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Pentavalent lanthanide nitride-oxides: NPrO and NPrO^- complexes with N≡Pr triple bonds.

ABSTRACT: The neutral molecule NPrO and its anion NPrO^- are produced via co-condensation of laser-ablated praseodymium atoms with nitric oxide in a solid neon matrix. Combined infrared spectroscopy and state-of-the-art quantum chemical calculations confirm that both species are pentavalent praseodymium nitride-oxides with linear structures that contain Pr≡N triple bonds and Pr=O double bonds. Electronic structure studies show that the neutral NPrO molecule features a 4f⁰ electron configuration and a Pr(v) oxidation state similar to that of the isoelectronic PrO₂⁺ ion, while its NPrO^- anion possesses a 4f¹ electron configuration and a Pr(iv) oxidation state. The neutral NPrO molecule is thus a rare lanthanide nitride-oxide species with a Pr(v) oxidation state, which follows the recent identification of the first Pr(v) oxidation state in the PrO₂⁺ and PrO₄ complexes (Angew. Chem. Int. Ed., 2016, 55, 6896). This finding indicates that lanthanide compounds with oxidation states of higher than +IV are richer in chemistry than previously recognized.

SUBMITTER: Hu SX

PROVIDER: S-EPMC5434915 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The chiral nonaazamacrocyclic amine L, which is a reduction product of the 3 + 3 Schiff base macrocycle, wraps around the lanthanide(III) ions to form enantiopure helical complexes. These Ce(III), Pr(III), Nd(III), Eu(III), Gd(III), Tb(III), Er(III), Yb(III) and Lu(III) complexes have been isolated in enantiopure form and have been characterized by spectroscopic methods. X-ray crystal structures of the Ln(III) complexes with L show that the thermodynamic product of the complexation of the RRRRRR-isomer of the macrocycle is the (M)-helical complex in the case of Ce(III), Pr(III), Nd(III) and Eu(III). In contrast, the (P)-helical complex is the thermodynamic product in the case of Yb(III) and Lu(III). The NMR and CD spectra show that the (M)-helicity for the kinetic complexation product of the RRRRRR-isomer of the macrocycle is preferred for all investigated lanthanide(III) ions, while the preferred helicity of the thermodynamic product is (M) for the early lanthanide(III) ions and (P) for the late lanthanide(III) ions. In the case of the late lanthanide(III) ions, a slow inversion of helicity between the kinetic (M)-helical product and the thermodynamic (P)-helical product is observed in solution. For Er(III), Yb(III) and Lu(III) both forms have been isolated in pure form and characterized by NMR and CD. The analysis of 2D NMR spectra of the Lu(III) complex reveals the NOE correlations that prove that the helical structure is retained in solution. The NMR spectra also reveal large isotopic effect on the 1H NMR shifts of paramagnetic Ln(III) complexes, related to NH/ND exchange. Photophysical measurements show that L(RRRRRR) appears to favor an efficient 3pipi*-to-Ln energy transfer process taking place for Eu(III) and Tb(III), but these Eu(III)- and Tb(III)-containing complexes with L(RRRRRR) lead to small luminescent quantum yields due to an incomplete intersystem crossing (isc) transfer, a weak efficiency of the luminescence sensitization by the ligand, and/or efficient nonradiative deactivation processes. Circularly polarized luminescence on the MeOH solutions of Eu(III) and Tb(III) complexes confirms the presence of stable chiral emitting species and the observation of almost perfect mirror-image CPL spectra for these compounds with both enantiomeric forms of L.

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Pentavalent lanthanide nitride-oxides: NPrO and NPrO^- complexes with N≡Pr triple bonds.

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Pentavalent lanthanide nitride-oxides: NPrO and NPrO- complexes with N≡Pr triple bonds.

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OmicsDI is part of the ELIXIR infrastructure

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Pentavalent lanthanide nitride-oxides: NPrO and NPrO^- complexes with N≡Pr triple bonds.