13C NMR evidence for Fermi-contact interaction and spin delocalization on the ligands in the nanomagnet MN12O12-acetate

13C NMR measurements have been carried out on 13CH3-labeled Mn12O12-acetate in both powder and magnetically aligned samples at an applied magnetic field of 8.5 T. The four observed peaks are assignable to the four distinct 13CH3 moieties. The spectra were measured as a function of the orientation of the Zeeman field with respect to the easy axis in an aligned powder sample. The line positions were fitted to the dipolar plus isotropic interactions and the Fermi-contact parts, and unpaired electron spin density was calculated for each site. The results demonstrate significant spin density delocalization onto the acetate fragments and complement recent proton NMR and polarized neutron diffraction data on this system.