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

Abstract

Flexible bis(imidazole) linkers incorporating methyl-, ethyl, and isopropyl- groups on imidazole rings were synthesized, and their seven Zn(II)-coordination polymers, namely, {[Zn<inf>2</inf>(μ<inf>4</inf>-ao<inf>2</inf>btc)(μ-1,5-bipe)<inf>2</inf>]·4DMF}<inf>n</inf> (1), {[Zn<inf>2</inf>(μ<inf>6</inf>-ao<inf>2</inf>btc)(μ-1,5-bmeipe)]·2DMA}<inf>n</inf> (2), {[Zn<inf>2</inf>(μ<inf>8</inf>-ao<inf>2</inf>btc)(μ-1,5-beipe)]·DMA}<inf>n</inf> (3), {[Zn<inf>4</inf>(μ<inf>8</inf>-ao<inf>2</inf>btc)(μ-1,5-bisoipe)<inf>2</inf>]·2DMF}<inf>n</inf> (4), {[Zn<inf>2</inf>(μ<inf>4</inf>-ao<inf>2</inf>btc)(μ-1,6-bih)<inf>1.5</inf>(DMA)]·2DMA}<inf>n</inf> (5), {[Zn<inf>2</inf>(μ<inf>8</inf>-abtc)(μ-1,6-bmeih)]·DMF}<inf>n</inf> (6), and {[Zn<inf>2</inf>(μ<inf>8</inf>-ao<inf>2</inf>btc)(μ-1,6-beih)]·DMF}<inf>n</inf> (7) (ao<inf>2</inf>btc = dioxygenated form of 3,3′,5,5′-azobenzenetetracarboxylate, 1,5-bipe: 1,5-bis(imidazol-1-yl)pentane, 1,5-b(x)ipe: 1,5-bis(2-x-imidazol-1-yl)pentane (x = methyl-, ethyl-, isopropyl-), 1,6-bih: 1,6-bis(imidazol-1-yl)hexane, 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 -CH<inf>3</inf> to -CH(CH<inf>3</inf>)<inf>2</inf>. For complexes 3, 4, 6, and 7, paddlewheel Zn<inf>2</inf>(CO<inf>2</inf>)<inf>4</inf> binuclear secondary building units occurred with the increase of steric hindrance of substitute groups on imidazole rings. CO<inf>2</inf> 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. © 2016 American Chemical Society.