Co-ligand-directed structural and magnetic diversities in an anisotropic CoII–triazolate system

Abstract

Three novel 3,5-diamino-1,2,4-triazole (Hdatrz)-based Co^II coordination complexes, [Co(Hdatrz)_0.5(H₂O)₂(btec)_0.5]_n (1), {[Co(Hdatrz)(Hbtc)]·H₂O}_n (2) and [Co₂(datrz)₂(nb)₂]_n (3) (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, H₃btc = 1,3,5-benzenetricarboxylic acid and Hnb = 4-nitrobenzoic acid), were synthesized by incorporating different carboxylate-containing co-ligands and then were structurally and magnetically characterized. Complex 1 is a 3D pillared-layer framework with corrugated Co^II-btec⁴⁻ layers supported by neutral μ₂-N1, N4–Hdatrz ligands. In contrast, the other two complexes are chiral (4, 4)- and racemic (4, 8²)-topological layers with asymmetric μ₂-N1, N4–Hdatrz-bridged helical chains extended by bis-monodentate Hbtc²⁻ ligands for 2 and with a μ₃-N1, N2, N4-datrz⁻ aggregated Shastry–Sutherland magnetic layer for 3. More interestingly, different magnetic phenomena with a field-induced metamagnetic transition from antiferromagnetic ordering to a ferromagnetic state for 1, spin-canted antiferromagnetism with a T_N lower than 2.0 K for 2, as well as the coexistence of spin frustration and spin–flop transitions for 3 were observed, which, significantly, are governed by the local low-dimensional magnetic motifs mediated by the carboxylate and/or triazolate heterobridges in the anisotropic Co^II–triazolate system.