Hydrothermal syntheses, structural characterizations, and magnetic properties of five MOFs assembled from C2-symmetric ligand of 1,3-di(2′,4′-dicarboxylphenyl)benzene with various coordination modes

Abstract

Five new complexes, namely, [Ni(H₂DDB)(H₂O)₂(μ₂-H₂O)]_n (1), [Ni_1.5(DDB)(1,4-bib)_1.5(H₂O)]_n (2), {[Ni₂(DDB)(1,3-bib)₂(μ₂-H₂O)]·2H₂O}_n (3), [Cu₂(H₂DDB)₂(1,4-bib)₂]·H₂O (4), and {[Cu_1.5(HDDB)(1,2-bimb)]·H₂O}_n (5), have been synthesized using the solvothermal reaction of 1,3-di(2′,4′-dicarboxylphenyl)benzene (H₄DDB) with nickel(II) or copper(II) salts in the presence of ancillary ligands of bis(imidazole) linkers (1,4-bib = 1,4-bis(1H-imidazol-4-yl)benzene, 1,3-bib = 1,3-bis(1H-imidazol-4-yl)benzene, and 1,2-bimb = 1,2-bis(imidazol-1-ylmethyl)benzene). Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. In complex 1, Ni^II ions are bridged by associated water molecules to form an interesting [Ni(H₂DDB)(H₂O)₂(μ₂-H₂O)]_n chain structure, which is further extended to a 3D supramolecular structure via the hydrogen bonds. In complex 2, a novel 3D (3,3,6)-connected (6³)₄(6⁵·8⁸·10²) net is generated from the synergistic effect of 1D [Ni(1,4-bib)]_n zigzag chains and 2D [Ni₃(DDB)₂]_n bilayers. For complex 3, with the employment of 1,3-bib bis(imidazole) linker instead of 1,4-bib, an unprecedented binuclear {Ni₂(COO)(μ₂-H₂O)} SBUs based 3D (3,6)-connected (3·6·7)(3²·4³·5⁴·6³·7·8²) net was obtained. Furthermore, when Ni^II ions were replaced by Cu^II ions, a paddle wheel {Cu₂(COO)₄} SBUs based [Cu₂(H₂DDB)(1,4-bib)₂] (4) complex was formed. For complex 5, 2D [Cu₃(HDDB)₂]_n sheets are further linked by 1,2-bimb pillars to expand a paddle wheel {Cu₂(COO)₄} SBUs based 3D architecture with 4-connected (6⁵ 8)-cds topology. Moreover, the magnetic properties of 1, 3, and 5 have been investigated.