From two-dimensional networks to three-dimensional metal–organic frameworks mediated by solvent ratio: luminescence and gas adsorption properties

Abstract

Under the same solvothermal conditions, two new coordination polymers, [Co(L)₂]_n (1) and {[Co₃(L)₄(NO₃)₂(H₂O)₄]·2H₂O}_n (2), and two novel isostructural metal–organic frameworks, {[Co(L)(NO₃)(H₂O)]·0.5H₂O}_n (3) and {[Ni(L)(NO₃)(H₂O)]·0.5H₂O}_n (4), were synthesized by using a new ligand, namely 4-(2-chloroimidazo[1,2-a]pyridin-3-yl)-[2,4′-bipyridine]-6-carboxylic acid (HL). 1–4 were fully characterized by infrared spectroscopy, elemental analyses, thermogravimetric analyses, powder X-ray diffraction, and single-crystal X-ray diffraction. Their dimensionality ranges from two-dimensional networks (1 with a (4,4) network and 2 with a quasi-“long and short brick” network) to three-dimensional frameworks (isostructural 3 and 4). The dimensional/structural diversities are mediated by the solvation level of nitrate anions which was adjusted only via changing the solvent ratio (acetonitrile : water). Interestingly, compared to 1 and 2, 3 and 4 display enhanced luminescence emission. The gas adsorption properties of 3 and 4 have also been investigated. The present work provides a promising approach to construct various coordination polymers or metal–organic frameworks by adjusting the solvent ratio, and to tune their properties.