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.