Homometallic Dy Complexes of Varying Nuclearity from 2 to 21: Synthesis, Structure, and Magnetism.

The synthesis, structure, and magnetic properties of four Dy coordination compounds isolated as [Dy (LH ) (μ -η :η -Piv)]Cl⋅2 MeOH⋅H O (1), [Dy (LH) (μ -OH) (Piv) (MeOH) ]⋅4 MeOH⋅2 H O (2), [Dy (LH ) (tfa) (O PtBu)(Cl) ]Cl ⋅15.5 H O⋅4 MeOH⋅5 CHCl (3) and [Dy (L) (LH) (tfa) ]Cl ⋅15 H O⋅7 MeOH⋅12 CHCl (4) are reported (Piv=pivalate, tfa=1,1,1-trifluoroacetylacetone, O PtBu=tert-butylphosphonate). Among these, 3 displays an equilateral triangle topology with a side length of 9.541 Å and a rare pentagonal-bipyramidal Dy environment, whereas complex 4 exhibits a single-stranded nanowheel structure with the highest nuclearity known for a homometallic lanthanide cluster structure. A tentative model of the dc magnetic susceptibility and the low-temperature magnetization of compounds 1 and 2 indicates that the former exhibits weak ferromagnetic intramolecular exchange interaction between the Dy ions, whereas in the latter both intramolecular ferromagnetic and antiferromagnetic magnetic exchange interactions are present. Compounds 1, 3, and 4 exhibit frequency-dependent ac signals below 15 K at zero bias field, but without exhibiting any maximum above 2 K at frequencies up to 1400 Hz. The observed slow relaxation of the magnetization suggests that these compounds could exhibit single molecule magnet (SMM) behavior with either a thermal energy barrier for the reversal of the magnetization that is not high enough to block the magnetization above 2 K, or there exists quantum tunneling of the magnetization (QTM).