REORIENTATIONAL MOTIONS OF PERMETHYLATED CYCLOPENTADIENYL RINGS IN POLYCRYSTALLINE ORGANOMETALLIC COMPOUNDS

The dynamic behavior in the solid state of (C 5 Me 5 ) 2 Fe (I), (C 5 Me 5 )Rh(CO) 2 (II), (C 5 Me 5 ) 2 Cr 2 (C 4 ) (III), (C 5 Me 5 )Fe 2 (μ 2 -CO) 2 (CO) 2 (IV), and (C 5 Me 5 ) 2 Rh 2 (μ 2 -Cl) 2 Cl 2 (V) has been investigated by variable-temperature 1 H spin-lattice relaxation time measurements and potential energy barrier calculations within the pairwise atom-atom approach. Two different processes have been detected corresponding to the rotation of the methyl group about its C 3 axis and to the reorientation of the cyclopentadienyl ligand about its C 5 axis, respectively