Lanthanide-organic frameworks based on terphenyl-tetracarboxylate ligands: syntheses, structures, optical properties and selective sensing of nitro explosives

Three isostructural three-dimensional (3D) lanthanide-based metal-organic frameworks [Ln(2)L(H2L)(NMP)(2)]center dot H2O (Ln=Sm (1), Eu (2), Gd (3); H4L=1,1':4',1 ''-terphenyl-2',4,4 '',5'-tetracarboxylic acid; NMP=N-methyl-2-pyrrolidone) have been synthesized and structurally characterized. In 1-3, two Ln(3+) ions are doubly-bridged by two oxygen atoms of two carboxylate groups to form the dinuclear Ln(2)(O-coo(-))(2) unit. Each unit Ln(2)(O-coo(-))(2) links with four H2L2- ligands and four L4- ligands to lead to the 3D framework, which can be rationalized as a new trinodal 4,4,8-connected (4(4).6(2))(4(5).6)(4(12).6(16)) topological network by considering the dinuclear units as 8-connected nodes and L4-/H2L2- ligands as planar 4-connected nodes, respectively. 1 and 3 exhibit blue emission originated from the ligand with the emission maximum at 384 nm, while 2 shows intense characteristic red emission of Eu3+ ions and weak ligand-centered emission. Moreover, 2 has fluorescent quenching response towards the aromatic nitro compounds, especially for the 3,4-dinitrotoluene (3,4-DNT) with the linear Stern-Volmer relationship in the concentration range of 0-1 mM and the quenching constant (K-sv) of 2.084x10(3) M-1.