cis-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2, the poor relative betweencisandtranstautomers. A theoretical study of the gas-phase Fe L3-edge and C and O K-edge XAS oftrans-/cis-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2

The relative stability oftrans-[(η5-C5H5)Fe(η1-CO)(μ-CO)]2(trans-I) andcis-Itautomers in a vacuum and in solvents with different dielectric constants (ε) has been investigated by exploiting density functional theory (DFT). Theoretical results indicate that, in agreement with experimental evidence,trans-Iis more stable thancis-Iin a vacuum (∼1.5 kcal mol−1;ε= 1), while the opposite is true in media withε> 7. Differently from solution, DFT outcomes pertaining to the vapor-phasecis-I⇆trans-Iequilibrium at T = 368 K, the temperature at which the Fe L2,3-edges and the C and O K-edge X-ray absorption spectroscopy (XAS) data ofIhave been recorded, ultimately indicate thetrans-Ipredominance (∼93%). Compositions, oscillator strengths (f) and excitation energy (EE) values ofcis-Itransitions substantially mirror those oftrans-I; nevertheless, the weightedcis-If(EE) distributions negligibly contribute to the diverse simulated XA spectra ofI.