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

The iridium(iv) complex (NBu₄)₂[IrCl₆] (1) has been synthetised, characterised and used as a precursor to prepare the new chloro-bridged heterobimetallic Ir^IV-Cu^II chain of formula {IrCl₅(μ-Cl)Cu(viim)₄}_n (2) [viim = 1-vinylimidazole]. The crystal structure and magnetic properties of 1 and 2 have been investigated. Both compounds crystallise in the monoclinic system with space group C2/c. Each Ir^IV ion in both 1 and 2 is six-coordinate and bonded to six chloride ions in a regular octahedral geometry. In compound 2, the Cu^II ion exhibits an axially elongated octahedron with four N atoms, from four monodentate viim ligands, that form the equatorial plane, and two chloride ions that occupy the axial positions. The way in which the anionic [IrCl₆]^2- units are arranged in the crystal packing of 1, well separated from each other by means of the bulky NBu₄⁺ cations, avoids significant intermolecular Ir-ClCl-Ir interactions. The crystal lattice of 2 shows adjacent Ir^IV-Cu^II chains that are connected through ππ stacking interactions, and are organized adopting perpendicular arrangements. The study of the magnetic properties of 1 and 2 through dc magnetic susceptibility measurements reveals that 1 shows magnetic behaviour typical of noninteracting mononuclear centres with S = 1/2, whereas 2 exhibits ferromagnetic exchange coupling between the Cu^II and Ir^IV metal ions linked through chloride ligands. In addition, ac magnetic susceptibility measurements show a field-induced slow relaxation of the magnetisation for 1, indicating single-ion magnet (SIM) behaviour for this mononuclear Ir^IV system.