Probing Jahn-Teller distortions in Mn(acac)₃ through paramagnetic interactions in solid-state MAS NMR

The structural and electronic properties of solid coordination compounds are of great interest in a wide variety of applications. The sensitivity of solid-state NMR to local structural environments in the presence of a transition metal with unpaired spins is demonstrated through ¹³C and ¹H MAS NMR spectra of tris(acetylacetonato)manganese (III), Mn(acac)₃. The spectral assignment is established using a combination of density-functional theory and experimental NMR methods. An analysis of the spin-density distribution throughout the ligands as probed by NMR provides an understanding of the molecular electronic structure. The paramagnetic interaction enhances the spectral resolution and offers the possibility of using these spectra as structural fingerprints. The unique character of Mn(acac)₃ to manifest various degrees of Jahn-Teller distortions allows for a discussion of the relation between the electron occupancy, crystal structure, and ¹³C NMR peak shifts.