Elucidation of 1H NMR Paramagnetic Features of Heterotrimetallic Lanthanide(III)/Manganese(III) 12-MC-4 Complexes.

ABSTRACT

The paramagnetic one-dimensional 1H NMR spectra of twelve LnIIINaI(OAc)4[12-MCMnIII(N)shi-4] complexes, where LnIII is PrIII-YbIII (except PmIII) and YIII, are reported. Their solid-state isostructural nature is confirmed in methanol-d4 solution, as a similar pattern in the 1H NMR spectra is observed along the series. Notably, a relatively well-resolved spectrum is reported for the GdIII complex. The chemical shift data are analyzed using the "all lanthanides" method, and the Fermi contact and pseudo-contact contributions are calculated for the lanthanide-induced shift (LIS). For the TbIII-YbIII complexes, the pseudo-contact contributions are typically 1 order of magnitude higher than the Fermi contact contributions; however, for the GdIII complex, the Fermi contact is the main contribution to the paramagnetic chemical shift. For the methyl protons of the axial acetate (-OAc) ligands, the LIS is opposite in sign, with respect to that of the aromatic salicylhydroximate (shi3-) protons, because of structural rearrangements that occur upon dissociation of the NaI cation in solution. The calculated crystal field parameters (BLn) for the TbIII (360 cm-1), DyIII (250 cm-1), HoIII (380 cm-1), ErIII (410 cm-1), TmIII (620 cm-1), and YbIII (380 cm-1) complexes are not constant, likely as a consequence of the inaccuracy of the Bleaney's constants and, to a smaller extent, the small structural changes that occur in solution. Overall, the metallacrown scaffold retains structural integrity and similarity in solution for the entire series; however, small structural features, which do not affect the overall similarity, do likely occur.