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.