Molecular dynamics in paramagnetic materials as studied by magic-angle spinning 2H NMR spectra

A magic-angle spinning (MAS) H-2 NMR experiment was applied to study the molecular motion in paramagnetic compounds. The temperature dependences of H-2 MAS NMR spectra were measured for paramagnetic [M(H2O)(6)]-[SiF6] (M = Ni2+, Mn2+, CO2+) and diamagnetic [Zn(H2O)(6)][SiF6]. The paramagnetic compounds exhibited an asymmetric line shape in 2 H MAS NMR spectra because of the electron-nuclear dipolar coupling. The drastic changes in the shape of spinning sideband patterns and in the line width of spinning sidebands due to the 180 degrees flip of water molecules and the reorientation of [M(H2O)6](2+) about its C-3 axis were observed. In the paramagnetic compounds, paramagnetic spin-spin relaxation and anisotropic g-factor result in additional linebroadening of each of the spinning sidebands. The spectral simulation of MAS H-2 NMR, including the effects of paramagnetic shift and anisotropic spin-spin relaxation due to electron-nuclear dipolar coupling and anisotropic g-factor, was performed for several molecular motions. Information about molecular motions in the dynamic range of 102 S-1 <= k <= 10(8) S-1 can be obtained for the paramagnetic compounds from the analysis of H-2 MAS NMR spectra when these paramagnetic effects are taken into account.