The general picture of ligand dynamics. We first apply 2 H NMR on deuterated ligands to assess the time scale and characteristics of ligand motion. In principle, the 2 H quadrupolar splitting of a 2 H nucleus on a static CD2 unit is about 120 kHz displaying as a double-horn Pake pattern . When the motional rate of a CD2 unit is close to or faster than the splitting (~ 100 kHz), the 2 H pattern will be modified (i.e., motional averaged) according to the dynamic mode of the motion. For fast isotropic tumbling of molecules as seen in most liquids, the 2 H pattern will be averaged to a narrow line. For restricted segments, the motion is unusually not isotropic but has certain preferred symmetry, which will lead to characteristic 2 H patterns.