One- and Two-Photon-Induced Photochemistry of Iron Pentacarbonyl [Fe(CO)(5)]: Insights from Coupled Cluster Response Theory

Malcomson, Thomas and McKinlay, Russell G. and Paterson, Martin J. (2019) One- and Two-Photon-Induced Photochemistry of Iron Pentacarbonyl [Fe(CO)(5)]: Insights from Coupled Cluster Response Theory. CHEMPHOTOCHEM, 3 (9). pp. 825-832. ISSN 2367-0932

Abstract

We present herein the first comprehensive study of the one‐ and two‐photon absorption of Fe(CO)5 utilising a hierarchy of linear‐ and quadratic‐response coupled cluster (LR‐ and QR‐CC) methodologies to provide an in‐depth characterisation, as well as potential energy curves for axial and equatorial bond dissociations, highlighting the state crossings leading from the bright 1A2′′ state through to the dissociative 1E′ state. We have characterised a range of metal‐to‐ligand charge transfer (MLCT) and ligand field (LF) states that are in agreement with both previous studies and experiment, including the identification of a series of E′ states that present Rydberg character in the 5.9–7.2 eV region. Due to the rapid excited state dissociation of Fe(CO)5 through the low lying 1E′ and 2E′′ ligand‐field states, we have also included an LR‐CCSD analysis of the major dissociative product, Fe(CO)4. Analysis of the C2v geometry of Fe(CO)4 reveals four accessible ligand field states at 1.085, 1.684, 1.958, and 2.504 eV respectively, reinforcing the highly unstable nature of Fe(CO)4 along with a strong MLCT band between 4.300 and 5.573 eV. This band overlaps with one in the spectra of Fe(CO)5 suggesting that full fragmentation could proceed by two paths: two‐photon excitation leading to dissociation, or through sequential one‐photon absorption events, the first causing dissociation to and the second initiating further fragmentation of the complex.