CHARACTERIZATION OF CHEMICAL-BONDS IN BIMETALLIC CYANIDES USING X-RAY-ABSORPTION SPECTROSCOPY AT L(2,3) EDGES

X-ray absorption spectroscopy at the L(2,3) edges of 3d transition met als has been used to study the electronic structure of molecular-based magnets with Curie temperatures ranging from 66 to 315 K. These magne ts are bimetallic cyanides of the Prussian blue family, constructed by a three-dimensional assembling of -NC-Cr-III-CN-A(II)-units. The chem ical selectivity of X-ray absorption spectroscopy allows information t o be extracted on each of the two different metal transition ions that carry the spin moments. Using Ligand Field Multiplet calculations, wh ere hybridization is mainly taken into account through configuration i nteraction, we have been able to reproduce nicely all the features of the divalent 3d ion L(2,3) edges. From the knowledge of the exact grou nd state, we have determined its electronic structure and relevant par ameters, such as the crystal field strength and the spin-orbit couplin g. We have separated covalence and charge transfer effects occurring i n the bond between the 3d ions and the cyano ligand. From the L(2,3) e dges of A(II) divalent ions, we found that the A(II)-NC bond has a wea k covalent character with a 10% charge transfer. From the Lr-2,Lr-3 ed ges of Cr-III, where Cr ions are bonded to the carbon atom of the cyan o ligand, we have shown that the Ligand Field Multiplet model is still fully applicable for strongly hybridized bonds. In this case it is es sential to separate between covalence and charge transfer and to take the charge transfer into account through pi back-bonding. The precise knowledge of these parameters is essential for the determination of ma croscopic characters like magnetic properties.