Hexanuclear 3d–4f Neutral Co^II₂Ln^III₄ Clusters: Synthesis, Structure, and Magnetism

The sequential reaction of the multisite coordination ligand 6,6′-{(2-(dimethylamino)­ethyl azanediyl)­bis­(methylene)}­bis­(2-methoxy-4-methylphenol) (LH2) with LnIII salts (Ln = Gd, Tb, Dy) and Co­(ClO4)2·6H2O in the presence of triethylamine and pivalic acid (pivH) in ambient conditions afforded a series of isostructural heterometallic hexanuclear CoII/LnIII complexes with the general formula [CoII2Ln4­(μ3-OH)4­(L)2(piv)8­(μ-OH2)]­·wCH3C­·xCH2Cl2­·yCH3OH­·zH2O (1: Ln = Gd, w = 5, x = 2, y = 0, z = 2; 2: Ln = Tb, w = 7, x = 4, y = 2, z = 0; 3: Ln = Dy; w = 4, x = 2, y = 2, z = 0). Compounds 1 and 3 crystallize in the monoclinic system, space group P21/n (Z = 4), while compound 2 crystallizes in P2/n (Z = 2). The hexanuclear core of the complexes comprises of a nonplanar arrangement of lanthanide ions bridged by two μ3-OH ligands. This tetranuclear motif is connected to the CoII ions by two μ3-OH ligands. The overall structure contains four interlinked incomplete cubic subunits (two CoIILnIII2O4 and two LnIII3O4) that are connected to each other by the sharing of two LnIII ions. The lanthanide centers are eight-coordinate (distorted trigonal-dodecahedron) and nine-coordinate (distorted monocapped square-antiprism), while the cobalt centers are six-coordinate (distorted octahedral). Magnetic measurement of the dysprosium analogue shows a slow magnetic relaxation.