Cluster of Hexamolybdenum [Mo₆Cl₁₄]^2-for Sensing Nitroaromatic Compounds

This contribution describes a novel method for the detection of trace amounts of trinitrotoluene (TNT) using a cluster of hexamolybdenum with general formula [Mo6Cl14]2-. The molybdenum cluster was characterized by UV-visible, FT-IR, and fluorescence techniques, and the synthesis was efficient and reproducible. The evaluation of the molybdenum cluster by TNT detection was perfomed by fluoresecent measurements, and the results were interpreted by the Stern-Volmer equation, obtaining KSV values of 2.9 × 105 and 1.6 × 104 M-1 in different concentration ranges. Further, the results suggest that at TNT concentrations higher than 4 × 10-5 mM (0.01 mg L-1) it is possible to measure the quenching of the cluster fluorescence. The DFT calculations indicate that the contribution of the TNT in the active lowest unoccupied molecular orbitals that are involved in the higher intensity transitions in the complex cluster-TNT are significant. This situation differs from all the luminescent [M6X8L6]2- clusters (M = Mo; X = facial bridging ligand, and L = labile axial ligands), where most of the closely spaced excited states are located in the {M6X8}q+ core. Thus, the TNT switches off the cluster luminescence. The approach using a [Mo6Cl14]2-based fluorescence sensor has the potential to be a sensing technology for the detection of nitroaromatic explosives.