Self-assembly and characterization of copper 3,4-pyridinedicarboxylate complexes based on a variety of polynuclear hydroxo clusters

Self-assembly of copper(II) ion, 3,4-pyridinedicarboxylate (PDC), and 1,10-phenanthroline (phen) under basic conditions at 100 °C affords four PDC linked copper(II) complexes, [Cu4(μ2-OH)3(μ3-OH)(PDC)(phen)4]n·n(PDC)·11.5nH2O (1), [Cu4(μ2-OH)2(μ3-OH)2(PDC)(phen)4]n·n(PDC)· 11.5nH2O (2), [Cu8(μ2-OH)2(μ3-OH)6(PDC)2(phen)8]·2(PDC)·23H2O (3), and [Cu3.5(μ2-OH)3 (PDC)2(phen)]n (4). 1–4 are copper hydroxo complexes, and 1, 2 and 3 co-crystallized from the one-pot reaction. X-ray single crystal diffraction analyses indicate that complexes 1 and 2 are linkage isomers and contain tetranuclear copper cluster cores with different geometry, and that PDC links the cluster core to form a one-dimensional chain. Complex 3 is a discrete step-like octanuclear copper hydroxo cluster complex. The involvement of hydroxo and phen in the coordination makes some coordination sites of PDC idle, which leads to rich hydrogen bonds and π–π interactions in complexes 1, 2 and 3. Complex 4 contains two types of copper hydroxo cluster cores: chair-like tetranuclear and linear trinuclear units, and the cluster cores are linked by PDC to a double-layer metal–organic framework. Magnetic properties of 1, 3 and 4 were investigated. The results reveal that complexes 3 and 4 exhibit strong antiferromagnetic interactions whereas ferromagnetic coupling is predominant for complex 1. The magnetic properties are analyzed in connection with their structures.