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

The relative stability of trans-[(eta(5)-C5H5)Fe(eta(1)-CO)(mu-CO)](2) (trans-I) and cis-I tautomers in a vacuum and in solvents with different dielectric constants (epsilon) has been investigated by exploiting density functional theory (DFT). Theoretical results indicate that, in agreement with experimental evidence, trans-I is more stable than cis-I in a vacuum (similar to 1.5 kcal mol(-1); epsilon = 1), while the opposite is true in media with epsilon > 7. Differently from solution, DFT outcomes pertaining to the vapor-phase cis-I ⇆ trans-I equilibrium at T = 368 K, the temperature at which the Fe L-2,L-3-edges and the C and O K-edge X-ray absorption spectroscopy (XAS) data of I have been recorded, ultimately indicate the trans-I predominance (similar to 93%). Compositions, oscillator strengths (f) and excitation energy (EE) values of cis-I transitions substantially mirror those of trans-I; nevertheless, the weighted cis-If(EE) distributions negligibly contribute to the diverse simulated XA spectra of I.

Automated summary

Using density functional theory, the relative stability of two tautomers in solvents with different dielectric constants was studied. It was found that trans-I is more stable in a vacuum, while cis-I is more stable in media with epsilon > 7. Experimental data at 368K also indicate trans-I predominance.