Unique two-fold interpenetration of 3D microporous 3d–4f heterometal–organic frameworks (HMOF) based on a rigid ligand

Abstract

Six heterometal–organic frameworks, {[LnCu_1.5(BPDC)₃(H₂O)₂]·mH₂O}_n (Ln = Gd (1, m = 4.75), Tb (2, m = 3.75), Eu (3, m = 5), Ho (4, m = 2), Yb (5, m = 2.25), BPDC = 4,4′-dicarboxylate-2,2′-dipyridine anion), and {[LuCu_1.5(BPDC)₃(H₂O)_1.5]·2.5H₂O}_n (6), have been synthesized under hydrothermal conditions. The structure analyses for 1–6 reveal that the six compounds are isomorphous, belonging to the monoclinic system with space groupC2/c, and display two-fold interpenetrating 3D frameworks, which are the first examples of d–f heterometal–organic frameworks based on a rigid ligand. These frameworks were further characterized by elemental analyses, TG analysis, PXRD, hydrogen adsorption and variable-temperature magnetic susceptibilities. Interestingly, hydrogen adsorption was significantly observed under the existence of the two-fold interpenetration. Magnetic investigations suggest that the ferromagnetic coupling exists between Gd³⁺ and Cu²⁺ in 1, and that the nature of the interaction between Ln³⁺ and Cu²⁺ ions in compounds 2, and 4–6 cannot be absolutely determined when χ_MT values are reduced with decreasing temperature.