Three sra topological lanthanide–organic frameworks built from 2,2′-dimethoxy-4,4′-biphenyldicarboxylic acid

Abstract

Three 3D lanthanide–organic frameworks (LOFs), [LnL(HCO₂)(DMF)]_n (Ln = Eu (1), Gd (2), Dy (3); H₂L = 2,2′-dimethoxy-4,4′-biphenyldicarboxylic acid), have been prepared by the solvothermal reaction of Ln(NO₃)₃·6H₂O and H₂L in DMF–H₂O mixed solvent. Crystallographic data show that LOFs 1–3 are isomorphous and crystallize in the orthorhombic space group Pna2₁. Each Ln(III) is eight-coordinated to four O atoms from four L²⁻ ligands, one O atom from the DMF molecule and three O atoms from HCO₂⁻. The adjacent Ln(III) ions are linked by the carboxylate groups of the L²⁻ ligands and HCO₂⁻ to form a 1D inorganic rod-shaped [Ln(CO₂)₂(HCO₂)]_n chain as a secondary building unit (SBU). The infinite 1D chains are interconnected by the biphenyl groups, giving rise to a 3D framework along the c axis. LOFs 1–3 are the first neutral Ln-carboxylate/HCO₂⁻ chain-based sra-nets. 1 exhibits characteristic luminescence of Eu³⁺ upon 343 nm excitation. The investigation of magnetic properties shows very weak ferromagnetic interactions (J = 0.0092(3) cm⁻¹) between Gd(III) ions in 2 with a Gd–O–Gd bridging angle of 125.6(1)°, and θ = −1.9(2) K in 3 due to thermal depopulation of the Stark levels of Dy(III) ions and/or the possible antiferromagnetic interactions between Dy(III) ions in contrast to the single-ion behavior observed in 1.