The first colorimetric receptor for the B4O72− anion based on nitro substituted phenanthroimidazole ferrocene derivatives

Four phenanthroimidazole ferrocene derivatives (2a–2d) were designed, synthesized and characterized by 1H NMR, 13C NMR and high-resolution mass spectroscopy (HRMS). Recognition of 12 anions by 2a–2d was investigated by UV-Vis absorption analysis, showing that 2b and 2d sensed B4O72− selectively among the tested anions with an obvious color change observed. 1H NMR titrations and theoretical calculations demonstrated that 2b binds B4O72− through O⋯H hydrogen bonding and O⋯B interactions between the nitro moiety and the B4O72− anion.