The role of molecular shape and axial symmetry in the solid state molecular dynamics of metal carbonyl compounds included in cyclodextrin cavities

C-13 CP/MAS NMR spectra of the metal carbonyl complexes Cr(CO)(6), Fe(CO)(5) and Mn-2(CO)(10) included in beta- and gamma -cyclodextrin (CD) cavities have been studied in the temperature range 133 to 423 K. Cr(CO)(6) molecules reorient effectively isotropically within gamma -cyclodextrin, Fe(CO)(5) molecules in beta -cyclodextrin reorient effectively isotropically and show rapid axial-equatorial exchange, but Mn-2(CO)(10) in the super-cage defined by two gamma -cyclodextrin molecules shows MAS sidebands at lower temperatures indicative of a more restricted motion such as molecular gyration. The important role of guest and host molecular shape and symmetry match in the reorientational dynamics of the metal carbonyls is discussed.