Understanding the origin of CO oxidation activity at single Ru(II) site: a combined Ru L3 and Cl K edge RIXS study

Ru(II) compounds are widely used in catalysis. Here we have designed an air-stable surface -[bipy-Ru(II)(CO)2Cl2] site that is obtained by reduction of -[bipy-Ru(III)Cl4]- with simultaneous ligand exchange from Cl- to CO. The -[bipy-Ru(II)(CO)2Cl2] site enables oxidation of CO while the Ru(III) site is completely inert. This raises interesting questions on 1) why Ru(III) is not active; 2) the role of Cl and CO ligand in catalysis; 3) how O-O bond is split. Luckily, Ru L3 edge and Cl K edge are only 15 eV away from each other, motivating us for an in situ Resonant inelastic X-ray spectroscopy (RIXS) study of the molecular orbital configuration that allows characterization of the bonding of the ligands to Ru(II)/(III). This work contributes to the study of electronic structures of single-site catalysts at molecular level. With one excitation, both Ru and Cl emission can be observed. This principle can be utilized to study metals at interface for catalysis and energy systems.