Rare 3D Heterometallic-Organic Frameworks Built from [M₆] (M = Zr, Hf) and [Cu₂I₂] Clusters for Iodine Vapor Capture

Precisely synthesizing Zr/Hf-oxo and 3d metal cluster-based heterometallic-organic frameworks (HMOFs) still faces huge challenges: coordination competition between Zr⁴⁺/Hf⁴⁺ and 3d metal ions toward ligands and crystallization difficulties inherent to Zr/Hf-oxo cluster systems. Herein, we chose an eight-connected [M₆(μ₃-O)₄(μ₃-OH)₄(OH)₄(H₂O)₄]⁸⁺ (M = Zr, Hf) motif and a four-connected [Cu₂I₂] cluster as second building units and linear isonicotinate (INA) as an organic linker to construct two rare three-dimensional HMOFs {[Zr₆(μ₃-O)₄(μ₃-OH)₄(OH)₄(H₂O)₄][(Cu₂I₂)(INA)₄]₂·8H₂O·7DMF}_n (NS-7) and {[Hf₆(μ₃-O)₄(μ₃-OH)₄(OH)₄(H₂O)₄][(Cu₂I₂)(INA)₄]₂·8H₂O·7DMF}_n (NS-8) via self-assembly under solvothermal condition. Activated NS-7 and NS-8 with amorphous nonmicroporous structures still exhibited high iodine adsorption capacities of 2.09 and 1.87 g·g^-1 via the confirmation of static iodine vapor adsorption experiments, respectively, being superior to most previously reported pure Zr-/Hf-oxo or copper(I)-iodide cluster-based metal-organic frameworks. Our work not only enriches the documents of Zr-/Hf-oxo cluster-based HMOFs but also provides some instructive suggestions in the design and synthesis of novel multicomponent cluster-based metal-organic frameworks.