Ionothermal Syntheses, Crystal Structures and Luminescence of Two Lanthanide-Carboxylate Frameworks based on the 1,4-Naphthalenedicarboxylate and Oxalate Mixed Ligands

Ionothermal reactions of Ln(NO3)(3) [Ln = Eu (1), Sm (2)] with 1,4-naphthalenedicarboxylic acid (1,4-H(2)ndc) and oxalic acid (H(2)ox) in 1-ethyl-3-methylimidazolium bromide (EMIM-Br) ionic liquid (IL) afforded two lanthanide compounds, namely, {(EMIM)[Ln(1,4-ndc)(ox)(0.5)Br]}(n) [Ln = Eu (1), Sm (2)]. The two isomorphous compounds consist of anionic three-dimensional lanthanide-carboxylate frameworks and extraframework charge-balancing species of [EMIM](+) cations. Both compounds are 6-connected pcu topological nets based on the dinuclear lanthanide secondary building units. It is noted that the cationic and anionic components of the IL are incorporated into the structures under the present ionothermal conditions. Moreover, the use of IL solvent for preparation of the lanthanide compounds can prevent the coordination of water and organic solvent molecules from central lanthanide atoms effectively. Detailed photoluminescence studies showed both compounds exhibit typical lanthanide luminescent emissions. An efficient excitation energy transfer from organic ligand-to-Eu-III ion is observed in compound 1.