New Dioximes as Bridging Ligands in 3d/4f-Metal Cluster Chemistry: One-Dimensional Chains of Ferromagnetically Coupled {Cu(6)Ln(2)} Clusters Bearing Acenaphthenequinone Dioxime and Exhibiting Magnetocaloric Properties.

The employment of the tetradentate ligand acenaphthenequinone dioxime (acndH(2)) for a first time in heterometallic Cu-II/Ln(II) (Ln = Gd and Dy) chemistry has afforded the one-dimensional coordination polymers [Cu6Gd2(acnd)(6)(acridH)(6)(MeOH)(6)](n), (1) and [Cu6Dy2(acnd)(6)(acndH)(6)(MeOH)(2)](n) (2), which consist of repeating {Cu(6)Ln(2)} clusters that are intermolecularly linked to each other through the oximate groups of two eta(2):eta(1):eta(1):eta(3) acnd(2)- ligands. The [Cu(6)Ln(2)(mu(3)-NO)(6)(mu-NO)(8)](4+). core is unprecedented in heterometallic cluster chemistry and comprises two symmetry-related {Cu(3)Ln} subunits, each with a distorted trigonal pyramidal topology. Magnetic susceptibility studies revealed the presence of predominant ferromagnetic exchange interactions within the {Cu(3)Ln} subunits and weak antiferromagnetic interactions between them. As a result, the magnetic and magnetocaloric properties of the {Cu6Gd2} compound could be rationalized in terms of two weakly coupled S = 5 spins that yield a magnetic entropy change of -Delta S-m = 11.8 J kg(-1) K-1 at T = 1.6 K for mu(0)Delta H = 7 T.