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.