Assembly of metal coordination framework, [MII(C5O5)(dpe)], with a 2D bi-layer architecture: Thermal stability and magnetic properties (M = Mn, Fe, Cd and Co; dpe = 1,2-bis(4-pyridyl)ethane)

A series of coordination polymers, [M(C5O5)(dpe)] (M = Mn 1, Fe 2, Cd 3 and Co 4; dpe = 1,2-bis(4-pyridyl)ethane) with a 2D metal–organic framework (MOF) has been synthesized and characterized by single-crystal X-ray diffraction studies. Structural determination reveals that compounds 1–4 are isostructural and possess a 2D brick-wall-like layered framework with a rectangle grid as the basic building unit through the connectivity of metal ions with μ3-, μ4-croconates and anti-dpe ligands. Two 2D layers are then cross-linkaged by gauche-dpe ligands to complete a 2D bi-layered MOF and then extended to a 3D supramolecular architecture through π–π and C–H⋯O interactions between the croconate and pyridyl rings of dpe, which exhibit high thermo-stability and keep their crystalline forms up to 350 °C. The magnetic exchange coupling between the metal centers for compounds 1, 2 and 4 was analyzed and based on the Curie–Weiss expression and a binuclear magnetic model. The negative values of the Weiss constant and the magnetic exchange coupling constant indicate the antiferromagnetic nature between the metal ions via the bridges of bis-bidentate adjacent μ3-croconate ligands.

Graphical abstractA series of metal coordination solids, [M(dpe)(C5O5)] (M = Mn 1, Fe 2, Cd 3 and Co 4), have been synthesized and structurally characterized. Their 2D bi-layer MOFs are thermally stable and constructed by the cross-linkage of two brick-wall-like layers through the bridges of gauche-dpe ligands. The magnetic studies reveal a weak antiferromagnetic interaction via μ3-croconato bridges for 1, 2 and 3.Figure optionsDownload full-size imageDownload as PowerPoint slide