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

Six heterometal-organic frameworks, {[LnCu1.5(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 {[LuCu1.5(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 group C2/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 MT values are reduced with decreasing temperature.