Double Exchange in 1D Chains

Double exchange was first found in manganese perovskites and then in iron-sulfur electron transfer proteins. In their mixed-valence forms (i. e. exhibiting metal ions of different oxidation states) the excess electron on the reduced ion is delocalized. This delocalization stabilizes a parallel spin alignment of the core spins. The result is a very strong, effective ferromagnetic coupling, which is difficult to achieve by other mechanisms.

A good delocalization in mixed-valence systems requires a short metal-metal distance, affording a direct d-d orbital overlap. In order to enforce short metal-metal distances, we are developing ligand systems where the octahedrally coordinated metal ions are bridged in a face-sharing fashion. The resulting short metal-metal distances of 2.5-2.7 Å indeed enable a delocalization via a direct d-d orbital overlap providing a delocalized mixed-valence ground state that enforces effective ferromagnetic high-spin groundstates.

The final goal is to extend this to one-dimensional chains of face-sharing octahedra, where in mixed-valence states the excess electron is spin-polarized delocalized over the whole one-dimensional chain (molecular spintronics) resulting in a ferromagnetic state.

• B. Sonnenburg, I. Liratzis, A. Stammler, H. Bögge, and T. Glaser
  "The First Heterotrinuclear Confacial Trioctahedron Ni^IITi^IVCr^III: Rational Modular Assembly and Cooperative Effects""
  Eur. J. Inorg. Chem., 2015, 912-915.