Construction of Stable Metal−Organic Frameworks by Integrating Phosphonic Groups into Building Blocks

Abstract

A novel metal-organic framework (MOF), constructed by Cu²⁺ and 4-phosphonobenzoic acid (H₃pbc), namely SL-1, was prepared via solvothermal synthesis in a mixture of H₂O and N,N-dimethylacetamide (DMA). The crystalline structure of SL-1 was revealed by single crystal X-ray diffraction (SC-XRD) analysis, which demonstrates the existence of two different coordination geometries of cooper nodes. Cu1 center is anchored by two carboxylate groups from two H₃pbc ligand and coordinates with three water molecules, while Cu2 center is six-coordinated that results in -CuO₆-CuO₆-CuO₆-CuO₆- double helix structure. Remarkably, the robust SL-1 demonstrates excellent acid and base resistance when soaking in aqueous solution with pH value ranging from 4–12. In addition, after a high temperature process (~100 °C), the water molecules linked by carboxylate anchored Cu node would be released, while the crystalline nature was preserved and almost unchanged. As a result, the exposed and unsaturated Lewis acid active sites can effectively catalyze aerobic oxidation of benzyl alcohol to benzaldehyde with yield of 73 % and selectivity of nearly 100 %. We believe the presented strategy by integrating phosphonic groups into building blocks to afford stable MOF structure will guide the design of more practical functionalized MOF materials.