One-dimensional copper phosphonates containing μ-halide, μ-pyridyl N-oxide and phosphonate bridging ligands

This paper reports the syntheses and characterization of four copper phosphonates with chain structures based on (2-pyridyl-N-oxide)phosphonate, namely, [Cu2X2(C5H4NOPO3)2][Cu(H2O)6] · 2H2O [X = Cl (1), Br (2)] and CuX(C5H4NOPO3H) · H2O [X = Cl (3), Br (4)]. Compounds 1 and 2 are isostructural and show a chain structure where Cu(1) and Cu(2) are triply bridged by halide, oxygen donor of the pyridyl N-oxide and O–P–O group. The [Cu(H2O)6]2+ serves as a charge-balancing cation and locate between the chains together with the water molecules. Compounds 3 and 4 are also isostructural. In these cases, one of the three phosphonate oxygen atoms is protonated, thus leading to a neutral chain structure which is very similar to the anionic chains in compounds 1 and 2. Magnetic studies of compounds 1–4 reveal that antiferromagnetic interactions are mediated between the copper ions.