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

摘要

~(13)C 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 shpae and symmetry match in the reorientational dynamics of the metal carbonyls is discussed.