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

The synthesis, structure, and magnetic properties of four DyIII coordination compounds isolated as [Dy2 (LH2 )2 (μ2 -η1 :η1 -Piv)]Cl⋅2 MeOH⋅H2 O (1), [Dy4 (LH)2 (μ3 -OH)2 (Piv)4 (MeOH)2 ]⋅4 MeOH⋅2 H2 O (2), [Dy6 (LH2 )3 (tfa)3 (O3 PtBu)(Cl)3 ]Cl4 ⋅15.5 H2 O⋅4 MeOH⋅5 CHCl3 (3) and [Dy21 (L)7 (LH)7 (tfa)7 ]Cl7 ⋅15 H2 O⋅7 MeOH⋅12 CHCl3 (4) are reported (Piv=pivalate, tfa=1,1,1-trifluoroacetylacetone, O3 PtBu=tert-butylphosphonate). Among these, 3 displays an equilateral triangle topology with a side length of 9.541 Å and a rare pentagonal-bipyramidal Dy3+ 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 Dy3+ 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).