Issue 5, 2018

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

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

Supplementary files

Article information

Article type
Edge Article
Submitted
21 Sept. 2017
Accepted
04 Dec. 2017
First published
04 Dec. 2017
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2018,9, 1136-1143

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, 9, 1136 DOI: 10.1039/C7SC04131D

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