Rational Assembly of Co/Cd-MOFs Featuring Topological Variation

Three different carboxylate ligands of 4,4′-biphthalic acid (H4L, linear), 4,4′-axydiphthalic acid (H4LO, V-shaped), and thiophene-2,5-dicarboxylic acid (H2LS, V-shaped and heteroatomic ring) were selected as two-connected nodes to react with Co­(II) or Cd­(II) nitrates in the presence of 1,3,5-tris­(1-imidazolyl)­benzene (tib, Y-shaped and tridentate). Hydrothermal reactions in distilled water afforded seven new Co­(Cd)-MOFs, namely, M­(tib)­(H2L)­(H2O)2·H2O (M = Co, 1; Cd, 2), M2(tib)2(H2LO)2(H2O)2 (M = Co, 3; Cd, 4), Co2(tib)­(LO)·H2O (5), Co­(tib)­(LS)·2H2O (6), and Cd­(tib)­(LS)·3H2O (7). Of particular interest, they exhibit four interesting nets. 1–2 and 3–4 feature binodal (3,4) and (3,3,4,4)-connected nets if H-bonds are taken into account, respectively. 5 is composed of a two-dimensional metal-LO layer and a one-dimensional metal-tib chain and simplified into a 4-nodal (3,4,4,5)-connected net. 6 and 7 feature rare binodal (3,5)-connected {3.72}­{32.75.83} fsf/polar net and (3,5)-connected {63}­{69.8} hms net. Structural analyses show that each type of compound with the same metal components and tib ligands exhibit such interesting topological variations, which are derived from different orientations of three carboxylate ligands. Other properties of these compounds were also investigated, such as elemental and thermogravimetric analyses, photoluminescent spectroscopy, and magnetic behavior.