Dipyrrolyldiketone difluoroboron complexes:: Novel anion sensors with C-H•••X- interactions

1,3-Dipyrrolyl-1,3-propanediones, synthesized from pyrroles and malonyl chloride, form BF2 Complexes, which represent a new class of nakedeye sensors for halide and oxoanions. The association mode for the interactions of both the pyrrolyl NH and bridging CH protons with anions was confirmed by H-1 NMR chemical shifts in CD2Cl2 and supported by theoretical studies. The binding constants (K-a) were estimated as 8.1x10(4), 2.0x10(3), 3.3x10(2), 1.3x10(4), and 80m(-1) for F-, Cl-, Br-, H2PO4-, and HSO4- by UV/Vis absorption spectral changes in CH2Cl2. Augmentation of K. compared with dipyrrolylquinoxaline for H2PO4- is much larger than those for other anions. Contrary to other anions, F- quenches the emission almost completely, which was detected by the fluorescence spectrum as well as the naked-eye. In the case of the chloride anion complex, the formation of Cl-bridged 1D networks, in which anion is associated with two BF2 complexes, is observed in the solid state.