Chirality determination in crystals.

This tutorial review article discusses chirality determination in the solid state, both in single crystals and in crystal assemblies, with an emphasis on X-ray diffraction. The main principles of using X-ray diffraction to reliably determine absolute structure are summarized, and the complexity which can be encountered in chiral structures-kryptoracemates, scalemates, and inversion twinning-is illustrated with examples from our laboratories and the literature. We then address the problem of the bulk crystallization and discuss different techniques to determine chirality in a large assembly of crystal structures, with a special prominence given to an X-ray natural circular dichroism mapping technique that we recently reported.

Validation of microscopic magnetochiral dichroism theory.

Magnetochiral dichroism (MChD), a fascinating manifestation of the light-matter interaction characteristic for chiral systems under magnetic fields, has become a well-established optical phenomenon reported for many different materials. However, its interpretation remains essentially phenomenological and qualitative, because the existing microscopic theory has not been quantitatively confirmed by confronting calculations based on this theory with experimental data. Here, we report the experimental low-temperature MChD spectra of two archetypal chiral paramagnetic crystals taken as model systems, tris(1,2-diaminoethane)nickel(II) and cobalt(II) nitrate, for light propagating parallel or perpendicular to the axis of the crystals, and the calculation of the MChD spectra for the Ni(II) derivative by state-of-the-art quantum chemical calculations.

Rapid Discrimination of Crystal Handedness by X-ray Natural Circular Dichroism (XNCD) Mapping.

An original method for determining the handedness of individual non-centrosymmetric crystals in a mixture using a tightly-focused, circularly polarized X-ray beam is presented. The X-ray natural circular dichroism (XNCD) spectra recorded at the metal K-edge on selected crystals of [Δ-M(en) ](NO ) and [Λ-M(en) ](NO ) (M=Co , Ni ) show extrema at the metal pre-edge (7712 eV for Co, 8335 eV for Ni). A mapping of a collection of some 220 crystals was performed at the respective energies by using left and right circular polarizations.

Resolution, structures, and vibrational circular dichroism of helicoidal trinickel and tricobalt paddlewheel complexes.

It has been recently shown that enantiomers of the helicoidal paddlewheel complex [Co (dpa) (CH CN) ] (dpa = the anion of 2,2'-dipyridylamine) can be resolved using the chiral [As (tartrate) ] anion (AsT) and that these complexes demonstrate a strong chiroptical response in the ultraviolet-visible and X-ray energy regions. Here we report that the nickel congener, [Ni (dpa) (CH CN) ] , can likewise be resolved using AsT. Depending on the stereochemistry of the enantiopure AsT anion, one or the other of the trinickel enantiomers crystallize from CH CN and diethyl ether in space group P42 2 as the (NBu ) [Ni (dpa) (CH CN) ](AsT) ·[solvent] salt.

Enantiopure Chiral Coordination Polymers Based on Polynuclear Paddlewheel Helices and Arsenyl Tartrate.

Herein, we report the preparation of chiral, one-dimensional coordination polymers based on trinuclear paddlewheel helices [M₃(dpa)₄] (M = Co(II) and Ni(II); dpa = the anion of 2,2'-dipyridylamine). Enantiomeric resolution of a racemic mixture of [M₃(dpa)₄] complexes was achieved by chiral recognition of the respective enantiomer by [Δ-As₂(tartrate)₂] or [Λ-As₂(tartrate)₂] in ,-dimethylformamide (DMF), affording crystalline coordination polymers formed from [(Δ-Co₃(dpa)₄)(Λ-As₂(tartrate)₂)]·3DMF (Δ-), [(Λ-Co₃(dpa)₄)(Δ-As₂(tartrate)₂)]·3DMF (Λ-), [(Δ-Ni₃(dpa)₄)(Λ-As₂(tartrate)₂)]·(4 - )DMF∙Et₂O (Δ-) or [(Λ-Ni₃(dpa)₄)(Δ-As₂(tartrate)₂)]·(4 - )DMF∙Et₂O (Λ-) repeating units. UV-visible circular dichroism spectra of the complexes in DMF solutions demonstrate the efficient isolation of optically active species.