Assembly of Lanthanide(III) Cubanes and Dimers with Single-Molecule Magnetism and Photoluminescence

Discrete lanthanide(III) tetranuclear cubane-like clusters seldom occur throughout the LnIII series and behave as single-molecule magnets (SMMs). Herein, a series of cubanes, [Ln4(μ3-OH)4(μ-tfa)4(hfa)4(phen)4] (1–9, Ln = La–Dy (except Pm), tfa = trifluoroacetate, hfa = hexafluoroacetylacetonate, phen = 1,10-phenanthroline), and dinuclear clusters, [Ln2(μ-OH)2(hfa)4(phen)2] (10–16, Ln = Tb–Lu), were synthesized and characterized. Two types of clusters were formed due to the change of preferred coordination geometry for lighter and heavier LnIII ions which favor nine-coordinated cubanes and eight-coordinated dimers, respectively. A magnetic study shows that 8-Tb4 and 9-Dy4 are ferromagnetically coupled and SMM in nature because of the larger Ln···Ln distance compared to other discrete cubanes. The anisotropic barriers, Ueff, of 9-Dy4 are determined to be 67.0 K. In addition, the photophysical properties of 6-Eu4, 8-Tb4, and 10-Tb2 owing to tfa, hfa, and phen sensitization and O–H quenching are discussed.