The structure and properties of a 3D pillared-layered metal organic framework Cu(II)-diphosphonate

By introducing the second bridging ligand, 4,4′-bipyridyl (4,4′-bipy), the first 3D example of a Cu(II)-diphosphonate-4,4′-bipy metal organic framework (MOF), [Cu3(L)(4,4-bipy)(OH)2] 1 (H4L = H2O3P(C6H4)2PO3H2) was hydrothermally obtained and characterized through powder X-ray diffraction, elemental analysis, IR, and TG-DSC. Single-crystal X-ray diffraction revealed that compound 1 has a 3D MOF structure which is created by a 2D inorganic layer [Cu3O6P2]n through 4,4′-bipy and an organic biphenyl moiety of H4L linkages. In the structure, an inorganic layer and two organic pillars were alternately arranged. The results of fluorescence measurements revealed two decayed emission bands centered at 442 and 374 nm (λex = 236 nm) may be caused by the intraligand π∗–π emission states of the 4,4′-bipy ligand (λem = 442 and 381.5 nm, λex = 236 nm). Magnetism analysis indicated antiferromagnetic interactions between the metal centers within the 1D magnetic chain {–Cu(1)–Cu(2)–Cu(2)–Cu(1)–}n.

Graphical abstractA new 3D double-pillar-layer diphosphonate MOF [Cu3(L)(4,4′-bipy)(OH)2] 1 is obtained under hydrothermal conditions. Fluorescent analysis of 1 shows two fluorescent emission bands centered at 442 and 374 nm (λex = 236 nm) may be derived from the intraligand π∗–π emission states of the 4,4′-bipy ligand. Magnetism data indicate antiferromagnetic property between metal centers within 1D magnetic chain built by {–Cu(1)–Cu(2)–Cu(2)–Cu(1)–}n.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The 3D Cu(II)-diphosphonate-4,4′-bipy MOF is obtained under hydrothermal conditions. ► Fluorescent bands of 1 are caused by the intraligand π∗–π transition of the 4,4′-bipy. ► Magnetic analysis indicates an antiferromagnetic property between metal centers in 1.