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

C-13 NMR measurements have been carried out on (CH3)-C-13-labeled Mn12O12-acetate in both powder and magnetically aligned samples at an applied magnetic field of 8.5 T. The four observed peak,, are assignable to the four distinct (CH3)-C-13 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 titled to the dipolar plus isotropic interactions and the Fermi-contact parts, and impaired electron spill 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. (C) 2002 Published by Elsevier Science Ltd.