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

Abstract

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.