Comparative Experimental and Theoretical Study of the C and O K-Edge X-ray Absorption Spectroscopy in Three Highly Popular, Low Spin Organoiron Complexes: [Fe(CO)], [(η-CH)Fe(CO)(μ-CO)], and [(η-CH)Fe]

The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)], [(η-CH)Fe(CO)(μ-CO)], and [(η-CH)Fe]; , , and , respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L-edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. 2019, 58, 5844). The first-principle simulation of the C and O K-edge features allowed us to univocally identify the electronic states associated to the ligand-to-metal charge transfer (LMCT) transitions both in and in . At variance to that, LMCT transitions with sizable oscillator strengths do not play any role in determining neither the C nor the O K-edge spectral pattern of . The higher π-acceptor capability of the CO ligand, regardless of its terminal or bridging coordination, with respect to [(η-CH)] is herein ultimately confirmed.