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

Under the same solvothermal conditions, two new coordination polymers, [Co(L) 2 ] n ( 1 ) and {[Co 3 (L) 4 (NO 3 ) 2 (H 2 O) 4 ]·2H 2 O} n ( 2 ), and two novel isostructural metal-organic frameworks, {[Co(L)(NO 3 )(H 2 O)]·0.5H 2 O} n ( 3 ) and {[Ni(L)(NO 3 )(H 2 O)]·0.5H 2 O} 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. Various two-dimensional networks ((4,4) network and unique quasi-"long and short brick" network) and three-dimensional frameworks are induced only through changing the solvent ratio (acetonitrile : water).