UoC-7: A Bimetallic K-Zn-MOF with an Anionic Framework Based on Fluorinated Trimesate Ligands Exhibiting a Large CO 2 Uptake.

In solvothermal reactions of Zn(NO 3 ) 2 ×6H 2 O with K(H 2 mF-BTC) or K(H 2 dF-BTC) in DMF/ethanol or DMA/ethanol solvent mixtures, single crystals of the MOFs UoC-7(1F) and UoC-7(2F) were obtained crystallizing in the hexagonal space group P6 3 /m (no. 176) (H 3 BTC: 1,3,5-benzenetricarboxylic acid; mF-/dF: mono-/difluoro; DMF: N,N-dimethylformamide; DMA: N,N-dimethylacetamide; UoC: University of Cologne). According to the general composition [(CH 3 ) 2 NH 2 ][K 2 Zn 3 (mF-/dF-BTC) 3 (H 2 O)]×solvent, UoC-7 consists of an anionic bimetallic framework. The charge is compensated by a (CH 3 ) 2 NH 2 + cation stemming from the (partial) hydrolysis of the solvent. The crystal structure shows large channels along the hexagonal [001] direction, which accommodate the cations as well as solvent molecules. Surface areas (S BET ) of 2740 m 2 /g (UoC-7(1F)) and 1643 m 2 /g (UoC-7(2F)) were obtained from N 2 sorption measurements. UoC-7 shows structural similarities to the MOF NKU-521 with a 5-(1H-tetrazol-5-yl)isophthalate linker. Both MOFs exhibit a 4,7,8T14 topology. Despite smaller channels in UoC-7 compared to NKU-521, the CO 2 uptake is considerably higher (~164 cm 3 /g at 1 bar/293 K) being one of the highest CO 2 uptakes observed up to now.