Elucidating the exchange interactions in a {Gd^IIICu^II₄} propellor

The multinucleating ligand 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxymethyl)-propane-1,3-diol] (bis-tris propane, H₆L) is used in the design of a new family of 3d-4f complexes that display an unusual {LnCu₄} four-blade propeller topology. We report the synthesis, structure and magnetic characterisation of [LnCu₄(H₄L)₄](Cl)₂(ClO₄)·6CH₃OH, where Ln = Gd (1), Tb (2), Dy (3), La (4). Previously we have used CH₃COO^- and NO₃^- as co-ligands with bis-tris propane, but here the use of Cl^- and ClO₄^- leads to coordination of four {Cu(H₄L)} units around the central Ln ion. A magneto-structural analysis reveals that the geometrical arrangement of the Cu(II) centres defined by the H₄L^2- ligands controls the magnetic communication between the different metal centres. DFT calculations performed on the isotropic (Gd) and diamagnetic (La) systems 1 and 4 help to unravel the intriguing exchange interactions.