Replacing two chlorido ligands by a bipyridine ligand in ruthenium nitrosyl complexes with NO-release capabilities: A comparative study
Résumé
Ru-II(FT)(bipy)(NO)][PF6](3) [FT is the electron-rich 4'-(2-fluorenyl)-2,2': 6',2 ''-terpyridine ligand and bipy is 2,2'-bipyridine] is synthesized and characterized. It crystallizes in the triclinic P (1) over bar space group [a = 9.5362(2) angstrom, b = 10.3946(4) angstrom, c = 22.5701(8) angstrom, alpha = 94.7400(10)degrees, beta = 94.9400(10)angstrom, gamma = 101.0680(10)]. A photochemical study is presented in comparison with that of the parents cis(Cl, Cl)-[RuII(FT) Cl-2(NO)][PF6] and trans(Cl, Cl)-[RuII(FT) Cl-2(NO)][PF6]. The three derivatives release nitric oxide ((NO)-N-center dot) under irradiation at lambda = 405 nm with respective quantum yields of 0.06, 0.31, and 0.10. Their two-photon absorption (TPA) cross-sections (sTPA) were investigated by the Z-scan technique on related derivatives in which two hexyl chains were introduced to improve their solubility while their spectroscopic properties remained almost unaffected. The resulting sTPA values of 100 GM at. = 800 nm are in the window of transparency for human tissues, and the bipyridine-based complex exhibits a slight tendency for higher efficiency. The replacement of the [Ru-II(Cl)(2)(NO)] core by [Ru-II(bipy)(NO)] provides a much simpler synthesis, and the TPA-induced (NO)-N-center dot-release capabilities are in the same range of magnitude. Therefore, it is envisioned that (NO)-N-center dot donors of greater complexity with several metal centers could be investigated in future.