X-ray snapshots for metalloporphyrin axial ligation
- Chemical Sciences and Engineering Division
Axial ligation mechanisms of a metalloporphyrin, nickel(II) tetramesitylporphyrin (NiTMP), were investigated by static and transient X-ray absorption spectroscopy at Ni K-edge (8.333 keV). A surprisingly broad (i.e. {approx}1.4 eV) linewidth for the 1s {yields} 3d{sub x2-y2} transition in the ground state was attributed to strong geometry dependent 3d molecular orbital (MO) energies due to coexisting conformers in solution. The broad distribution of 3d MO energy levels enables transient degeneracy of the 3d{sub z2} and 3d{sub x2-y2} MOs to produce a temporary vacancy in the 3d{sub z2} MO which favors axial ligation. Photoexcitation also induces the vacancy in the 3d{sub z2} MO, leading to a more than two-fold enhancement in the axial ligated species. Therefore, a unified axial ligation mechanism for both the ground and excited state is proposed based on the elucidation of the excited state structural dynamics, which will have a broad impact in understanding and controlling axial ligation in enzymatic reactions and molecular catalysis involving transient axial ligation.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 1043153
- Report Number(s):
- ANL/CSE/JA-66840; TRN: US201213%%116
- Journal Information:
- Chemical Science, Vol. 1, Issue 5; ISSN 2041-6520
- Country of Publication:
- United States
- Language:
- ENGLISH
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