Credit: © 2009 Wiley

Supramolecular clusters built by connecting heterometallic complexes of 3d and 4f metals via organic bridges have been studied over the past few years, not only for their structures and formation processes, but also for their unusual magnetic properties.

Annie Powell and co-workers at the University of Karlsruhe in Germany, in collaboration with researchers from Moldova, France and Belgium, have now observed1 a dramatic change in the magnetic behaviour of heterometallic dinuclear units on linking them. Three copper–lanthanide complexes were attached to an aromatic ring to form a propeller-shaped hexanuclear compound, which can be either left- or right-handed. Two compounds with opposite orientations then self-assemble into a double-propeller-shaped dimer through π–π interactions of the central rings and intermolecular hydrogen bonds.

With dysprosium as the lanthanide, the magnetic behaviour of the dimer is dramatically different from that of the dinuclear building unit. Such a significant change cannot be accounted for by supramolecular magnetic interactions alone, and the coordination geometries around the metal centres are similar in both species. The magnetic properties of dysprosium are anisotropic, however, and this phenomenon seems to be caused by a reorientation of the magnetic axes of the copper–dysprosium units upon intra- and supramolecular linkage.