Tunable gas adsorption properties of porous coordination polymers by modification of macrocyclic metallic tectons

Abstract

By using the semi-rigid ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid (H₄TCM) and various macrocyclic metallic tectons, eight new Ni(II) coordination polymers, namely, [(NiL¹)₂(TCM)]·17H₂O (1), [(NiL²)₂(TCM)]·17H₂O (2), [(NiL³)₂(TCM)]·18H₂O (3), [(NiL⁴)₂(TCM)]·4DMF·10H₂O (4), [(NiL⁵)₂(TCM)]·4DMF·9H₂O (5), [(NiL⁶)₂(TCM)]·20H₂O (6), [(NiL⁷)₂(TCM)]·18H₂O (7), [(NiL⁸)₂(TCM)]·4H₂O (8) (L¹ = 1,8-dimethyl-1,3,6,8,10,13-hexaaza-cyclotetradecane, L² = 1,3,6,9,11,14-hexaaza-tricyclooctadecane, L³ = 1,3,6,10,12,15-hexaaza-tricycloeicosane, L⁴ = 1,3,6,8,11,14-hexaaza-tricyclooctadecane, L⁵ = 4-methyl-1,3,6,8,11,14-hexaaza-tricyclooctadecane, L⁶ = 1,3,6,8,12,15-hexaaza-tricycloeicosane, L⁷ = 11-methyl-1,4,8,10,13,15-hexaaza-tricycloicosane and L⁸ = 3,10-diisobutyl-1,3,5,8,10,12-hexaaza-cyclotetradecane), were synthesized and structurally characterized. Single crystal X-ray analyses reveal that compounds 1–8 exhibit a similar diamondoid (dia) topology network. Regulated by macrocyclic metallic tectons, compounds 1–3 feature a three-dimensional (3D) framework with 7-fold interpenetration, giving rise to a 1D porous channel with size of ca. 1 nm. Compounds 4–7 possess a 3D network with 2D porous channels (porous size ca. 0.5 nm) and 4-fold interpenetration. Compound 8 shows a 3D dense packing arrangement with 2-fold interpenetration. The porosity of compounds 1–7 was confirmed by N₂ gas adsorption measurements at 77 K. Furthermore, due to functional groups exposed on the porous surface, activated compound 3 exhibits selective adsorption of CO₂ over N₂. The results show the crystal structure, stability and gas adsorption can be tuned by the modification of macrocyclic metallic tectons.