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

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(H2O)] · 2H2O}n (L = bipy (1), bpa (2) and bpe (3)), {[M(pydco)(bpp)(H2O)] · 2H2O}n (M = Cu (4) and Ni (5)), [Ag2(pydco)]n (6) and [Ag2Cu(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 · H2O 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 [AgCO2]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 J1 = −4.59 cm−1 and J2 = −4.63 cm−1, respectively. Whereas 7 displays weak ferromagnetic interactions with J3 = 1.81 cm−1.