Three 3D LnIII-MOFs based on a nitro-functionalized biphenyltricarboxylate ligand: syntheses, structures, and magnetic properties

Abstract

Three 3D lanthanide metal–organic frameworks (Ln-MOFs), [Pr₄(L)₄(H₂O)₈]·10H₂O (1), [Gd(L)(CH₃COOH)_0.5]·0.5H₂O (2), and [Dy(L)(H₂O)₂]·H₂O (3), H₃L = biphenyl-3′-nitro-3,4′,5-tricarboxylic acid, have been synthesized by solvothermal methods and their structures and magnetic properties were fully characterized. The Pr-MOF (1) contains unique linear-like tetranuclear clusters with triple and double carboxylate bridges. The tetranuclear clusters are cross-linked by L backbones to form a 3D framework, and it represents a rare (3,3,12)-connected net with the point symbol (4³)(4³)(4²¹·6²⁵·8¹⁸·10²). The Gd-MOF (2) is a layer-pillared 3D framework in which the layers with (μ-COO)₂(μ₂-O_carboxylate) triple bridges and single carboxylate bridges are interlinked by the L ligands. The Dy-MOF (3) is constructed from 1D uniform chain units with (μ-COO)₂ double bridges. Adjacent chains are connected by the L ligands into a 3D framework. Magnetic investigations on these MOFs have been carried out and revealed that the different carboxylate bridges are antiferromagnetic in the Pr-MOF (1) and Dy-MOF (3) but ferromagnetic in the Gd-MOF (2). Furthermore, the Dy-MOF (3) also shows slow magnetic relaxation behaviors under a zero dc field.