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

In this work, a series of three copper(II) metal-organic frameworks (MOFs), [Cu(4,4'-DP)Cl] n ( 1 ), [Cu(4,4'-DP) 0.5 Cl] n ( 2 ), and [Cu(4,4'-TMDP)Cl] n ( 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 fes , hcb , and sql topologies. On the other hand, 2 exhibits a bey (3,4-c net) topology and 3 shows 4-fold interpenetration with the dia 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 × 10 5 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.