1H NMR Studieson the Molecular Dynamics of Acetylferrocene in Crystals

Abstract

Abstract The temperature dependence of 1H spin-lattice relaxation time was determined at 20 MHz for solid acetylferrocene [(C5H5) (C5H4COCH3)Fe] from ca. 80 K up to the m.p. (359 K). Rather large activation energies of 21 and 24 kJ mol-1 for the C5 reorientations of the two crystallographically nonequivalent non-substituted cyclopentadienyl rings were obtained, indicating that the crystal has a closely packed structure. The two kinds of CH3 groups attached to the substituted cyclopenta­dienyl rings were assumed to be approximately equivalent and gave a low activation energy of 4 kJ mol-1 for the C3 reorientation. No phase transition was observed in the relaxation times or in additional experiments of differential thermal analysis although the presence of two phase transi­tions has been reported previously at temperatures immediately below the melting temperature by means of differential scanning calorimetry.