Targeted replacement: systematic studies of dodecanuclear {M III6Ln III6} coordination clusters (M = Cr, Co; Ln = Dy, Y)

Abstract

Three dodecanuclear 3d–4f coordination clusters, [Cr^III₆Ln^III₆(μ₃-OH)₈(tbdea)₆(C₆H₅COO)₁₆]·2H₂O (Ln = Dy (1), Y (2)) and [Co^III₆Dy^III₆(μ₃-OH)₈(nbdea)₆(m-CH₃C₆H₄COO)₁₆]·2H₂O·2CH₃CN (3), have been synthesized under solvothermal conditions and characterized. Single-crystal X-ray diffraction analysis revealed that all three compounds possess an analogous {M^III₆Ln^III₆} core (M = Cr, Co; Ln = Dy, Y) and dc magnetic susceptibility studies indicated that the magnetic exchange couplings between Dy^III ions are dominant antiferromagnetic, while the Cr^III–Dy^III interactions are weakly ferromagnetic. Furthermore, the ac magnetic susceptibility measurements showed that both Cr^III₆Dy^III₆ compound 1 and Co^IIi₆Dy^III₆ compound 3 containing highly anisotropic Dy^III ions displayed single-molecule magnetic (SMM) behavior with the energy barrier U_eff increasing from 12.8 K (for 1) to 20.8 K (for 3), indicating that weak 3d–4f exchange couplings enhance the QTM and reduce the energy barrier.