Intramolecular host-guest dynamics of FeCp(CO)(2)X (X= I and CH3) and Mo2Cp2(CO)(6) included in beta- or gamma-cyclodextrin

Variable-temperature C-13 CPMAS NMR spectra of the metal-carbonyl complexes FeCp(CO)(2)X (where X = I, CH3) and Mo2Cp2(CO)(6) included in beta- or gamma-cyclodextrin (CD) cavities were investigated in the temperature range 133 to 293 K. The motion of the guest molecule inside the CD can be detected by comparing these spectra with the static crystalline patterns of FeCp(CO)(2)I and Mo2Cp2(CO)(6). In the case of FeCp(CO)(2)CH3, solid-state plastic crystal behaviour is noted for the free guest; the molecular motion is further modified by inclusion within the CD cavity. The nature of the molecular motion found within the metal-carbonyl/CD adducts was shown to be dependent on the symmetry, size and orientation of the guest molecule within the host cavity. In the case of Mo2Cp2(CO)(6) included in gamma-CD, the two [MoCp(CO)(3)] ends of the dimer may be considered as separate dynamic entities: one half of the moiety within the CD cavity exhibits a greater freedom of motion, whereas the other end of the dimer is anchored. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).