A neutral rhenium–biimidazole complex for the selective recognition of fluoride ions

The luminescent characteristics of neutral rhenium(I)-biimidazole complex combined with the hydrogen bonding ability of the coordinated biimidazole ligand permits it to selectively recognize fluoride ion among other halide ions, thereby enhancing its luminescence intensity. [Display omitted] •The rhenium complex 1 was synthesized by a simple one pot solvothermal synthesis.•Compound 1 contains both a recognition site and a signal output unit.•It selectively detects F– ion in the presence of other halide anions.•A significant luminescence enhancement was observed for 1 with F– ion. The neutral rhenium(I)-biimidazole complex [Re(CO)3(biimH)(1,4-NVP)] (1) was designed and synthesized by a one-pot reaction of Re2(CO)10, 2,2′-biimidazole (biimH2) and 4-(1-naphthylvinyl)pyridine (1,4-NVP). The structure of 1 was characterized by various spectroscopic techniques including IR, 1H NMR, FAB-MS, and elemental analysis and further confirmed by a single-crystal X-ray diffraction analysis. The mononuclear complex 1, a relatively simple structure with an octahedral geometry, is comprised of facial-arranged carbonyl groups, one chelated biimH monoanion, and one 1,4-NVP. Complex 1 shows the lowest energy absorption band at around 357 nm and an emission band at 408 nm in THF. The luminescent characteristics of 1 combined with the hydrogen bonding ability of the partially coordinated monoionic biimidazole ligand permits the complex to selectively recognize fluoride ions (F–) in the presence of other halides through a dramatic luminescence enhancement. The recognition mechanism of 1 can be convincingly explained in terms of H-bond formation and proton abstraction upon the addition of F– ions by 1H and 19F NMR titration experiments. The electronic properties of 1 were further supported by time dependent density functional theory (TDDFT) computational studies.