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

Abstract

The synthesis, structure, and magnetic properties of four Dy^III 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).