Structural diversity of four lanthanide metal–organic frameworks based on 2,6-naphthalenedicarboxylate: synthesis, structures and photoluminescent properties

Abstract

We report the crystal structures of four different neutral lanthanide (Ln = La, Nd, Eu and Gd) metal–organic frameworks based on the organic linker 2,6-naphthalenedicarboxylate (NDC). The materials are three-dimensional and crystallize in three distinct topologies, with distinct bonding modes of NDC and lanthanide coordination numbers ranging from seven to nine and varying geometry. We denote our materials SLUG-49 [La₆(NDC)₉(DMF)₃·6 DMF], -50 [Nd₂(NDC)₃O(DMF)₂], -51 [Eu₂(NDC)₃(DMF)₂·DMF], and -52 [Gd₄(NDC)₆(DMF)₄] (DMF = N,N-dimethylformamide). The structures exhibit similar thermal decomposition profiles and infrared spectra. The Eu(III)-based material exhibits a sharp red-orange luminescence at 613 nm with a quantum efficiency of 3.56%.