RESUMEN
For its important roles in biology, nitrogen monoxide (·NO) has become one of the most studied and fascinating molecules in chemistry. ·NO itself acts as a "noninnocent" or "redox active" ligand to transition metal ions to give metal-NO (M-NO) complexes. Because of this uncertainty due to redox chemistry, the real description of the electronic structure of the M-NO unit requires extensive spectroscopic and theoretical studies. We previously reported the Ni-NO complex with a hindered N3 type ligand [Ni(NO)(L3)] (L3- denotes hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate anion), which contains a high-spin (hs) nickel(II) center and a coordinated 3NO-. This complex is very stable toward dioxygen due to steric protection of the nickel(II) center. Here, we report the dioxygen reactivity of a new Ni-NO complex, [Ni(NO)(I)(L1â³)], with a less hindered N2 type bis(pyrazolyl)methane ligand, which creates a coordinatively unsaturated ligand environment about the nickel center. Here, L1â³ denotes bis(3,5-diisopropyl-1-pyrazolyl)methane. This complex is also described as a hs-nickel(II) center with a bound 3NO-, based on spectroscopic and theoretical studies. Unexpectedly, the reaction of [Ni(NO)(I)(L1â³)] with O2 yielded [Ni(κ2-O2N)(L1â³)2](I3), with the oxidation of both 3NO- and the I- ion to yield NO2- and I3-. Both complexes were characterized by X-ray crystallography, IR, and UV-Vis spectroscopy and theoretical calculations.
RESUMEN
Electrostatic interactions between a quaternary pyridyl-ß-diketonate and anionic charged nanosheets were observed to produce a highly emissive dispersion in a rich water solution. A greater fluorescence quantum yield of approximately 50% was obtained when a luminogenic ß-diketonate, 1-(4-methoxyphenyl)-3-(3-hydroxyethyl-pyridinium bromide)-1,3-propandione (prepared by the Claisen condensation reaction and subsequent quaternization), was molecularly dispersed and enclosed by a couple of atomically flat ultrathin (approximately 1.0 nm) silicate sheets of anionic layered clay. By accommodating ß-diketonate into a narrow interlamellar space (approximately 0.4 nm distance), the molecular motion was suppressed, as confirmed by a smaller non-radiative relaxation rate constant, which was obtained by time-resolved luminescence and quantum yield measurements. Because the dense packing of ß-diketonate quenched the excited state, the isolation of luminogens by the co-adsorption of photochemical inert cations (tetramethylammonium and benzylammonium) was prevented by concentration quenching. A lower quantum yield was obtained by expanding the interlayer distance above 1.0 nm by co-adsorbing a photo-inactive water-soluble polymer, poly(vinylpyrrolidone). Therefore, the fixation and spatial separation of ß-diketonate in the narrow interlayer space was determined to be essential for obtaining strong emission.
RESUMEN
The iron(II)-nitroxyl complex [Fe(NO)(L3)] (1) (with L3- = a hindered hydrotris(pyrazolyl)borate ligand), a high-spin (hs)-{FeNO}8 complex in the Enemark-Feltham notation, is surprisingly stable and is the first of its kind that could be structurally characterized. We further studied this compound using a variety of spectroscopic methods. These results indicate a hs iron(II) center with a bound 3NO- ligand where the spins are antiferromagnetic coupled ( St = 1). Vibrational data show that this complex has a very strong Fe-NO bond. DFT calculations support this result and link it to very strong π-donation from the 3NO- ligand to the iron(II) center. Furthermore, a very unusual equilibrium between the hs-{FeNO}8 complex and a dinitrosyl iron complex (DNIC) of {Fe(NO)2}9 type is observed. The O2 reactivity of the complex is finally reported.
RESUMEN
The cobalt-nitrosyl complex [Co(NO)(L3)] is supported by a highly hindered tridentate nitrogen ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3-), and shows a linear Co-N-O unit. This complex was prepared by the reaction of the potassium salt of L3- with the cobalt-nitrosyl precursor [Co(NO)2(tmeda)](BPh4) (tmeda = N,N,N,'N'-tetramethylethylenediamine). The obtained cobalt-nitrosyl complex as well as the corresponding products from the reaction with dioxygen, [Co(η2-O2N)(L3)] and [Co(η2-O2NO)(L3)], were characterised by X-ray crystallography and a number of spectroscopic methods including IR/far-IR, UV-Vis, and NMR spectroscopy. We also performed MCD measurements and DFT calculations to further elucidate the electronic structure of [Co(NO)(L3)] and the optical properties of the complex. The MCD spectra reveal two NO-to-Co charge-transfer transitions with strong excited state displacements that give rise to vibrational progressions in the MCD spectra, indicative of a very covalent Co-NO bond. These results provide new insight into the properties of the Co-NO bond and the electron distribution in the complex, which is best described as [CoII(NO-)(L3)].