Hydrothermal synthesis and structural characterization of metal–organic frameworks based on new tetradentate ligands

Abstract

The hydrothermal reaction of two new tetradentate ligands with different metal salts of cadmium nitrate, zinc chloride, cobalt nitrate and deprotonated terephthalic acid (H₂tp), isophthalic acid (H₂ip), 4,4′-oxybisbenzoic acid (H₂obba) in H₂O/DMF or H₂O/methanol gave three metal–organic frameworks (MOFs): {[Zn₂(L1)(tp)(formate)₂]·H₂O}_n (1), {[Cd₂(L2)(ip)₂]·2H₂O}_n (2), {[Co₂(L2)(obba)₂]}_n (3) (L1 = 1,2-bis {2,6-bis [(1H-imidazol-1-yl) methyl]-4-methylphenoxy} ethane, L2 = 1,3-bis {2,6-bis [(1H-imidazol-1-yl) methyl]-4-methylphenoxy} propane). The structures of the frameworks are established by single-crystal X-ray diffraction. Compound 1 is a three-dimensional (3D) framework with a 2-fold interpenetrated form, which exhibits a 2-nodal (3,4)-connected fsh-3,4-P2₁/c net with a {8³}₂{8⁵·10} topology. Compound 2 has a 2-nodal (4,8)-connected 3D framework where the dinuclear cadmium cluster secondary building units (SBUs) assemble with isophthalate and ligand L2 to construct a rare topological type sqc22 net with a {3²·5⁴}{3⁴·4⁴·5¹⁰·6¹⁰} topology. Whereas, Compound 3 can be extended to a 2D interlocked (4,4)-connected 4,4 L28 net with the point symbol {4·6⁴·8}₂{4²·6⁴}. L1 and L2 are tetradentate ligands with diverse linkers and display different coordination modes. In addition, the thermal stability and photochemical properties of the frameworks are also investigated.