Cages on a plane: a structural matrix for molecular ‘sheets’

Abstract

A family of heterometallic Anderson-type ‘wheels’ of general formula [M^III₂M^II₅(hmp)₁₂]⁴⁺ (M^III = Cr or Al and M^II = Ni or Zn, Hhmp = 2-pyridinemethanol) has been extended to include M^III = Cr or Al and M^II = Co, Fe, Mn or Cu, affording five new species of formulae [Cr₂Co₅(hmp)₁₂](ClO₄)₄ (1), [Cr₂Fe₅(hmp)₁₂](ClO₄)₄ (2), [Cr₂Mn₅(hmp)₁₂](ClO₄)₄ (3), [Cr₂Cu₅(hmp)₁₂](ClO₄)₂(NO₃)₂ (4) and [Al₂Co₅(hmp)₁₂](ClO₄)₄ (5). As per previous family members, the metallic skeleton common to the cations of 1–5 describes a centred hexagon with the two M^III sites disordered around the outer wheel, with the exception of compound 4 where the Cu^II sites are localised. A structurally related, but enlarged planar disc possessing a [M^III₆M^II] hexagon capped on each edge by a Cu^II ion can be formed, but only when M^III = Al and M^II = Cu. In [Al^III₆Cu^II₇(OH)₁₂(hmp)₁₂](ClO₄)₆(NO₃)₂ (6) the Anderson moiety contains a central, symmetry-imposed octahedral Cu^II ion surrounded by a wheel of Al^III ions. Solid-state dc susceptibility and magnetisation measurements reveal the presence of competing exchange interactions in 1–5, and very weak antiferromagnetic exchange between the Cu^II ions in 6 which may be intra- and/or intermolecular in nature.