Versatility of the nature of the magnetic Cu(ii)–U(iv) interaction. Syntheses, crystal structures and magnetic properties of Cu2U and CuU compounds

Abstract

Treatment of [M(H₂Lⁱ)] with U(acac)₄ in refluxing pyridine led to the formation of the trinuclear complexes [{MLⁱ(py)_x}₂U] [L¹ = N,N′-bis(3-hydroxysalicylidene)-2,2-dimethyl-1,3-propanediamine and M = Ni, Cu or Zn; L² = N,N′-bis(3-hydroxysalicylidene)-1,3-propanediamine and M = Cu or Zn; L³ = N,N′-bis(3-hydroxysalicylidene)-2-methyl-1,2-propanediamine and M = Ni, Cu or Zn; x = 0 or 1]. The dinuclear compounds [ML³(py)U(acac)₂] (M = Cu, Zn) were isolated from the reaction of [M(H₂L³)] and U(acac)₄ in pyridine at 60 °C. The crystal structures of the trinuclear complexes are built up by two orthogonal MLⁱ(py)_x units which are linked to the central uranium ion by the two pairs of oxygen atoms of the Schiff base ligand; the U(IV) ion is found in the same dodecahedral configuration but the Cu(II) ion coordination geometry and the Cu⋯U distance are different by passing from L¹ or L² to L³, due to the shortening of the diimino chain of L³. These geometrical parameters seem to have a great influence on the magnetic behaviour of the complexes since the Cu–U coupling in [{CuLⁱ(py)_x}₂U] (i = 1, 2) is ferromagnetic while it is antiferromagnetic in [{CuL³(py)_x}₂U]. In the compounds [{CuL³(py)_x}₂U] and [CuL³(py)U(acac)₂], the Cu coordination and the Cu⋯U distance are very similar, and both exhibit an antiferromagnetic interaction.