The toxic agrochemical contamination of food and the environment is one of the most pressing concerns for human health and environmental sustainability. In this work, a water-stable 3D lanthanidebased MOF, [Tb 2 (H 2 btec)(btec)(H 2 O)]•4H 2 O (Tb-MOF) has been demonstrated as a turn-off luminescent sensor for the detection of poisonous paraquat. The ligand 1,2,4,5-benzenetetracarboxylic acid (H 4 btec) was incorporated into Tb-MOF to act as a detection recognition site for a selective interaction with paraquat, resulting in a dramatic luminescence quenching. The obtained Tb-MOF not only is water stable but also tolerates acidic and basic conditions. On top of that, the rapid detection of paraquat in aqueous solution with high sensitivity and selectivity can be obtained even in the presence of common contaminants in the environment. The linear range for paraquat detection was observed in the concentration range from 0 to 50 μM with a low limit of detection of 2.84 μM and a high quenching constant of 3.95 × 10 4 M −1 . Tb-MOF can be applied to detect paraquat in water and agricultural samples with satisfactory recoveries from 85.59 to 105.20%. To gain insights into the molecular recognition, time-dependent density functional theory (TD-DFT) calculations were conducted to reveal the specific interactions between paraquat and the ligand in the backbone structure of the MOF. The quenching mechanism is attributed to a photoinduced electron transfer (PET) from the MOF to paraquat and the competitive absorption of excitation energy by paraquat. To demonstrate a practical implementation of the MOFbased sensor, a PVA/Tb-MOF@paper strip was fabricated, which can visually detect paraquat under irradiation with a UV lamp. These results indicate that Tb-MOF can be used as a potential sensor for the practical detection of paraquat in the environment and agricultural products.

Molecular devices based on spin-crossover (SCO) compounds are important targets for molecular electronics. In this study, six air-stable FeIII complexes have been prepared: [Fe­(naphBzen)2]Cl (1), [Fe­(naphBzen)2]­Cl·0.5hexane (1·0.5hexane); [Fe­(naphBzen)2]­Cl·2CHCl3·1.15hexane (1·2CHCl3·1.15hexane), [Fe­(naphBzen)2]Br (2), [Fe­(naphBzen)2]­Br·0.5hexane (2·0.5hexane), and [Fe­(naphBzen)2]­Br·2CHCl3 (2·2CHCl3). The hexane solvates are isostructural, crystallizing in the tetragonal space group I41/a. Weak van der Waals interactions between the cations result in the Fe1 and Fe2 centers packing into chiral chains and exhibiting two-step SCO. In contrast, the nonisostructural CHCl3 solvates have a single Fe center and crystallize in the triclinic space group P1̅ and are LS up to 350 K. The solvent-free systems are also not isostructural with [Fe­(naphBzen)2]­Cl, crystallizing in the triclinic space group P1̅, while [Fe­(naphBzen)2]Br undergoes a phase transition from tetragonal P43 to P43212 upon heating from 150 to 280 K. In both cases the compounds are trapped in the LS state. Magnetic data reveals that SCO occurs only in the hexane solvates, indicating that even very weak interactions can be critical in observing spin-crossover behavior.

A series of three solvates [Fe(naphPren)2]I·CH2Cl2 1, [Fe(naphPren)2]I·CHCl3 2 and [Fe(naphPren)2]I·acetone 3 with the novel ligand HnaphPren {2-([(2-(propylamino)ethyl]imino)methyl)naphthalen-2-ol} is reported. Magnetic studies of these complexes reveal that 1 exhibits an...