H-2 NMR study of molecular and electron spin dynamics in paramagnetic [Co(H2O)(6)][SiF6]

The temperature dependences of H-2 NMR spectra and the spin-lattice relaxat ion time T-1 were measured for [Co(H2O)(6)][SiF6]. The variation of the spe ctrum above room temperature can be explained by the reorientation of [Co(H 2O)(6)](2+) about the C-3 axis. The activation energy E-a, and the jumping rate at infinite temperature k(0) for the three site jump of [Co(H2O)(6)](2 +) were obtained as 82 kJmol(-1) and 2x10(17)s(-1) from the spectral simula tion. Below room temperature, the spectral line shape was; dominated by the 180 degrees flip of the water molecule. The minimum of T-1 caused by the 1 80 degrees flip of the water molecule was observed at ca. 260 K. The jumpin g rate of the 180 degrees flip of the water molecule was estimated from the H-2 NMR T-1 and the spectral simulation. E-a = 38 kJmol(-1) and k(0) = 6 x 10(15)s(-1) for the 180 degrees flip of the water molecule were obtained f rom T-1.