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

Abstract

The sequential reaction of the multisite coordination ligand 6,6′-{(2-(dimethylamino)­ethyl azanediyl)­bis­(methylene)}­bis­(2-methoxy-4-methylphenol) (LH₂) with Ln^III 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 Co^II/Ln^III complexes with the general formula [Co^II₂Ln₄­(μ₃-OH)₄­(L)₂(piv)₈­(μ-OH₂)]­·<i>w</i>CH₃C­·<i>x</i>CH₂Cl₂­·<i>y</i>CH₃OH­·<i>z</i>H₂O (<b>1</b>: Ln = Gd, <i>w</i> = 5, <i>x</i> = 2, <i>y</i> = 0, <i>z</i> = 2; <b>2</b>: Ln = Tb, <i>w</i> = 7, <i>x</i> = 4, <i>y</i> = 2, <i>z</i> = 0; <b>3</b>: Ln = Dy; <i>w</i> = 4, <i>x</i> = 2, <i>y</i> = 2, <i>z</i> = 0). Compounds <b>1</b> and <b>3</b> crystallize in the monoclinic system, space group <i>P</i>2₁/<i>n</i> (<i>Z</i> = 4), while compound <b>2</b> crystallizes in <i>P</i>2/<i>n</i> (<i>Z</i> = 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 Co^II ions by two μ₃-OH ligands. The overall structure contains four interlinked incomplete cubic subunits (two Co^IILn^III₂O₄ and two Ln^III₃O₄) that are connected to each other by the sharing of two Ln^III 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