The employment of the tetradentate ligand acenaphthenequinone dioxime (acndH2) for a first time in heterometallic CuII/LnIII (Ln = Gd and Dy) chemistry has afforded the one-dimensional coordination polymers [Cu6Gd2(acnd)6(acndH)6(MeOH)6]n (1) and [Cu6Dy2(acnd)6(acndH)6(MeOH)2]n (2), which consist of repeating {Cu6Ln2} clusters that are intermolecularly linked to each other through the oximate groups of two η2:η1:η1:μ3 acnd2– ligands. The [Cu6Ln2(μ3-NO)6(μ-NO)8]4+ core is unprecedented in heterometallic cluster chemistry and comprises two symmetry-related {Cu3Ln} subunits, each with a distorted trigonal pyramidal topology. Magnetic susceptibility studies revealed the presence of predominant ferromagnetic exchange interactions within the {Cu3Ln} subunits and weak antiferromagnetic interactions between them. As a result, the magnetic and magnetocaloric properties of the {Cu6Gd2}n …