Crystalline to Crystalline Phase Transformations in Six Two-Dimensional Dynamic Metal–Organic Frameworks: Syntheses, Characterizations, and Sorption Studies

Six dynamic metal–organic frameworks, namely, {[Cd(1,4-bib)(glut)]·(4H2O)}n (1), {[Zn(1,4-bib)(glut)]·(4H2O)}n (2), {[Co(1,4-bib)(3,5-pydc)]·(2H2O)}n (3), {[Mn(1,4-bib)(3,5-pydc)]·(2H2O)}n (4), {[Zn(1,4-bib)(3-mglut)]·(4H2O)}n (5), and {[Zn(1,4-bib)(2,2′-dmglut)]·(2H2O)}n (6) from 1-(4-(1H-imidazole-1-yl)butyl)-1H-imidazole (1,4-bib) using four different dicarboxylic acids salt [disodium glutarate (Na2glut), pyridine-3,5-dicarboxylate (3,5-pydc), 3-methyl glutarate (3-mglut), 2,2′-dimethyl glutarate (Na22,2′-dmglut)], and four different divalent transition metal ions have been synthesized. Out of these, the structure of compound 3 has been previously reported although synthesized in different method, whereas the rest of the compounds are new. All of these synthesized compounds are characterized by single crystal and powder X-ray diffraction and other physicochemical methods. All the compounds exhibit 2D structure as evident by single crystal X-ray studies. Interestingly, all of these compounds show crystalline to crystalline phase transformation. Variable temperature PXRD study indicates compounds 1 and 6 show single-step phase transformation and the rest show two-step phase transformation upon desolvation. All of these transformations have also been established by IR spectroscopy. Among the structural transformations listed, 1–5 show reversible crystalline to crystalline phase transformation on desolvation and resolvation, whereas 6 shows an irreversible transformation. All of these transformations are thoroughly investigated by PXRD and IR spectroscopy. Sorption studies with CO2 and N2 were also performed for all the metal–organic frameworks and characteristic surface adsorptions are found in all the cases.