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

Abstract

13C CP/MAS NMR spectra of the metal carbonyl complexes Cr(CO)6, Fe(CO)5 and Mn2(CO)10 included in β- and γ-cyclodextrin (CD) cavities have been studied in the temperature range 133 to 423 K. Cr(CO)6 molecules reorient effectively isotropically within γ-cyclodextrin, Fe(CO)5 molecules in β-cyclodextrin reorient effectively isotropically and show rapid axial–equatorial exchange, but Mn2(CO)10 in the super-cage defined by two γ-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.