A series of tetranuclear-cluster-containing complexes based on pendent-arm macrocyclic ligand and different carboxylates: syntheses, structures, photoluminescence, and magnetic properties

Abstract

Eight new tetranuclear-cluster-containing compounds based on the carboxylate armed aza-macrocycle ligand, namely, [Co4(L)(Ac)2(H2O)4] (1), [Mn4(L)(Ac)2(H2O)4] (2), [Co8(L)2(L1)2(H2O)6]·H2O (3), [Zn8(L)2(L1)2(H2O)6]·H2O (4), [Co4(L)(L2)(H2O)2]·H2O (5), [Zn4(L)(L2)(H2O)2]·H2O (6), [Co4(L)(L3)(H2O)4]·H2O (7), and [Co2(L)0.5(L4)0.5(H2O)]·0.7H2O (8), where HAc = acetic acid, H6L = tetraacetic acid tetraaminodiphenol macrocyclic ligand, H2L1 = 1,3-benzenedicarboxylic acid, H2L2 = oxalic acid, H2L3 = fumaric acid and H2L4 = 1,6-hexanedioic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra and thermogravimetric analyses (TGA). Compounds 1 and 2 possess the isostructural tetranuclear structures, which are further extended into 2D supramolecular layers via intermolecular O–H⋯Ocarboxylate interactions. Compound 4 is isostructural with compound 3. In compound 3, the L1 anions linked the tetranuclear cobalt–oxygen clusters to form a chain structure. The chains are further connected by intermolecular O–H⋯Ocarboxylate hydrogen bonds to result in a 1D supramolecular double chain. Compounds 5 and 6 are isomorphous. Both 5 and 6 contain tetranuclear metal clusters. The tetranuclear metal clusters are bridged by L2 anions to yield infinite chain structures. Compound 7 displays an infinite chain structure based on tetranuclear cobalt–oxygen clusters. The neighboring chains are further extended into a 2D supramolecular sheet by intermolecular O–H⋯Ocarboxylate hydrogen bonds. Compound 8 shows a 1D zigzag chain structure constructed by tetranuclear cobalt–oxygen clusters and L4 anions. The variable-temperature (4–300 K) magnetic susceptibilities indicate that the tetranuclear metal unit in 2 exhibits antiferromagnetic as well as weak ferromagnetic exchange interactions, whereas in 1, 5, and 7 the exchange interactions are antiferromagnetic. Furthermore, the luminescent properties for compounds 4 and 6 have also been investigated.