Isomorphous Co(ii) and Ni(ii) antiferromagnets based on mixed azide- and carboxylate-bridged chains: Metamagnetism and single-chain dynamics

Two isomorphous Co(ii) and Ni(ii) coordination polymers with azide and the 4-(4-pyridyl)benzoic acid N-oxide ligand (4,4-Hopybz) were synthesized, and structurally and magnetically characterized. They are formulated as [M(4,4-opybz)(N₃)(H₂O)]_n (M = Co, 1 and Ni, 2). The compounds consist of 2D coordination networks, in which 1D coordination chains with (μ-N₃)(μ-COO) bridges are interlinked by the 4,4-opybz spacers, and the structure also features intra- and interchain O-H⋯O hydrogen-bonding bridges between metal ions. Both compounds exhibit ferromagnetic interactions through the intrachain (μ-N₃)(μ- COO)(O-H⋯O) bridges and antiferromagnetic interactions through the interchain O-H⋯O bridges. The ferromagnetic chains are antiferromagnetically ordered, and the antiferromagnetic phases exhibit field-induced metamagnetic transition. It is found that 1 displays slow relaxation of magnetization, typical of single-chain magnets, while 2 does not. The difference emphasizes the great importance of large magnetic anisotropy for single-chain-magnet dynamics.