Elucidation of1H NMR Paramagnetic Features of Heterotrimetallic Lanthanide(III)/Manganese(III) 12-MC-4 Complexes

The paramagnetic one-dimensional1H NMR spectra of twelve LnIIINaI(OAc)4[12-MCMnIII(N)shi-4] complexes, where LnIIIis PrIII-YbIII(except PmIII) and YIII, are reported. Their solid-state isostructural nature is confirmed in methanol-d4solution, as a similar pattern in the1H NMR spectra is observed along the series. Notably, a relatively well-resolved spectrum is reported for the GdIIIcomplex. 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-YbIIIcomplexes, the pseudo-contact contributions are typically 1 order of magnitude higher than the Fermi contact contributions; however, for the GdIIIcomplex, 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 NaIcation 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.