Elucidating the exchange interactions in a {GdCu} propellor.

The multinucleating ligand 2,2'-(propane-1,3-diyldiimino)bis[2-(hydroxymethyl)-propane-1,3-diol] (bis-tris propane, HL) is used in the design of a new family of 3d-4f complexes that display an unusual {LnCu} four-blade propeller topology. We report the synthesis, structure and magnetic characterisation of [LnCu(HL)](Cl)(ClO)·6CHOH, where Ln = Gd (1), Tb (2), Dy (3), La (4). Previously we have used CHCOO and NO as co-ligands with bis-tris propane, but here the use of Cl and ClO leads to coordination of four {Cu(HL)} units around the central Ln ion. A magneto-structural analysis reveals that the geometrical arrangement of the Cu(II) centres defined by the HL 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.