Variable temperature C-13-{H-1} CP/MAS, H-1 MAS and H-1 wide-line NMR
spectra of H4Ru4-(CO)12 are interpreted in terms of a dynamic process
involving either the H4RU4 moiety as a whole or the motion of the hydr
ides over the surface of the metallic core. The temperature dependence
of the H-1 spin-lattice relaxation time (T1) values over the range 29
8-360 K and the temperature dependence of the line width of the static
H-1 spectrum over the range 153-380 K together give an activation ene
rgy for this motional process of 67.2 +/- 8.0 kJ mol-1. The rigidity o
f the carbonyl polyhedron is demonstrated by the fact that the C-13 ch
emical shift tensor components are typical for those in a nonfluxional
molecule and are invariant between 200 and 360 K.