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Issue 11, 2018
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Unveiling controlled breaking of the mirror symmetry of Eu(fod)3 with α-/β-pinene and BINAP by circularly polarised luminescence (CPL), CPL excitation, and 19F-/31P{1H}-NMR spectra and Mulliken charges

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Abstract

We investigated whether the ‘Pfeiffer effect’ of optically inactive Eu(fod)3 (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) is detectable when it is dissolved in four chiral hydrocarbons, namely, (1S)-/(1R)-α-pinene, (1S)-/(1R)-β-pinene, (1S)-/(1R)-trans-pinane and (S)-/(R)-limonene. Among these solvents, α-pinene and β-pinene induced clear circularly polarised luminescence (CPL) signals in CPL-silent Eu(fod)3 at the electric dipole (ED)-forbidden/magnetic dipole (MD)-allowed 5D07F1 transition at 593 nm and the ED-allowed/MD-forbidden 5D07F2 transition at 613 nm due to Eu(III). The CPL excitation (CPLE) spectra monitoring the 5D07F1 and 5D07F2 transitions confirmed that these CPL bands are induced by the chirality of α-pinene. Eu(fod)3 in the presence of non-charged chiral aromatic additives, including (S)-/(R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP), (S)-/(R)-[1,1′-binaphthalene]-2,2′-diylbis[1,1-diphenyl-1,1′-phosphine-oxide] (BINAPO) and (S)-/(R)-α-phenylethylamine (PEA), also showed mirror-image CPL spectra with different extents of dissymmetry factors in their CPL signals. The 19F-NMR spectra revealed that the CPL signals had two different origins, which can be categorized as the Pfeiffer-perturbed system at an outer-sphere and a strong coordinative interaction at an inner-sphere Eu(III). The former was exemplified by α-pinene, BINAP and dilute PEA, whereas the latter was observed with BINAPO and neat PEA. The strong coordinative interaction of Eu(fod)3 with BINAPO was verified by comparing its 31P{1H}-NMR spectrum with that in the presence of BINAP. The Mulliken charges of Eu(fod)3 and the chiral compounds obtained with MP2(6-311G) calculations led us to hypothesize that the surplus charge neutralization can act as an invisible attractive force between several ligands in the Eu(III) complexes and CPL-inducible chiral compounds.

Graphical abstract: Unveiling controlled breaking of the mirror symmetry of Eu(fod)3 with α-/β-pinene and BINAP by circularly polarised luminescence (CPL), CPL excitation, and 19F-/31P{1H}-NMR spectra and Mulliken charges

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Publication details

The article was received on 31 May 2018, accepted on 18 Jul 2018 and first published on 19 Jul 2018


Article type: Research Article
DOI: 10.1039/C8QI00509E
Citation: Inorg. Chem. Front., 2018,5, 2718-2733
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    Unveiling controlled breaking of the mirror symmetry of Eu(fod)3 with α-/β-pinene and BINAP by circularly polarised luminescence (CPL), CPL excitation, and 19F-/31P{1H}-NMR spectra and Mulliken charges

    A. J. Jalilah, F. Asanoma and M. Fujiki, Inorg. Chem. Front., 2018, 5, 2718
    DOI: 10.1039/C8QI00509E

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