Synthesis, structures, and magnetism of copper(II) and manganese(II) coordination polymers with azide and pyridylbenzoates

Three transition-metal coordination polymers with azide and/or carboxylate bridges have been synthesized from 4-(3-pyridyl)benzoic acid (4,3-Hpybz) and 4-(4-pyridyl)benzoic acid (4,4-Hpybz) and characterized by X-ray crystallography and magnetic measurements. Compound 1, [Cu(4,3-pybz)(N₃)] _n, consists of 2D coordination networks in which the uniform chains with (μ-EO-N₃)(μ-COO) double bridges are cross-linked by the 4,3-pybz ligands. Compound 2, [Cu₂(4,4-pybz)₃(N ₃)]_n•3nH₂O, consists of 2-fold interpenetrated 3D coordination networks with the α-Po topology, in which the six-connected dinuclear motifs with mixed (μ-EO-N₃)(μ-COO) ₂ (EO = end-on) triple bridges are linked by the 4,4-pybz spacers. Compound 3, [Mn(4,4-pybz)(N₃)(H₂O)₂] _n, contains 2D manganese(II) coordination networks in which the chains with single μ-EE-N₃ bridges (EE = end-to-end) are interlinked by the 4,4-pybz ligands, and the structure also features a 2D hydrogen-bonded network in which Mn^II ions are linked by double triatomic bridges, (μ-EE-N₃)(O-H•••N) and (O-H•••O)₂. Magnetic studies indicated that the mixed azide and carboxylate bridges in 1 and 2 induce ferromagnetic coupling between Cu^II ions and that 3 features antiferromagnetic coupling through the EE-azide bridge. In addition, compound 1 exhibits antiferromagnetic ordering below 6.2 K and behaves as a field-induced metamagnet. A magnetostructural survey indicates a general trend that the ferromagnetic coupling through the mixed bridges decreases as the Cu-N-Cu angle increases.