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Enantiomeric resolution and X-ray optical activity of a tricobalt extended metal atom chain

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Abstract

A simple procedure based on anion exchange was employed for the enantiomeric resolution of the extended metal atom chain (EMAC) [Co3(dpa)4(MeCN)2]2+. Use of the chiral salt (NBu4)2[As2(tartrate)2], (Λ-1 or Δ-1), resulted in the selective crystallization of the EMAC enantiomers as [Δ-Co3(dpa)4(MeCN)2](NBu4)2[Λ-As2(tartarte)2]2, (Δ-2) and [Λ-Co3(dpa)4(MeCN)2](NBu4)2[Δ-As2(tartrate)2]2 (Λ-2), respectively, in the P4212 space group, whereas a racemic mixture of 1 yielded [Co3(dpa)4(MeCN)2][As2(tartrate)2]·2MeCN (rac-3), which crystallized in the C2/c space group. The local electronic and magnetic structure of the EMAC enantiomers was studied, exploiting a variety of dichroisms in single crystals. A strong linear dichroism at the Co K-edge was observed in the orthoaxial configuration, whereas it vanished in the axial orientation, thus spectroscopically confirming the D4 crystal symmetry. Compounds Δ-2 and Λ-2 are shown to be enantiopure materials as evidenced by mirror-image natural circular dichroism spectra in the UV/vis in solution and in the X-ray range at the Co K-edge in single crystals. The surprising absence of detectable X-ray magnetic circular dichroism or X-ray magnetochiral dichroism signals at the Co K-edge, even at low temperature (3 K) and a high magnetic field (17 T), is ascribed to a strongly delocalized spin density on the tricobalt core.

Graphical abstract: Enantiomeric resolution and X-ray optical activity of a tricobalt extended metal atom chain

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Publication details

The article was received on 21 Sep 2017, accepted on 04 Dec 2017 and first published on 04 Dec 2017


Article type: Edge Article
DOI: 10.1039/C7SC04131D
Citation: Chem. Sci., 2018, Advance Article
  • Open access: Creative Commons BY-NC license
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    Enantiomeric resolution and X-ray optical activity of a tricobalt extended metal atom chain

    A. Srinivasan, M. Cortijo, V. Bulicanu, A. Naim, R. Clérac, P. Sainctavit, A. Rogalev, F. Wilhelm, P. Rosa and E. A. Hillard, Chem. Sci., 2018, Advance Article , DOI: 10.1039/C7SC04131D

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