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)(N(3))(H(2)O) (M = Co, 1 and Ni, 2). The compounds consist of 2D coordination networks, in which 1D coordination chains with (μ-N(3))(μ-COO) bridges are interlinked by the 4,4-opybz spacers, and the structure also features intra- and interchain O-HO hydrogen-bonding bridges between metal ions. Both compounds exhibit ferromagnetic interactions through the intrachain (μ-N(3))(μ-COO)(O-HO) bridges and antiferromagnetic interactions through the interchain O-HO 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.