Rational Self‐Assembly of Tricobalt Extended Metal Atom Chains and [MF 6 ] 2– Building Blocks into One‐Dimensional Coordination Polymers

A new family of one-dimensional bromo-bridged Ir(IV)-Cu(II) complexes based on the hexabromoiridate(IV) metalloligand

By using the iridium(IV) complex (NBu₄)₂[IrBr₆] (1) as a metalloligand towards a Cu(II) metal ion, three novel Ir(IV) one-dimensional (1D) compounds of formula {IrBr₅(μ-Br)Cu(Meim)₄}_n (2), {IrBr₅(μ-Br)Cu(Viim)₄}_n (3) and {IrBr₅(μ-Br)Cu(Buim)₄}_n (4), [Meim = 1-methylimidazole; Viim = 1-vinylimidazole; Buim = 1-butylimidazole] have been prepared and structurally and magnetically characterised. Compounds 2, 3 and 4 crystallise in the triclinic, monoclinic and orthorhombic crystal systems with space groups P1̄, C2/c and Pccn, respectively. Each Ir(IV) ion in 1-4 is six-coordinate and bonded to six bromide ions in a quasi regular octahedral geometry. In compounds 2-4, the Cu^II ion shows an axially elongated octahedron with four N atoms, from four monodentate imidazole derivative ligands, that form the equatorial plane and two bromide ions that occupy the axial positions. Cu(II) and Ir(IV) ions are linked through bridging bromide anions generating Ir(IV)-Cu(II) chains [with intrachain Cu(II)⋯Ir(IV) distances covering the range of ca. 5.10-5.42 Å]. In the crystal lattice of 2 and 3 are observed significant intermolecular Ir-Br⋯Br-Ir contacts and π⋯Br interactions, which organize arrangements that contribute to stabilizing the crystal structure of these Ir(IV)-based compounds. DC magnetic susceptibility measurements reveal that 1 displays magnetic behaviour typical of noninteracting mononuclear centres with S = 1/2. Besides, antiferromagnetic behaviour (2 and 3) and ferromagnetic (4) exchange coupling occur between the Cu(II) and Ir(IV) metal ions in the one-dimensional bromo-bridged compounds 2-4. Moreover, the study of the AC magnetic susceptibility shows a field-induced slow relaxation of the magnetisation for 1, indicating the presence of the single-ion magnet (SIM) phenomenon for the magnetically isolated hexabromoiridate(IV) complex.

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.

Ferromagnetic exchange interaction in a new Ir(iv)–Cu(ii) chain based on the hexachloroiridate(iv) anion

The new chloro-bridged heterobimetallic Ir^IVCu^II chain of formula {IrCl₅(μ-Cl)Cu(viim)₄}_n [viim = 1-vinylimidazole] is the first reported compound based on the Cu^II and Ir^IV metal ions.

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.