Molecular and electronic structure of a ruthenium polypyridyl cyanide complex: Insights from X-ray crystallography and soft X-ray spectroscopies

Abstract

ARTICLE INFOKeywords: Ru polypyridine complex Single Crystal XRD Electronic structure XASABSTRACTThe structural and electronic properties of the ruthenium complex [Ru(tpy)(H2dcb)CN] [PF6] (tpy = 2,2′,2′’- terpyridine, H2dcb = 4,4′-dicarboxy-2,2′-bipyridine) were investigated using a combination of single-crystal X- ray diffraction (SCXRD), X-ray and UV photoelectron spectroscopy (XPS and UPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations. The molecular structure exhibits a distorted octahedral coordination geometry around the Ru(II) center, with coordination by tpy, H2dcb, and cyanide ligands. Crys- tallographic data reveal deprotonation of one carboxylic acid group and the formation of supramolecular dimers via hydrogen bonding and π-stacking interactions. XPS confirms the Ru²⁺ oxidation state and indicates full protonation of the carboxylic groups in the polycrystalline powder and UPS probes the energy of the highest occupied electronic state. N K-edge XAS measurements, supported by time-dependent DFT (TDDFT) calculations, reveal that unoccupied states are dominated by ligand-centered π* orbitals and metal-centered Ru 4d eg orbitals. Ru M2,3-edge XAS further supports the assignment of Ru 4d states and highlights the role of metal–ligand in- teractions in the electronic structure. These results provide a detailed understanding of the structural and electronic properties of this Ru(II) complex, relevant for its potential application in light-harvesting and electron- transfer systems.