Tetra- and Binuclear Complexes of Hydroxy-Rich Ligands: Supramolecular Structures, Stabilization of Unusual Water Clusters, and Magnetic Properties

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Abstract

Three tetranuclear complexes [Cu4(H2L1)4]·10H2O (1), [Ni4(H2O)3(H2L1)3(OH)]NO3·6H2O (2) and [Zn4(H2L1)4]·2MeOH·2H2O (3) and two binuclear complexes [Cu2(H3L1)2(NO3)2] (4) and [Cu2(H3L2)2Cl2](ClO4)2·2H2O (5) have been synthesized from two potentially pentadentate hydroxyl-rich ligands H4L1 and H3L2 (H4L1 = tris(hydroxymethyl)(2-hydroxybenzylamino)methane, and H3L2 = tris(hydroxymethyl)(2-pyridylamino) methane). X-ray analyses reveal that complexes 1, 2, and 3 have cubane core structures. For 1, ten lattice water molecules are linked by twelve hydrogen bonds, forming an extremely unusual adamantanoid (H2O)10 cluster, which is linked to two tetranuclear moieties by octadruple hydrogen bonds. For 2, four water dimers are bridged by two nitrates, giving a [(H2O)8(NO3)2]2- cluster. 4 has a bis(μ2-phenoxo)-bridged dicopper(II) structure with the binuclear species linked by multiple hydrogen bonds, affording a ladder-like structure. 5 has a bis(μ2-Cl)-bridged dicopper(II) structure with the binuclear moieties linked by π−π interactions and hydrogen bonds, affording a 2D network. In these complexes, the hydroxyl-rich ligands coordinate in dianionic, monoanionic or neutral forms, with one of the alkoxyl groups of each ligand left noncoordinated and open for intermolecular interactions, resulting in the stabilization of various water clusters and the formation of various supramolecular assemblies. Magnetic measurements reveal that, for 1 and 2, antiferromagnetic and ferromagnetic couplings coexist, thus resulting in interesting nonzero spin ground state. The ferromagnetic behavior of 1 can be ascribed to the nearly perpendicular arrangement of dx2−y2 magnetic orbitals of Cu(II) centers with the dihedral angle of 84.06(3)° between the Cu(II) equatorial planes. 4 shows a strong antiferromagnetic interaction. On the other hand, 5 shows a ferromagnetic interaction between copper(II) centers. Magneto-structural correlations have been discussed.

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