Shining light on the mixed-valency in the Creutz-Taube ion

The Creutz-Taube ion, [(NH3)5Ru-pyz-Ru(NH3)5]5+ (pyz = pyrazine) is the archetypal example of a mixed-valency system. The electrically neutral ligands result in five positive charges to be shared between two identical Ru sites. Interestingly, all experimental evidence suggests that the Ru sites are identical with an oxidation state of +2.5 and not a mixture of oxidation states +3 and +2. Surprisingly, this compound has never been studied by XANES and XMCD. Therefore, in this study, we propose to (1) directly assess the established conclusion of two identical Ru sites in the Creutz-Taube ion, and (2) determine the Ru magnetization from L2,3-edge XAS and XMCD at the ID12 beamline. These experiments will provide unprecedented insight into the electronic structure of the Creutz-Taube ion. These experiments on this bench-mark compound will be of fundamental importance for the understanding of mixed-valency which paves the way for new approaches to e.g. molecule-based magnetic conductors.