Symmetry-related [Ln~(III) _6Mn~(III) _(12)] clusters toward single-molecule magnets and cryogenic magnetic refrigerants

摘要

A family of high-nuclearity [Ln~(III) _6Mn ~(III) _(12)] (Ln = Gd, Tb) nanomagnets has been synthesized, of which two are in D_2 molecular symmetry and the other two are in C_1 symmetry. X-ray crystallography shows that each of them contains a similar {Mn~(III) _8O_(13)} unit, four marginal Mn~(III) ions, and two linear {Ln~(III) 3} units with parallel or perpendicular orientation for high- and low-symmetry cores, respectively. For [Gd~(III) _6Mn~(III) _(12)], the distinct spins of the {Mn~(III) _8O_(13)} unit lead to different spin ground states (S_T = 23 for the high-symmetry one and S_T = 16 for the low-symmetry one), and significant magnetocaloric effects are observed in a wide temperature range [full width at half-maximum (FWHM) of -ΔS_m > 18 K] that can maximizes the refrigerant capacity, which may be attributed to the ferromagnetic interactions. By replacement of isotropic Gd~(III) with anisotropic Tb~(III), they behave as single-molecule magnets, with the high-symmetry one possessing a larger effective barrier (36.6 K) than the low-symmetry one (19.6 K).