Hydrothermal syntheses, crystal structures and magnetic properties of four Mn(ii) and Co(ii) coordination polymers generated from new carboxylate-introduced 1,2,3-triazole ligands

Abstract

A new carboxylate-introduced 1,2,3-triazole, 1-(3,5-dicarboxyphenyl)-4-carboxy-1H-1,2,3-triazole (H₃dcpct), was synthesized by 1,3-dipolar cycloaddition of a terminal alkyne to azide in the presence of a Cu(II) salt. Hydrothermal reaction of H₃dcpct and Mn(NO₃)₂·6H₂O or Co(NO₃)₂·6H₂O in different NaOH/H₃dcpct molar ratios afforded four new coordination polymers [Mn(dcpt)(H₂O)₂]·0.25H₂O 1, [Mn(dcpt)(H₂O)] 2, [Co(dcpt)(H₂O)₂]·H₂O 3 and [Co(H₂O)₆][Co₂(dcpct)₂(H₂O)₆]·2H₂O 4 (H₂dcpt = 1-(3,5-dicarboxyphenyl)-1H-1,2,3-triazole). The in situ hydrothermal decarboxylation of H₃dcpct into H₂dcpt in 1–3 was found and its possible mechanism is proposed. In 1 and 3, dcpt²⁻ ligands bridge Mn(II) and Co(II) ions, respectively, to give two similar 2D layered structures with a (6,3)-connected network topology. Polymer 2 displays a whole achiral 3D open framework with both chiral and achiral channels in the same direction and possesses an unprecedented (3,6)-connected (4·8²)(4²·8¹²·10) network topology. The structure of 4 features a 1D chained net, in which no decarboxylation occurred. Variable-temperature magnetic susceptibility data show that 1 exhibits a weak ferromagnetic interaction and 2 manifests an overall antiferromagnetic interaction between their respective Mn(II) ions, while 3 and 4 display an antiferromagnetic interaction between Co(II) ions and/or spin-orbital coupling. The thermal stabilities of all obtained polymers have also been examined.