SOLID-STATE C-13 CP-MAS NMR-SPECTRA OF IRON (ALKYNE) CARBONYL-COMPOUNDS

The solid state ¹³C NMR spectra of a series of iron (alkyne) carbonyl complexes, enriched in ¹³C at the carbonyl groups, have been obtained using ¹³C-{¹H} cross-polarisation (CP) and slow magic angle spinning (MAS). In general, more resonances are observed from the solid state than from samples in solution; this may be due either to crystal packing effects lifting the degeneracy of certain signals or to a slowing of carbonyl fluxionality in the solid state. The intensities of the spinning side bands in the ¹³C spectra have been used to derive values for the components of the ¹³C shielding tensor. The component of the shielding tensor assigned to the CO bond axis (σ₃₃) is sensitive to the bonding of the CO group, i.e. whether it is a terminal or asymmetrically bridging group.