Heptanuclear lanthanide [Ln_7] clusters: from blue-emitting solution-stable complexes to hybrid clusters?

摘要

The use of LH_3 (2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol) and aibH (2-amino-isobutyric acid) in 4f chemistry has led to the isolation of eight new isostructural lanthanide complexes. More specifically, the reaction of the corresponding lanthanide nitrate salt with LH3 and aibH in MeOH, under solvothermal conditions in the presence of NEt_3, led to the isolation and characterization of seven complexes with the general formulae [Ln_7~(III)(OH)_2(L’)_9(aib)]·4MeOH (Ln = Gd, 1·4MeOH; Tb, 2·4MeOH; Dy, 3·4MeOH; Ho, 4·4MeOH; Er, 5·4MeOH; Tm, 6·4MeOH; Yb, 7·4MeOH L’ = the dianion of the Schiff base between naphthalene aldehyde and 2-amino-isobutyric acid). Furthermore, the isostructural YIII analogue, cluster [Y_7~(III)(OH)_2(L’)_9(aib)]·4MeOH (8·4MeOH), was synthesized in a similar manner to 1–7. The structure of all eight clusters describes a distorted [M_6~(III)] octahedron which encapsulates a seventh M~(III) ion in an off-centre fashion. Dc magnetic susceptibility studies in the 5–300 K range for complexes 1–7 reveal the presence of dominant antiferromagnetic exchange interactions within the metallic clusters as evidenced by the negative Weiss constant, θ, while ac magnetic susceptibility measurements show temperature and frequency dependent out-of-phase signals for the [Dy_7~(III)] analogue (3·4MeOH), suggesting potential single molecule magnetism character. Furthermore, for complex 1, simulation of its dc magnetic susceptibility data yielded very weak antiferromagnetic interactions within the metallic centres. Solid-state emission studies for all 1–8 clusters display ligand-based emission, while extended 1D and 2D NMR studies for 8·4MeOH reveal that the species retain their structural integrity in solution. In addition, TGA measurements for 1, 3 and 7 revealed excellent thermal stability up to 340 °C for the clusters.