New examples of low-dimensional metal-pydco complexes: Syntheses, structures and magnetic properties

Abstract

This work presents a systematic investigation on coordination chemistry of a novel pyridine-2,6-dicarboxylic acid N-oxide (pydco), and also reveals the significant function of supramolecular interactions in dominating the resultant crystalline nets. Assemblies of pydco with transition-metal ions under similar conditions yield a series of polymers in the absence/presence of the organonitrogen ligands {[Cu(pydco)(L) 0.5(H 2O)] · 2H 2O} n (L = bipy ( 1), bpa ( 2) and bpe ( 3)), {[M(pydco)(bpp)(H 2O)] · 2H 2O} n (M = Cu ( 4) and Ni ( 5)), [Ag 2(pydco)] n ( 6) and [Ag 2Cu(pydco) 2] n ( 7) (bipy = 4,4′-bipyridine, bpa = 1,2-bis(4-pyridyl)ethane, bpe = 1,2-bis(4-pyridyl)ethene, bpp = 1,3–bis(4-pyridyl)propane). 1– 5 feature different structural characteristics, although they exhibit analogous chain networks. Remarkably, extended architectures are further constructed with the aid of weak interactions. Reaction of pydco with AgAc yields a 2-D polymer 6, which was reported in our recent Communication. A mixed-metal coordination polymer 7 was obtained by the self-assembly of AgAc, Cu(Ac) 2 · H 2O and pydco. In 7, two left- and right-hand helical chains are constructed by carboxylic groups of pydco and Cu centers, which are further connected by [AgCO 2] 2 cores into a 2-D network. Structural evolution under the co-ligand intervention in this series of compounds, as well as the general coordination rule of pydco, has been further discussed. Furthermore, variable temperature magnetic properties of 1, 3 and 7 are also studied. The magnetic measurements of 1 and 3 reveal the existence of weak antiferromagnetic interactions with J 1 = −4.59 cm −1 and J 2 = −4.63 cm −1, respectively. Whereas 7 displays weak ferromagnetic interactions with J 3 = 1.81 cm −1.