Porous Manganese(II) 3-(2-Pyridyl)-5-(4-Pyridyl)-1,2,4-Triazolate Frameworks: Rational Self-Assembly, Supramolecular Isomerism, Solid-State Transformation, and Sorption Properties

Reactions of 3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (Hdpt24) with Mn(OAC)(2) under different conditions give two mononuclear complexes, [Mn(dpt24)(2)(MeOH)(2)] (1) and [Mn(dpt24)(2)(H2O)(2)] center dot 6H(2)O (2), and three isomeric two-dimensional (2D) coordination polymers alpha-[Mn(dpt(2)](3a), beta-[Mn(dpt24)(2)] . g (3b . g, g = DMF and H2O), and gamma-[Mn-(dpt24)(2)] . g (3c . g, g = toluene and MeOH). Their structures were characterized by single-crystal and powder X-ray diffractions. In these compounds, four coordination sites of each octahedrally coordinated Mn-II ion are chelated by two dpt24 ligands in the transand/or cis configurations. While the two remaining coordination sites are occupied by solvent molecules in 1 and 2, they are occupiea by pyridyl nitrogens from neighboring Mn(dpt24)(2) units in 3, forming 4-connected 2D (4,4) networks. The Mn-II ions in both 3a and 3b are uniquely chelated by dpt24 in the trans or cis configurations, respectively, but Mn(dpt24)(2) in 3c possesses both the trans and cis configurations. The packing fashions of these (4,4) layers in the three isomers of 3 are also different, in which 3a has a close packing structure, while 3b exhibits unique one-dimensional (1D) channels and 3c exhibits two distinct types of 1D channels. As revealed by powder X-ray diffractions, crystals of 1 and 2 can reversibly transform to each other when in contact with the corresponding solvent vapor (H2O/MeOH). The gas and vapor sorption studies for porous 3b revealed interesting sorption behaviors. Nitrogen adsorption for 3b was observed at 195 K rather than 77 K, demonstrating the temperature-controlled framework flexibility. It also exhibited high selectivity and storage capacity for carbon dioxide over methane and nitrogen at room temperature. Moreover, 3b also demonstrated potential to separate organic chemicals with similar boiling points, such as benzene and cyclohexane, via pressure swing adsorption process.