The pH-dependent reversible cyclometallation and reactions with nitrite in a near-aqueous system of a related set of cyclometallated ruthenium(II) bipyridyl complexes were investigated in detail. These complexes are [Ru(ppy)(bpy)2]PF6 (1, bpy = 2,2′-bipyridine, Hppy = 2-phenylpyridine), [Ru(thpy)(bpy)2]PF6 (2, Hthpy = 2-(2-thienyl)pyridine), and [Ru(dfppy)(bpy)2]PF6 (3, Hdfppy = 2-(2,4-difluorophenyl)pyridine). As expected, reversible UV–Vis spectra of these three complexes in near-aqueous solutions can be achieved by treating with acid or base, which indicates a pH-dependent reversible cyclometallation. However, the addition of nitrite to acidic solutions of these complexes disturbed the reversible pH-dependent processes. Unexpected ruthenium complexes in the aforementioned system were then isolated and characterized using FT-IR, MS, 1H NMR, and UV–Vis spectra, indicating that two reaction modes occurred at the ruthenium(II) centers: (1) the insertion of NO into the ruthenium–aryl bond to form a ruthenium C-nitroso complex; and (2) the coordination of NO with the entire dissociation of one bipyridine to form a {Ru–NO}6 complex, which is the first example involving the cleavage of Ru–N∧N bonds in ruthenium bipyridyl complexes.

•A novel RuO2/NaBi(MoO4)2 nanoplates were synthesized.•The sensor based on RuO2/NaBi(MoO4)2 shows selective gas-sensing properties to H2S.•The RuO2 introducing increased the response of the sensors.The NaBi(MoO4)2 nanoplates and RuO2/NaBi(MoO4)2 composites were synthesized by hydrothermal processes. XRD, SEM, TEM were employed to determine their phase composition and morphology, and the specific surface areas were obtained by BET. The results showed the NaBi(MoO4)2 nanoplates were tetragonal scheelite phase with average crystalline size of 25 nm. The NaBi(MoO4)2 nanoplates and RuO2/NaBi(MoO4)2 composites were fabricated into gas sensors, and the gas-sensing results showed that the sensors were highly sensitive and selective to H2S, especially the sensor of 1 wt% RuO2/NaBi(MoO4)2. The sensing response of 1 wt% RuO2/NaBi(MoO4)2 sensor was 19 to 5 ppm H2S, 6.4-fold higher than that of pure NaBi(MoO4)2 sensor, the sensor also showed a fast response time of 11 s and a short recovery time of 4 s at 370 °C. Therefore, the RuO2/NaBi(MoO4)2 could be a promising candidate material for fast detection of H2S.

The pH-dependent reversible cyclometallation and reactions with nitrite in a near-aqueous system of a related set of cyclometallated ruthenium(II) bipyridyl complexes were investigated in detail. These complexes are [Ru(ppy)(bpy)2]PF6 (1, bpy = 2,2′-bipyridine, Hppy = 2-phenylpyridine), [Ru(thpy)(bpy)2]PF6 (2, Hthpy = 2-(2-thienyl)pyridine), and [Ru(dfppy)(bpy)2]PF6 (3, Hdfppy = 2-(2,4-difluorophenyl)pyridine). As expected, reversible UV–Vis spectra of these three complexes in near-aqueous solutions can be achieved by treating with acid or base, which indicates a pH-dependent reversible cyclometallation. However, the addition of nitrite to acidic solutions of these complexes disturbed the reversible pH-dependent processes. Unexpected ruthenium complexes in the aforementioned system were then isolated and characterized using FT-IR, MS, 1H NMR, and UV–Vis spectra, indicating that two reaction modes occurred at the ruthenium(II) centers: (1) the insertion of NO into the ruthenium–aryl bond to form a ruthenium C-nitroso complex; and (2) the coordination of NO with the entire dissociation of one bipyridine to form a {Ru–NO}6 complex, which is the first example involving the cleavage of Ru–N∧N bonds in ruthenium bipyridyl complexes.