Synthesis, crystal structures and magnetism of a series of heptanuclear rare-earth-centered trigonal prism clusters

A series of heptanuclear rare-earth-centered trigonal prism clusters [LnCu₆(μ-OH)₃(HL)₂(L)₄] ·(ClO₄)₂·25H₂O (Ln = La-Ho and Y; H₂L = iminodiacetic acid) was synthesized and their crystal structures were determined by X-ray diffraction. The rare-earth center and the copper ions are bridged by three μ₃-OH and six μ₂-O moieties from the carboxyl groups of six different ligands. The rare earth ion is nine-coordinate and the coordination polyhedron is an unusual, highly symmetrical tricapped trigonal prism (C_3h). The cluster has an interesting, highly symmetrical eclipsed structure (C_3h) which utilizes the central rare earth cation as a template. The temperature-dependence of the magnetic susceptibility of the cluster series was investigated and was found to vary with the central rare-earth ions. The magnitude of the antiferromagnetic interaction constants J between Cu²⁺ ions in [LaCu₆] and [YCu₆] were compared and estimated to be -24 cm^-1 and -7 cm^-1, respectively, indicating a significant effect of the central diamagnetic ions.