Adjusting the Porosity and Interpenetration of Cadmium(II) Coordination Polymers by Ligand Modification: Syntheses, Structures, and Adsorption Properties

A series of structurally related rigid imidazole ligands, 1,4-bis(imidazol-1-yl)benzene (L-1), 1,4-bis(benzoimidazol-1-yl)benzene (L-2), and 4,4'-bis(benzoimidazol-1-yl)biphenyl (L-3), have been utilized to construct coordination polymers. The reactions of CdX2 (X = BF4- or ClO4-) with these ligands afford three new three-dimensional networks, {[Cd(L-1)(3)](BF4)(2)(CHCl3)(2)}(infinity) (1), {[Cd(L-2)(3)]ClO4)(2)(CHCl3)(4)(CH3OH)(2)}(infinity) (2), and {[Cd(L-3)(3)](ClO4)(2)}(infinity) (3). Compounds 1-3 are all alpha-Po metal-organic frameworks (MOFs) based on six-connected Cd-II nodes which are octahedrally coordinated by six nitrogen atoms of ligand molecules. Complex 2 represents a distorted alpha-Po framework with noninterpenetration, whereas 1 and 3 both exhibit a double interpenetrating alpha-Po network. These results suggest that the degree of interpenetration is tunable by ligand modifications, that is, varying the ligand spacer or terminal group. The three complexes exhibit a different void volume in their network. Gas adsorption measurements indicate that 3 possesses moderate gas-adsorption ability for CO2, and the progress of adsorption and desorption is reversible.