Direct Observation of Charge Transfer and Magnetism in Fe4Co4 Cyanide-Bridged Molecular Cubes.

We have studied the zero-dimensional cubane molecular correspondent of a Prussian blue analogue Cs-Fe4Co4 at low temperature and high magnetic field by means of L-edge X-ray absorption spectroscopy and X-ray magnetic circular dichroism. We probe the magnetic and electronic structures of Fe and Co separately upon light irradiation, which allows us to observe directly the electron transfer coupled to a spin transition phenomenon within the molecular cubes and to investigate the nature of the metastable photoexcited state. The magnetic moments in the photoexcited state are found to be M = 1.3μB ( Mspin = 0.59μB with large orbital moment, Morbit = 0.74μB) for low-spin FeIII and M = 1.5μB ( Mspin = 1.08μB with orbital moment, Morbit = 0.41μB) for high-spin CoII at 2 K and 6.8 T. From our results, we evidence that a strong antiferromagnetic coupling between the metal ions can be ruled out.