Two New MOFs Based on Cu₂ Paddlewheel Units and Biphenyltetracarboxylate Ligands with a Different Degree of Fluorination

Abstract

Two new MOFs (metal‐organic frameworks), namely 3∞[Cu2(H2O)2(L)]·3DMF·H2O [L = 4‐fluoro‐biphenyl‐3,3′,5,5′‐tetracarboxylate (4‐mF‐BPTC4–) and 4,4′‐difluoro‐biphenyl‐3,3′,5,5′‐tetracarboxylate (4,4′‐dF‐BPTC4–)] termed UoC‐1(1F) and UoC‐1(2F) (UoC ≡ University of Cologne), were synthesized by solvothermal reactions in DMF. The crystal structure of UoC‐1(1F) was solved and refined from X‐ray single crystal data (Imma, Z = 4). The X‐ray powder diffraction data of UoC‐1(2F) confirmed that both MOFs are isostructural. In their crystal structures each of the four carboxylate groups of the BPTC4– linker is involved in a Cu2 paddlewheel unit leading to a 3D structure with high porosity, which was confirmed by N2 gas sorption measurements revealing specific surface areas of SBET = 1256 m2·g–1 [UoC‐1(1F)] and 1162 m2·g–1 [UoC‐1(2F)] after activation at 120 °C for 72 h. Higher activation temperatures lead to a decomposition of the framework and significantly decreased specific surface areas.

Two New Coordination Polymers with UO22+ Units and Fluorinated Aromatic Carboxylate Linkers

“…Nevertheless, a higher torsion angle is observed with F3 in α position, which is different to most reports in the literature , . In our former work with the monofluorinated 4‐ mF ‐BPTC 4– linker we found a torsion angle of 28.9(9)°, which is significantly larger than those found for anion A in this work.…”

“…One of these DMA molecules is disordered over two positions and the fluoro substituent of the linker anion is disordered over two positions as well. A similar disorder of the fluoro group was found in our preceding work with this ligand . In Figure , the coordination spheres around U1 and U2 are given, details of the crystal structure analysis are presented in Table .…”

“…Anion B is coordinating with its four carboxylate groups in a chelating bidentate mode to two U1O 2 2+ and two U2O 2 2+ units. The torsion angles are 9.9(16)° and 10.4(14)°, respectively, again significantly smaller than those found in UoC‐1(1F) . For symmetry reasons, the F1 substituent of anion B always shows a 50 % occupancy.…”

“…Several years ago we started to synthesize fluorinated aromatic carboxylic acids,, which – in a next step – were used to synthesize new CPs and MOFs with these linkers . With respect to their structural chemistry it is a remarkable feature that the torsion angle between the phenyl ring and the carboxylate group is no longer close to 0° as found in most MOFs and CPs with non‐fluorinated ligands, but significantly increased especially for fluoro substituents in α position and even more for perfluorinated ligands , .…”

“…In this respect, it seems to be worthwhile to examine how the structural chemistry of uranium‐based CPs and MOFs develops, when fluorinated aromatic carboxylate ligands are introduced. In the following we will present two such examples based on mono‐ and difluorinated biphenyl‐3,3',5,5'‐tetracarboxylates, which were introduced recently by us as suitable linkers for the construction of highly porous MOFs . Here, two coordination polymers are formed with a layer‐like polymeric structural subunit.…”