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

Discrete lanthanide(III) tetranuclear cubane-like clusters seldom occur throughout the Ln series and behave as single-molecule magnets (SMMs). Herein, a series of cubanes, [Ln(μ-OH)(μ-tfa)(hfa)(phen)] (1-9, Ln = La-Dy (except Pm), tfa = trifluoroacetate, hfa = hexafluoroacetylacetonate, phen = 1,10-phenanthroline), and dinuclear clusters, [Ln(μ-OH)(hfa)(phen)] (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 Ln ions which favor nine-coordinated cubanes and eight-coordinated dimers, respectively. A magnetic study shows that 8-Tb and 9-Dy are ferromagnetically coupled and SMM in nature because of the larger Ln···Ln distance compared to other discrete cubanes. The anisotropic barriers, U, of 9-Dy are determined to be 67.0 K. In addition, the photophysical properties of 6-Eu, 8-Tb, and 10-Tb owing to tfa, hfa, and phen sensitization and O-H quenching are discussed.