Novel three-dimensional metal-azide network induced by a bipyridine-based zwitterionic monocarboxylate ligand: Structures and magnetism

The 4,4′-bipyridine-based zwitterionic monocarboxylate ligand, 4,4′-dipyridinio-1-acetate (L), is used as coligand to construct novel magnetic coordination polymers with mixed azide and carboxylate bridges. Two compounds, [Co₂(L)₂(N₃)₄(H ₂O)] 4H₂O (1) and [Mn₆(L)₄(N ₃)₁₂(H₂O)] 5H₂O (2), have been structurally and magnetically characterized. Compound 1 consists of one-dimensional (1D) coordination chains in which the unprecedented binuclear motifs with mixed (μ-EO-N₃)(μ-COO)₂ (EO = end-on) triple bridges are cross-linked by the 4,4′-dipyridinium-N-methylene spacers. In compound 2, the azide anions link the metal ions into a very complicated three-dimensional (3D) network with unprecedented topology, and the zwitterionic coligand is embedded in and serves as additional supports for the 3D network. Magnetic studies reveal that the mixed (μ-EO-N ₃)(μ-COO)₂ triple bridges transmit ferromagnetic coupling in the Co(II) compound, and the overall antiferromagnetic interactions exist in the Mn(II) compound.