Effect of Solvent Molecule in Pore for Flexible Porous Coordination Polymer upon Gas Adsorption and Iodine Encapsulation

Four new Zn­(II)-coordination polymers,
namely, [Zn2(μ6-ao2btc)­(μ-obix)2]n (1), [Zn2(μ4-ao2btc)­(μ-obix)2]n (2), [Zn2(μ4-ao2btc)­(μ-mbix)2]n (3), and {[Zn2(μ4-ao2btc)­(μ-pbix)2]·2DMF·8H2O}n (4), where ao2btc = dioxygenated form of 3,3′,5,5′-azobenzenetetracarboxylate
and obix, mbix, and pbix = 1,2-, 1,3-, and 1,4-bis­(imidazol-1-ylmethyl)­benzene,
have been synthesized with azobenzenetetracarboxylic acid and isomeric
bis­(imidazole) ligands and characterized by elemental analyses, IR
spectra, single-crystal X-ray diffraction, powder X-ray diffraction,
and thermal analyses. X-ray results showed that 1, 2, and 4 had two-dimensional structures with
3,4L13 topology, while 3 was a three-dimensional coordination
polymer with bbf topology. For 4, two types of activation
strategies, solvent exchange + heating (which produced 4a) and direct heating (which produced 4b), were used
to investigate the effect of a guest molecule in a flexible framework.
Gas adsorption and iodine encapsulation properties of activated complexes
were studied. The CO2 uptake capacities for 4a and 4b were 3.62% and 9.50%, respectively, and Langmuir
surface areas calculated from CO2 isotherms were 167.4
and 350.7 m2/g, respectively. Moreover, 4b exhibited 19.65% and 15.27% iodine uptake in vapor phase and cyclohexane
solution, respectively, which corresponded to 1.47 and 0.97 molecules
of iodine/formula unit, respectively. Moreover, photoluminescence
properties of the complexes were studied.