[CrIII8MII6]n+ (MII = Cu, Co) face-centred, metallosupramolecular cubes

Abstract

Four [Cr^III₈M^II₆]ⁿ⁺ (M^II = Cu, Co) coordination cubes of formulae [Cr₈Co₆L₂₄Cl₁₂] (1), [Cr₈Co₆L₂₄(SCN)₁₂] (2), [Cr₈Cu₆L₂₄(H₂O)₁₂](SO₄)₆ (3), and [Cr₈Cu₆L₂₄Cl₁₂] (4) (where HL is 1-(4-pyridyl)butane-1,3-dione), were synthesised using the [Cr^IIIL₃] metalloligand in combination with a variety of M^II salts. The metallic skeleton of each cage describes a cube in which the [Cr^IIIL₃] moieties occupy the eight vertices and the M^II ions lie at the centre of the six faces. The axial coordination sites of the M^II cations are occupied by either H₂O molecules or Cl⁻/SCN⁻ anions originating from the M^II salt used in the synthesis, resulting in neutral 1, 2 and 4 and the cage in 3 being a 12+ cation; the charge-balancing SO₄²⁻ anions accommodated both inside and outside the cube. Magnetic susceptibility and magnetisation measurements reveal weak exchange between nearest neighbour metal ions, mediated via the L⁻ ligands. The modular assembly of the cubes suggests that any combination of [M^IIIL₃] metalloligand and M^II salt will work, potentially resulting in an enormous family of supramolecular assemblies. The charge of the cubes is controlled by the nature of the ligand occupying the axial sites on the M^II ions, suggesting trivial ligand exchange may offer control over, amongst others, solubility, reactivity, post-synthetic modification and substrate specificity. The large internal cavities of the cubes also suggest host–guest chemistry may be a fruiful route to encapsulating magnetic and/or redox active guests which could be employed to control magnetic behaviour, and the construction of multifunctional materials.