Versatility of the nature of the magnetic Cu(II)-U(IV) interaction. Syntheses, crystal structures and magnetic properties of Cu2U and CuU compounds

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,Nʹ-bis(3 -hydroxysalicylidene)-2,2-dimethyl-1,3-propanediamine and M = Ni, Cu or Zn; L2=N,Nʹ-bis(3-hydroxysalicylidene)-1,3-propanediamine and M = Cu or Zn; L3=N,Nʹ-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.