The electronic structure and deexcitation pathways of an isolated metalloporphyrin ion resolved by metal L-edge spectroscopy

Kaja Schubert*, Meiyuan Guo, Kaan Atak, Simon Dörner, Christine Bülow, Bernd Von Issendorf, Stephan Klump, J. Tobias Lau, Piter S. Miedema, Thomas Schlathölter, Simone Techert, Martin Timm, Xin Wang, Vicente Zamudio-Bayer, Lucas Schwob, Sadia Bari

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The local electronic structure of the metal-active site and the deexcitation pathways of metalloporphyrins are crucial for numerous applications but difficult to access by commonly employed techniques. Here, we applied near-edge X-ray absorption mass spectrometry and quantum-mechanical restricted active space calculations to investigate the electronic structure of the metal-active site of the isolated cobalt(III) protoporphyrin IX cation (CoPPIX+) and its deexcitation pathways upon resonant absorption at the cobalt L-edge. The experiments were carried out in the gas phase, thus allowing for control over the chemical state and molecular environment of the metalloporphyrin. The obtained mass spectra reveal that resonant excitations of CoPPIX+ at the cobalt L3-edge lead predominantly to the formation of the intact radical dication and doubly charged fragments through losses of charged and neutral side chains from the macrocycle. The comparison between experiment and theory shows that CoPPIX+ is in a 3A2g triplet ground state and that competing excitations to metal-centred non-bonding and antibonding σ* molecular orbitals lead to distinct deexcitation pathways.
Original languageEnglish
Pages (from-to)3966-3976
JournalChemical Science
Volume12
Early online date3-Feb-2021
DOIs
Publication statusPublished - Mar-2021

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