New metalloligands suitable for the construction of polynuclear complexes and coordination polymers with exposed metal sites

New macrocyclic oxamide complexes suitable for being used as metalloligands to link metal ions were designed. Six coordination compounds containing a member of the new metalloligands as the bridging ligand were prepared. X-ray single crystal analysis revealed that the six compounds include a dodecanuclear structure, three 1D helical chainlike coordination polymers and two 2D layered coordination polymers. All of the nickel centres of the metalloligands in the six compounds are exposed on both sides of the corresponding square coordination planes, and all the bonds (Ni-N) formed by the open metal sites are significantly short (ranging from 1.848 to 1.888 angstrom). Thermogravimetric analysis of four of the six compounds showed that their thermal stabilities differ to a considerable extent and that the Na+-containing dodecanuclear structure, which began to decompose at ca. 400 degrees C, has the highest thermal stability.