Reorientational motion of cobaltocene intercalated into titanium diselenide: NMR study

To study the dynamics of cobaltocene molecules Co($\pi$–C$_5$H$_5$)$_2$ intercalated into quasi-two-dimensional titanium diselenide TiSe$_2$, we have measured the proton spin-lattice relaxation times and $^1$H nuclear magnetic resonance (NMR) spectra in TiSe$_2$(Co($\pi$–C$_5$H$_5$)$_2$)$_{1/4}$ compound over the temperature range of 5 – 360 K. The existence of two types of reorientational motion of Co($\pi$–(C$_5$H$_5$)$_2$) molecules has been found. The faster reorientational process related to rotations of C$_5$H$_5$ rings around the 5-fold symmetry axis is characterized by the activation energy of 60 meV, and the slower process determined by reorientations of cobaltocene molecules around the 2-fold symmetry axis is characterized by the activation energy of 155 meV. Measurements of $^1$H NMR parameters in molecular cobaltocene have shown that for this compound the dominant mechanism of the proton spin-lattice relaxation is determined not by motion of Co($\pi$–(C$_5$H$_5$)$_2$) molecules, but by fluctuations of the localized electronic magnetic moment on cobalt.