [Cu(pz)(2)(2-HOpy)(2)](PF6)(2), where pz = C4H4N2 and 2-HOpy = C5H4NHO. Here, a freezing of the PF 6 rotation modes is revealed by several steplike increases of the temperature-dependent second spectral moment, with accompanying broad peaks of the longitudinal and transverse nuclear spin-relaxation rates. An analysis based on the Bloembergen-Purcell-Pound (BPP) theory quantifies the related activation energies as E-a/k(B) = 250 and 1400 K. Further, the anisotropy of the second spectral moment of the P-31 absorption line was calculated for the rigid lattice, as well as in the presence of several sets of PF6 reorientation modes, and is in excellent agreement with the experimental data. Whereas the anisotropy of the frequency shift and enhancement of nuclear spinrelaxation rates is driven by the molecular rotation with respect to the dipole fields stemming from the Cu ions, the second spectral moment is determined by the intramolecular interaction of nuclear F-19 and P-31 moments in the presence of the distinct rotation modes.

【 授权许可】

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