Synthesis and structural and magnetic characterisation of copper(II) complexes of mixed phosphonate-antimonate ligands

A polynucleating oxygen donor ligand based on condensation of p-chlorophenylstibonic acid (ArSbO₃H₂) and t-butylphosphonic acid is reported. [(SbAr)₂O(HO₃P^tBu)₆] contains two antimony centres, bridged by an oxide and two hydrogen phosphonates. Reaction with copper acetate under solvothermal conditions produces four new polymetallic copper complexes. With pyridine used as a base the major product is a tetracopper cage, [Cu₄O₂(SbAr)₂(O₃P^tBu)₂(O₂CMe)₂(OMe)₆], with the four copper centres arranged in a rhombus; a minor product is a tricopper complex, [Cu₃O₄(SbAr)₂(O₃P^tBu)₄(py)₃]. With LiOMe as base the major product is again the tetranuclear cage, but the minor product is a heterometallic cage, [Cu₅Li₄O₆(SbAr)₄(O₃P^tBu)₆(O₂CMe)₂(OMe)₄ (MeOH)₄]. With 2,6-lutidine as base an octametallic complex is formed, [Cu₈O₄(SbAr)₂(O₃P^tBu)₆(O₂CMe)₄(lutidine)₂]. Magnetic studies show both anti-ferromagnetic and weak ferromagnetic exchange between the copper centres in these new complexes.