Microwave-Assisted Synthesis of Defects Metal-Imidazolate-Amide-Imidate Frameworks and Improved CO₂ Capture

In this work, we report three isostructural 3D frameworks, named <b>IFP-11</b> (R = Cl), <b>IFP-12</b> (R = Br), and <b>IFP-13</b> (R = Et) (IFP = Imidazolate Framework Potsdam) based on a cobalt­(II) center and the chelating linker 2-substituted imidazolate-4-amide-5-imidate. These chelating ligands were generated <i>in situ</i> by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under microwave (MW)-assisted conditions in DMF. Structure determination of these IFPs was investigated by IR spectroscopy and a combination of powder X-ray diffraction (PXRD) with structure modeling. The structural models were initially built up from the single-crystal X-ray structure determination of <b>IFP-5</b> (a cobalt center and 2-methylimidazolate-4-amide-5-imidate linker based framework) and were optimized by using density functional theory calculations. Substitution on position 2 of the linker (R = Cl, Br, and Et) in the isostructural <b>IFP-11</b>, <b>-12</b>, and <b>-13</b> allowed variation of the potential pore window in 1D hexagonal channels (3.8 to 1.7 Å). The potential of the materials to undergo specific interactions with CO₂ was measured by the isosteric heat of adsorption. Further, we resynthesized zinc based IFPs, namely <b>IFP-1</b> (R = Me), <b>IFP-2</b> (R = Cl), <b>IFP-3</b> (R = Br), and <b>IFP-4</b> (R = Et), and cobalt based <b>IFP-5</b> under MW-assisted conditions with higher yield. The transition from a nucleation phase to the pure crystalline material of <b>IFP-1</b> in MW-assisted synthesis depends on reaction time. <b>IFP-1</b>, <b>-3</b>, and <b>-5</b>, which are synthesized by MW-assisted conditions, showed an enhancement of N₂ and CO₂, compared to the analogous conventional electrical (CE) heating method based materials due to crystal defects