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

The synthesis, structure, and magnetic properties of four Dy-III coordination compounds isolated as [Dy-2(LH2)(2)((2)-(1):(1)-Piv)]Cl2MeOHH(2)O (1), [Dy-4(LH)(2)((3)-OH)(2)(Piv)(4)(MeOH)(2)]4MeOH2H(2)O (2), [Dy-6(LH2)(3)(tfa)(3)(O3PtBu)(Cl)(3)]Cl(4)15.5H(2)O4MeOH5CHCl(3) (3) and [Dy-21(L)(7)(LH)(7)(tfa)(7)]Cl(7)15H(2)O7MeOH12CHCl(3) (4) are reported (Piv=pivalate, tfa=1,1,1-trifluoroacetylacetone, O3PtBu=tert-butylphosphonate). Among these, 3 displays an equilateral triangle topology with a side length of 9.541 angstrom 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 15K at zero bias field, but without exhibiting any maximum above 2K at frequencies up to 1400Hz. 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 2K, or there exists quantum tunneling of the magnetization (QTM).