Elucidating the exchange interactions in a {(GdCu4II)-Cu-III} propellor

The multinucleating ligand 2,2 & PRIME;-(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 {LnCu(4)} four-blade propeller topology. We report the synthesis, structure and magnetic characterisation of [LnCu(4)(H4L)(4)](Cl)(2)(ClO4)middot6CH(3)OH, 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 H4L2- 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.