Dissociation of Bipyridine and Coordination with Nitrosyl: Cyclometalated Ruthenium Nitrosyl Complex
A novel family of ruthenium nitrosyl complexes [Ru(bpy)(C∧N)(MeCN)NO](PF6)2 (2a–2e, bpy = 2,2′-bipyridine, HC∧N = 2-phenylpyridine and its derivatives) has been prepared by reacting cyclometalated ruthenium complexes [Ru(bpy)2(C∧N)][PF6] (1a–1e) with NO+, which were comprehensively characterized by mass, IR, NMR, and UV–vis spectra as well as the single-crystal X-ray structure determinations. Herein, the coordination geometry of Ru atoms in 2a–2e is a distorted octahedron and {RuII–NO+}6 is present in these complexes. Theoretical calculations suggest that the reactions involving dissociation of one bipyridine and coordination with NO+ proceed spontaneously (ΔG < 0) and the transformation from 1a–1e to the intermediates is dominated by substituents (ΔGRI varies from −1.19 to −1.53 eV), which influence the binding energy between Ru(II) and NO+ in complexes 2a–2e (−89.42 to −101.17 kcal/mol) and thus control the photorelease of NO on a certain scale. The weak absorption bands in the visible region could be attributed to the contribution of dπ(RuII) → π*(NO+), which were enhanced greatly under light, indicating the possible release of NO. The photoinduced NO, as well as singlet oxygen (1O2), was then confirmed by EPR spectra, and the amount of NO released from 2a–2e was estimated via Griess reagent assay. The cytotoxicity of these complexes with or without visible light irradiation was also investigated using an MTT assay.
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