A new series of trivalent lanthanide (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) coordination polymers with a 1,2-cyclohexanedicarboxylate ligand: synthesis, crystal structure, luminescence and catalytic properties

Abstract

Eight lanthanide coordination polymers (Ln(1,2-chdc)(form)(H₂O)) have been solvothermally synthesized from the reaction of 1,2-cyclohexane dicarboxylic acid (denoted as 1,2-chdcH₂) with trivalent metallic cations (Ce³⁺ (1), Pr³⁺ (2), Nd³⁺ (3), Sm³⁺ (4), Eu³⁺ (5), Gd³⁺ (6), Tb³⁺ (7) and Dy³⁺ (8); from a nitrate or chloride source) in a mixed H₂O/N,N-dimethylformamide solvent (DMF) at T = 100–150 °C (form = formate ligand). Their crystal structures are similar and built up from nine-fold coordinated lanthanide cations (LnO₉ – tricapped trigonal prism), linked to each other through three Ln–O–Ln bonds (face sharing connection mode of LnO₉ polyhedra) in order to generate infinite ribbons. The coordination sphere of the lanthanide center is ensured by oxygen atoms from the 1,2-chdcH₂ ligand and formate groups. The latter come from the partial solvothermal decomposition of DMF solvent. The resulting compounds exhibit a layered structure with infinite chains of LnO₉, connected to each other via the ditopic 1,2-chdc linker. Luminescence studies (steady-state excitation, emission and time-resolved decay measurements) have been performed on the compounds bearing Ce³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Tb³⁺, and Dy³⁺ cations. The Nd compound (3) was found to be efficient for isoprene (methyl-2-butadiene, CH₂CH–C(Me)CH₂) polymerization despite the presence of water in its molecular structure, affording a highly cis stereo-regular polymer.