Molecular dynamics and phase transitions in paramagnetic [Mn(H2O)6][SiF6] investigated by 2H NMR

• Published in: The Journal of physics and chemistry of solids 2005-06, Vol.66 (6), p.1101-1106
• Main Authors: Iijima, Takahiro, Hamada, Keigo, Mizuno, Motohiro, Endo, Kazunaka, Suhara, Masahiko
• Format: Article
• Language: English
• Subjects: A. Inorganic compounds; Condensed matter: electronic structure, electrical, magnetic, and optical properties; D. Nuclear magnetic resonance; D. Phase transitions; Exact sciences and technology; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Nuclear magnetic resonance and relaxation; Physics
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2005.02.007

The temperature dependences of 2H NMR spectra and spin-lattice relaxation time T1 have been measured for paramagnetic [Mn(H2O)6][SiF6]. The obtained 2H NMR spectra were simulated by considering the quadrupole interaction and paramagnetic shift. The variation of the spectra measured in phase III was explained by the 180° flip of water molecules. The activation energy Ea and the jumping rate at infinite temperature k0 for the 180° flip of H2O were obtained as 35kJmol−1 and 4×1014s−1, respectively. The spectral change in phases I and II was ascribed to the reorientation of [Mn(H2O)6]2+ around the C3 axis where the Ea and k0 values were estimated as 45kJmol−1 and 1×1013s−1, respectively. From the almost temperature independent and short T1 value, the correlation time for electron-spin flip-flops, τe, and the exchange coupling constant J were obtained as 3.0×10−10s and 2.9×10−3cm−1, respectively. The II–III phase transition can be caused by the onset of the jumping motion of [Mn(H2O)6]2+ around the C3 axis.