Metal–organic frameworks based on transition-metal carboxylate clusters as secondary building units: synthesis, structures and properties

Abstract

Five new metal–organic frameworks, [Zn_2.5(SIP)(azopy)_1.5(OH)₂(H₂O)]_n (1), {[Zn_1.5(SIP)(azopy)_1.5(H₂O)₂]·0.5(azopy)·2H₂O}_n (2), {[Cd_1.5(SIP)(azopy)_1.5(H₂O)₂]·0.5(azopy)·2H₂O}_n (3), {[Cd_2.25(SIP)_0.5(μ₃-OH)₃(H₂O)]·0.5H₂O}_n (4), and [Cu₃(SIP)(CH₃COO)(μ₃-OH)₂(μ₂-H₂O)(H₂O)]_n (5) were produced by hydrothermal reactions of NaH₂SIP (NaH₂SIP = 5-sulfoisophthalic acid monosodium salt) with azopy (azopy = 4,4′-azobispyridine). They were structurally characterized by single-crystal X-ray diffraction and elemental analysis. In the formation of these compounds, transition-metal carboxylate clusters as secondary building units (SBUs) play important roles. 1 crystallizes in the triclinic P space group and exhibits a 3D metal–organic framework with typical pcu topology. 2 and 3 are isomorphic and crystallize in the monoclinic space groupP2/c, both feature an interesting 3D coordination framework with an unprecedented {6².8⁴}{6³}²{6⁴.8²}² topological structure, which has been deposited in the Reticular Chemistry Structure Resource (RSCR) named as zlm net. 4 crystallizes in the monoclinic C2/m space group and displays a 3D architecture with interesting coordination modes. 5 crystallizes in the triclinic space group P and possesses a 2D coordination configuration with a hexanuclear Cu₆O₄(COO)₆ cluster as the secondary building unit. The luminescence analysis on 1–3 and the magnetic analysis on 5 were performed and discussed.