Page 81 - Book of Abstracts

th
8 Biannual Conference on Chemistry - CHEM 08

Theoretical X-ray Absorption L-edge Spectra of Manganese
Acetylacetonate Complexes

Nuha Bin Hameed, Walid Hassan, Shaaban Elroby and Rifaat Hilal
king abdulaziz university, Jeddah-21589 Saudi Arabia.
Email:nhameed0004@stu.kau.edu.sa.

ABSTRACT

The 3d transition metals play an important role in many charge transfer
processes in catalysis and biology (Kubin, Guo et al. 2018). X-ray absorption
spectroscopy at the L-edge of metal sites probes metal 2p−3d excitations,
providing key access to their valence electronic structure, which is crucial for
understanding these processes (Kubin, Guo et al. 2018). XAS spectra of TM
complexes contain a lot of chemical information, and a lot of efforts are needed
to explore its theoretical analysis (Carlotto, Sambi et al. 2017). Because of the
complex electronic structure of the final states, determined by electron–electron
repulsion and spin–orbit coupling (SOC) in 2p and 3d orbitals, advanced
theoretical methods are required to correlate the spectral shape with the
electronic structure of the system (Pinjari, Delcey et al. 2016). A variety of
methods have been designed to model L-edge XAS spectra, namely, the Bethe-
Salpeter equation, the multichannel multiple scattering method, and different
configuration interaction (CI) methods (Pinjari, Delcey et al. 2016). The CI-based
methods differ in the way they describe electron correlation, in the selection of
the electronic configurations, and in the treatment of SOC. The restricted active-
space (RAS) method is an ab initio method based on the multiconfigurational
self-consistent field approach (Pinjari, Delcey et al. 2016). In the complete active-
space (CAS) method, a full CI is performed among the active orbitals; however,
for simulations of X-ray spectra, it is more convenient to use the RAS method
and to restrict the number of excitations from the core orbitals (Pinjari, Delcey et
al. 2016). Herein, Ab initio restricted active space (RAS) theory has been used to
model 3 complexes Mn(acac)2 , Mn(acac)2.H2O and Mn(acac)3 L2,3-edges
absorption spectra with minimal active space. The three complexes have been
chosen due to their variety of geometries. The effect of optimization method as
well as the effect of solvation and basis set on the excitation energy was evaluated
for one complex, Mn(acac)3 to test their efficiency in reproducing experimental
features.

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