SMM behaviour in a {CoIII4CoII2DyIII2} complex: Co(II)-based thermal barrier and Dy(III) spectator role
Lara Martinez1, David Hunger2, Carlos Cruz3,4
1Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE (CONICET), Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, C1428EHA Buenos Aires, Argentina. albores@qi.fcen.uba.ar.
None:
We report the synthesis, structure, and magnetic properties of a novel Co/Dy heterometallic complex, [CoIII4CoII2DyIII2(tea)4(CH3COO)4(OH)2(NO3)4]·2H2O (1), the first structurally characterized example of a mixed-valent {CoIII4CoII2DyIII2} motif. It comprises two butterfly-like {CoIII2CoIIDyIII} units linked by carboxylate and alkoxide bridges. X-ray diffraction shows unique Dy(III) and Co(II) sites, with Dy(III) nine-coordinated and Co(II) in a rhombic tetrahedral geometry. Magnetic data and quantum chemical calculations reveal weak Co(II)-Co(II) antiferromagnetic exchange, negligible Co(II)-Dy(III) interactions, and moderate Co(II) zero-field splitting (D ≈ 12-20 cm-1), which drives single-molecule magnet behavior below 14 K. AC studies indicate multiple tunneling pathways and an Orbach barrier (Ueff ≈ 65 cm-1) arising from Co(II), while Dy(III) ions remain largely magnetically decoupled.
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