Synthesis, structures and luminescence properties of 3d–4f heterometallic–organic frameworks (HMOFs) constructed from different copper halide clusters

Four novel 3d–4f heterometallic–organic frameworks (HMOFs), namely [Gd₂(Cu₂I₂)(C₆H₄NO₂)₆(C₃H₇NO)(H₂O)]·(C₃H₇NO) (1), [Gd₂(Cu₄I₄)(C₆H₄NO₂)₆(C₃H₇NO)₂] (2), [Gd₂(Cu₆I₆)(C₁₂H₈NO₂)₆(C₂H₆O)₂(H₂O)₂] (3) and [Gd₂(Cu₈I₈)(C₁₂H₈NO₂)₆(H₂O)₄]·5(C₄H₈O₂) (4), have been solvothermally synthesized and characterized. The four compounds incorporate Cu₂I₂, Cu₄I₄, Cu₆I₆ and Cu₈I₈ clusters in three-dimensional frameworks, respectively, and the influence of Ln³⁺ ions, copper halide clusters and ligands on the construction of the structures has been analyzed. The four compounds display four different emission colours. Interestingly, compound 3 responds to external mechanical force. After grinding, the fluorescence has been obviously quenched. Compound 4 displays a reversible luminescence behavior, accompanying the removal and recovery of the guest molecules in the channel.