Cobalt(II) and Cadmium(II) Metal–Organic Framework with Benzene-1,3,5-tricarboxylate and Viologen Guest: Stimuli-Responsive Photochromism, Volatile Amine Detection, and Hydrogen Generation

Two Co(II) and Cd(II) coordination polymers, {(Me₂bipy)[Co₅(btc)₃(Hbtc)(OH)]·2DMF·9H₂O} <i>_n</i> <b>(CoMOF)</b> and {(Me₂bipy)[Cd₂(μ₄-btc)₂]} <i>_n</i> (<b>OGU-2</b>), were synthesized and characterized using IR spectroscopy, elemental analysis, and powder and single-crystal X-ray diffraction techniques. The Cd1 ion is seven-coordinated, adopting a distorted monocapped trigonal prismatic geometry (CdO₇). <b>OGU-2</b> exhibits a 3D porous framework with a rare flu-3,6-<i>C</i>2/<i>c</i> topology. The framework contains one-dimensional channels along the <i>c</i> axis with dimensions of approximately 10 × 10 Ų. The photochromic behavior of <b>OGU-2</b> was investigated, revealing excellent chromic properties in response to multiple external stimuli, including UV light, temperature, and organic amines. <b>CoMOF</b>, a coordination polymer reported previously, along with <b>OGU-2</b>, was evaluated as a catalyst for hydrogen gas production via the methanolysis reaction of NaBH₄. The results demonstrated that these coordination polymers exhibited high catalytic activity for hydrogen production, comparable to the high values reported in the literature.