Fluorescent Cadmium Bipillared‐Layer Open Frameworks: Synthesis, Structures, Sensing of Nitro Compounds, and Capture of Volatile Iodine

Fluorescent Cd metal–organic frameworks (MOFs), [Cd2(dicarboxylate)2(NI‐bpy‐44)2] (dicarboxylate=benzene‐1,4‐dicarboxylate (1,4‐bdc, 1), 2‐bromobenzene‐1,4‐dicarboxylate (Br‐1,4‐bdc, 2), 2‐nitrobenzene‐1,4‐dicarboxylate (NO2‐1,4‐bdc, 3), biphenyl‐4,4′‐dicarboxylate (bpdc, 4); NI‐bpy‐44=N‐(pyridin‐4‐yl)‐4‐(pyridin‐4‐yl)‐1,8‐naphthalimide)), featuring non‐ and twofold interpenetrating pcu‐type bipillared‐layer open structures with sufficient free voids of 58.4, 51.4, 51.5, and 41.4 %, respectively, have been hydro(solvo)thermally synthesized. MOFs 1–4 emitted solid‐state blue or cyan fluorescence emissions at 447±7 nm, which mainly arose from NI‐bpy‐44 and are dependent on the incorporated solvents. After immersing the crystalline samples in different solvents, that is, H2O and DMSO (1 and 2) as well as nitrobenzene and phenol (1–4), they exhibited a remarkable fluorescence quenching effect, whereas o‐xylene and p‐xylene (4) caused significant fluorescence enhancement. The sensing ability of MOFs 1–4 toward nitro compounds carried out in the vapor phase showed that nitrobenzene and 2‐nitrophenol displayed detectable fluorescence quenching with 1, 2, and 4 whereas 4‐nitrotoluene was an effective fluorescence quencher for 1 and 2; this is most likely attributed to their electron‐deficient properties and higher vapor pressures. Moreover, MOFs 1–4 are highly reusable for quick capture of volatile iodine, as supported by clear crystal color change and also by immense fluorescence quenching responses owing to the donor–acceptor interaction. Low‐pressure CO2 adsorption isotherms indicate that activated materials 1′–4′ are inefficient at taking up CO2. Cube root: The synthesis and crystal structures of four fluorescent Cd metal–organic frameworks (MOFs), [Cd2(dicarboxylate)2(NI‐bpy‐44)2] (dicarboxylate=benzene‐1,4‐dicarboxylate (1,4‐bdc, 1), 2‐bromobenzene‐1,4‐dicarboxylate (Br‐1,4‐bdc, 2), 2‐nitrobenzene‐1,4‐dicarboxylate (NO2‐1,4‐bdc, 3), biphenyl‐4,4′‐dicarboxylate (bpdc, 4); NI‐bpy‐44=N‐(pyridin‐4‐yl)‐4‐(pyridin‐4‐yl)‐1,8‐naphthalimide), featuring a pcu‐type bipillared‐layer open framework, and their potential for sensing small organic molecules and iodine capture are reported.