One-dimensional coordination polymers of [Co3(dpa)4](2+) and [MF6](2-) (M = Re(IV), Zr(IV) and Sn(IV))

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.

Coexistence of metamagnetism and slow relaxation of magnetization in ammonium hexafluoridorhenate

The (NH₄)₂[ReF₆] (1) salt was studied by X-ray diffraction, Raman spectroscopy, theoretical calculations, and magnetic measurements. 1 crystallizes in the trigonal space group P3̄m1 (Re-F = 1.958(5) Å). In the Raman spectrum of 1, splitting of the observed peaks was observed and correlated to the valence frequencies of vibration of the [ReF₆]^2- anion. The study of the magnetic properties of 1, through DC and AC magnetic susceptibility measurements, reveals the coexistence of metamagnetism and slow relaxation of magnetization at low temperature, which is unusual in the molecular systems based on the paramagnetic 5d metal ions reported so far.

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]2+ (M = Co(II) and Ni(II); dpa = the anion of 2,2'-dipyridylamine). Enantiomeric resolution of a racemic mixture of [M₃(dpa)₄]2+ complexes was achieved by chiral recognition of the respective enantiomer by [Δ-As₂(tartrate)₂]2- or [Λ-As₂(tartrate)₂]2- in N,N-dimethylformamide (DMF), affording crystalline coordination polymers formed from [(Δ-Co₃(dpa)₄)(Λ-As₂(tartrate)₂)]·3DMF (Δ-1), [(Λ-Co₃(dpa)₄)(Δ-As₂(tartrate)₂)]·3DMF (Λ-1), [(Δ-Ni₃(dpa)₄)(Λ-As₂(tartrate)₂)]·(4 - n)DMF∙nEt₂O (Δ-2) or [(Λ-Ni₃(dpa)₄)(Δ-As₂(tartrate)₂)]·(4 - n)DMF∙nEt₂O (Λ-2) repeating units. UV-visible circular dichroism spectra of the complexes in DMF solutions demonstrate the efficient isolation of optically active species. The helicoidal [M₃(dpa)₄]2+ units that were obtained display high stability towards racemization as shown by the absence of an evolution of the dichroic signals after several days at room temperature and only a small decrease of the signal after 3 h at 80 °C.

Temperature dependence of the spin state and geometry in tricobalt paddlewheel complexes with halide axial ligands

A series of tricobalt EMACs with halide axial ligands demonstrate diverse spin-crossover behaviors as a function of the molecular geometry and the nature of the axial ligand.