Flexible Co(II)-and Ni(II)-Based Cationic 2D Metal–Organic Frameworks Based on a Charge-Neutral (O,O)-Donor Bridge

Abstract

Two new metal–organic frameworks based on highly flexible 1,4-diazabicyclo[2.2.2]octane N,N′-dioxide (odabco) ligands were successfully synthesized and characterized. Their crystallographic formulae are [M(DMF)2(odabco)2](ClO4)2·dioxane, where M2+ = Co2+ (1) and Ni2+ (2), and DMF is N,N-dimethylformamide. The title compounds possess cationic 2D coordination networks filled with perchlorate anions and dioxane solvent molecules in the interlayer space, with 20% solvent accessible volume. Carbon dioxide adsorption measurements for desolvated samples 1a and 2a gave 511 m2/g and 377 m2/g specific surface areas, respectively, revealing the first example of gas adsorption properties in the structure based on a flexible odabco bridge, despite the presence of large counteranions within the positively charged network. Magnetization measurements for 1, 1a, 2 and 2a reveal their paramagnetic nature to be in a reasonable agreement with crystal structures, and almost no solvent dependence of the magnetization characteristics. A decrease in the effective magnetic moment observed at low temperatures is attributed mostly to zero-field level-splitting in the octahedral Ni2+ and Co2+ ions.

Keywords

• metal–organic framework
• coordination polymer
• cationic networks
• aliphatic ligands
• gas adsorption
• magnetic properties