Cu(II) MOFs Based on Bipyridyls: Topology, Magnetism, and Exploring Sensing Ability toward Multiple Nitroaromatic...

In this work, a series of three copper(II) metal-organic frameworks (MOFs), [Cu(4,4'-DP)Cl] (1), [Cu(4,4'-DP)_0.5Cl] (2), and [Cu(4,4'-TMDP)Cl] (3) (4,4'-DP = 4,4'-dipyridyl, 4,4'-TMDP = 4,4'-trimethylenedipyridyl), is designed and synthesized under solvothermal conditions. Crystallographic investigations reveal that 1 and 2 have tetrahedral and 3 has octahedral environment around the Cu(II) ion. By varying the solvent conditions and ligand derivatives, the topology can be interestingly tuned. TOPOS Pro provides topological conclusions that 1 is stabilized by unusual 2D + 2D → 3D polycatenation of layers lying in (110) and (11̅0) planes with dihedral angle of 90° showing altogether , , and topologies. On the other hand, 2 exhibits a (3,4-c net) topology and 3 shows 4-fold interpenetration with the topology. The dc measurements for 1-3 performed on polycrystalline samples in a 0.1 T field confirm strong ferromagnetic behaviors for 1 and 2 and moderate antiferromagnetic behavior for 3. To examine the sensing properties of the three MOFs, various hazardous nitroaromatic compounds (NACs) were used as analytes. While 1 is a potent fluorescence sensor for highly sensitive detection of multiple NACs, 2 selectively detects meta-dinitrobenzene (m-DNB) with K _SV = 5.73 × 10⁵ M^-1 and a remarkably lower limit of detection (LOD) value of 1.23 × 10^-7 M. 3 does not show sensing ability toward any NAC probably due to the coordination environment being different from those in 1 and 2. The work demonstrates fine-tuning of the topology and in turn magnetic and sensing properties by changing the reaction conditions.