Synthesis, crystal structures and properties of six cubane-like transition metal complexes of di-2-pyridyl ketone in gem-diol form

Abstract

Six cubane-type complexes comprising similar [M₄O₄]ⁿ⁺ cores [M = Mn(II), Co(II), Ni(II), Zn(II) or Cd(II)] synthesised in a facile route utilizing the gem-diol form of di-2-pyridyl ketone as a ligand have been characterised by X-ray structural analysis. Complex 1 crystallizes in the cubic space group I 3d, which is the highest symmetry documented in the cubane-like manganese compounds to date, while the other complexes crystallize in much lower crystallographic symmetries. The four metal ions and bridging alkoxo oxygen atoms are located at alternating vertices of a cube, with either pyridyl, acetate or aqua groups on the exterior of the core. Variable temperature magnetic susceptibility measurements indicate the presence of an antiferromagnetic behavior in 2 and ferromagnetic behaviors in 3 and 6. The temperature dependence of the magnetic susceptibility for 6 was fitted with J₁ = 6.04 cm⁻¹, J₂ = −1.47 cm⁻¹, and g = 2.12. The difference in sign between the J₁ and J₂ superexchange interactions is in good agreement with the different types of faces present in this Ni₄O₄ cubane core. Both 4 and 5 show similar ambient and cryogenic temperature emissions in solid state.