Versatility of the methyl-bipyrimidine-N-oxide ligand for the design of lanthanide single-molecule magnets.

A library of ten complexes, [Yb2(hfac)6(L)] (1), [Yb6(hfac)14(OH)4(L)2] (2), [Dy(hfac)3(L)]2·C2H4Cl2 ((3)·C2H4Cl2), [Dy(hfac)3(L)]2[Dy(hfac)3(H2O)2] (4), [Dy6(hfac)14(OH)4(L)2] (5), [Yb(tta)3(L)] (6) and [Ln2(hfc)6(L)] (Ln = Dy ((-)7, (+)7) and Yb ((-)8, (+)8)) (where hfac- = 1,1,1,5,5,5-hexafluoroacetylacetonate, tta- = 2-thenoyltrifluoroacetylacetonate, hfc- = 3-(heptafluoropropylhydroxymethylene-(±)-camphorate and L = 4-methylbipyrimidine-2-N-oxide ligand)) were isolated and characterized by single crystal and powder X-ray diffraction. All the Yb(iii) based-complexes demonstrate a slow relaxation of the magnetization under an applied DC field, which occurs through a Raman process and an additional Orbach process for 6. The two Dy(iii) dinuclear complexes 3 and (±)7 display slow magnetic relaxation in a zero applied DC field, whereas complex 4, which is similar to 3 with co-crystallization of Dy(hfac)3(H2O)2, presents only a field-induced slow magnetic relaxation. Multi-field-induced single-molecule magnet (SMM) behaviour was observed for (+)7, while this was not the case for the Yb(iii) analogue (+)8.