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, Cu(4)(μ(2)-OH)(3)(μ(3)-OH)(PDC)(phen)(4)·n(PDC)·11.5 nH2O (1), Cu(4)(μ(2)-OH)(2)(μ(3)-OH)(2)(PDC)(phen)(4)·n(PDC)· 11.5 nH(2)O (2), [Cu(8)(μ(2)-OH)(2)(μ(3)-OH)(6)(PDC)(2)(phen)(8)]·2(PDC)·23 H(2)O (3), and Cu(3.5)(μ(2)-OH)(3) (PDC)(2)(phen) (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.