Construction, Structural Diversity, and Properties of Seven Zn(II)-Coordination Polymers Based on 3,3′,5,5′-Azobenzenetetracarboxylic Acid and Flexible Substitute Bis(imidazole) Linkers

Flexible bis(imidazole) linkers incorporating methyl-, ethyl, and isopropyl-groups on imidazole rings were synthesized, and their seven Zn(II)-coordination polymers, namely, {[Zn-2(mu(4)-ao(2)btc)(mu-1,5-bipe)(2)]center dot 4DMF}(n) (1), {[Zn-2(mu(6)-ao(2)btc) (mu-1,5-bmeipe)]center dot 2DMA}(n) (2), {[Zn-2(mu(8)-ao(2)btc) (mu-1,5-beipe)]center dot DMA}(n) (3), {[Zn-4(mu(8)-ao(2)btc) (mu-1,5-bisoipe)(2)]center dot 2DMF}(n) (4), {[Zn-2(mu(4)-ao(2)btc)(mu-1,6-bih)(1.5) (DMA)]center dot 2DMA}(n) (5), {[Zn-2(mu(8)-abtc)(mu-1,6-bmeih)]center dot DMF}(n) (6), and {[Zn-2(mu(8)-ao(2)btc) (mu,1,6-beih)]center dot DMF}(n) (7) (ao(2)btc = dioxygenated form of 3,3',5,51-azobenzenetetracarboxylate, 1,5-bipe: 1,5-bis(imidazol-1yl)pentane, 1,5-b(x)ipe: 1,S-bis(2-x-imidazol-1-yl)pentane = methyl-, ethyl-, isopropyl-), 1,6-bih: 1,6-bis(imidazol-1-yOhexane, 1,6-b(x)ih = 1,6-bis(2-y-imidazol-1-yl)hexane (y = methyl-, ethyl-)), were obtained with azobenzenetetracarboxylic acid to investigate the effect of substitute groups of bis(imidazole) ligands on structural diversity and characterized by elemental analyses, IR spectra, single -crystal X-ray diffraction, powder X-ray diffraction, and thermal analyses (TG/DTA). X-ray results demonstrated that complex 1 had a two-dimensional (2D) structure, while the other complexes were three-dimensional (3D) coordination polymers. For complexes 1-4, the dimensionality increased with the steric hindrance on imidazole rings. Complexes 2-7 were 3D frameworks with one-dimensional (1D) channels, and their 1D channel sizes decreased with the change of substitute groups from -CH3 to -CH(CH3)(2). For complexes 3, 4, 6, and 7, paddlewheel Zn-2(CO2)(4) binuclear secondary building units occurred with the increase of steric hindrance of substitute groups on imidazole rings. CO2 adsorption results of the complexes showed that uptake capacities decreased with the increase of length of substitute alkyl groups from methyl- to isopropyl- in channels. Furthermore, photoluminescence and topological properties of the complexes were studied.