SYNTHESIS AND STRUCTURE OF DINUCLEAR COPPER(II) COMPLEXES OF A NOVEL HEXAAZA MACROCYCLE CONTAINING BRIDGING OXALATE AND ACETATE IONS

Non-template Schiff base [2 + 2] condensation of pyridine-2,6-dicarbaldehyde with 1,4-diamino-2-butyne yields the hexaazamacrocyclic ligand 1, which is converted to 2 by NaBH4 reduction of the imino groups. Two dinuclear copper(II) complexes of 2 containing oxalate and acetate ions, [(2)Cu-2(mu-C2O4)](BPh(4))(2) (3) and [(2)Cu-2(mu-CH3CO2) (OH2)](PF6)(2.25)-(NO3)(0.75) (4), were characterized by X-ray crystallography. The oxalate ligand in 3 forms a (mu eta(4):eta(4)) bridge between the copper atoms. Compound 4 contains a syn-anti-bridging acetate ion. The Cu-Cu distances are 5.315 Angstrom in 3 and 4.746 Angstrom in 4, respectively. Oxalate can be separated from other carboxylates in aqueous solution by selective binding to the[(2)Cu-2] unit and precipitation of 3.