Two 3D metal–organic frameworks with different topologies, thermal stabilities and magnetic properties

Abstract

Two novel 3D metal–organic frameworks, [ML]_n (M = Co, 1; Mn, 2) were successfully prepared in solvothermal conditions using 3,3′-dimethoxy-4,4′-biphenyldicarboxylic acid (H₂L) as the ligand. X-Ray crystallography analysis reveals that MOF 1 crystallizes in the monoclinic system, space group P2₁/c in contrast to MOF 2 in the tetragonal system, space group I. MOF 1 contains an elongated [CoO₆] octahedron with two bound methoxy groups in the trans position, whereas MOF 2 has a compressed [MnO₆] octahedron with two coordinated methoxy groups in the cis arrangement. The ligand L shows a novel bis(tridentate) bridging coordination mode. MOF 1 exhibits a 3D framework with CdSO₄ (cds) topology consisting of two different nodes and good thermal stability (313 °C). MOF 2 is a doubly interpenetrated 3D α-Po framework with a higher thermal stability (368 °C). The study of magnetic properties in the temperature range of 1.8–300 K shows the occurrence of weak ferromagnetic interactions (J = 0.15 K) between the high-spin Co(II) ions in 1, but a weak antiferromagnetic coupling (J = −0.15 cm⁻¹) between Mn(II) ions in 2 due to the syn-anti carboxylate bridge.