New Dioximes as Bridging Ligands in 3d/4f-Metal Cluster Chemistry: One-Dimensional Chains of Ferromagnetically Coupled {Cu6Ln2} Clusters Bearing Acenaphthenequinone Dioxime and Exhibiting Magnetocaloric Properties

The employment of the tetradentate ligand acenaphthenequinone dioxime (acndH) for a first time in heterometallic Cu/Ln (Ln = Gd and Dy) chemistry has afforded the one-dimensional coordination polymers [CuGd(acnd)(acndH)(MeOH)] (1) and [CuDy(acnd)(acndH)(MeOH)] (2), which consist of repeating {CuLn} clusters that are intermolecularly linked to each other through the oximate groups of two ?:?:?:? acnd ligands. The [CuLn(?-NO)(?-NO)] core is unprecedented in heterometallic cluster chemistry and comprises two symmetry-related {CuLn} subunits, each with a distorted trigonal pyramidal topology. Magnetic susceptibility studies revealed the presence of predominant ferromagnetic exchange interactions within the {CuLn} subunits and weak antiferromagnetic interactions between them. As a result, the magnetic and magnetocaloric properties of the {CuGd} compound could be rationalized in terms of two weakly coupled S = 5 spins that yield a magnetic entropy change of -?S = 11.8 J kg K at T = 1.6 K for ??H = 7 T.