Synthesis, crystal structures and thermal decomposition studies of a series of copper–lanthanoid complexes of 6-methyl-2-pyridone

Abstract

A series of mixed copper-Ianthanoid complexes have been synthesised and structurally characterised. All the compounds were made from the reaction of [Cu₆Na(mhp)₁₂]NO₃(mhp is the anion of 6-methyl-2-pyridone) with hydrated lanthanoid nitrates in methanol. In each case X-ray crystallographic analysis revealed a central Cu₂O₂ ring bridged to peripheral lanthanoid (Ln) atoms by mhp ligands. For early lanthanoids (La, Ce and Nd) the complex has a stoichiometry [Ln₂Cu₂(OMe)₂(mhp)₄(NO₃)₄(Hmhp)₂-(MeOH)₄], in which the Ln atoms are nine-co-ordinate, with approximate tricapped-trigonal prismatic, geometry. For later lanthanoids (Gd, Dy and Yb) the stoichiometry is [Ln₂Cu₂(OMe)₂(mhp)₄(NO₃)₄-(Hmhp)₂(MeOH)₂] and the Ln atoms are eight-co-ordinate, with a geometry that can be related to a dodecahedron. For Ln = Sm a disordered co-ordination sphere results, presumably caused by the intermediate ionic radius of Sm leading to very similar stabilities for the eight- and nine-co-ordinate structures. Thermal decomposition studies of these complexes have also been carried out which indicate that decomposition occurs initially to monometallic oxides or oxide carbonates, followed by production of the mixed-oxide phase Ln₂CuO₄(for Ln = La, Nd, Gd or Dy) or Ln₂Cu₂O₅(for Ln = Er or Yb). In most cases CuO is also found. All oxide and oxide-carbonate phases have been characterised by X-ray powder diffraction.