Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: Investigation of three different oxidation states relevant to the oxygen-evolving complex of Photosystem II
Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn KBeta X-ray emission spectroscopy (KBeta XES). The two manganese compounds are the di-(mu)-oxo compound [L'2MnIIIO2MnIVL'2](ClO4)3, where L' is 1,10-phenanthroline[Cooper, 1977 No.562] and the linear mono-(mu)-oxo compound [LMnIIIOMnIIIL](ClO4)2, where L- is the mono-anionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand[Horner, 1999 No.862]. Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the MnIVMnIV species for the di-(mu)-oxo compound and the MnIIIMnIV and MnIVMnIV species for the mono-(mu)-oxo compound. IR, UV/vis, EPR and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-(mu)-oxo and linear mono-(mu)-oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment. In contrast to Mn K-edge XANES, KBeta XES spectra show less dependence on ligand environment. The KBeta 1,3 peak energies are comparable for the di-(mu)-oxo and mono-(mu)-oxo compounds in equivalent oxidation states. The energy shifts observed due to oxidation are also similar for the two different compounds. The study of the different behavior of the XANES pre-edge and main-edge features in conjunction with KB eta XES provides significant information about the oxidation state and character of the ligand environment of manganese atoms.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Director, Office of Science. Office of Basic Energy Studies. Division of Energy Biosciences; National Institutes of Health (US)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 785258
- Report Number(s):
- LBNL-47212; JACSAT; R&D Project: 448135; TRN: AH200131%%230
- Journal Information:
- Journal of the American Chemical Society, Vol. 123, Issue 29; Other Information: Journal Publication Date: Jul. 25, 2001; PBD: 18 Dec 2000; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
X-RAY SPECTROSCOPY
EMISSION SPECTROSCOPY
MANGANESE COMPLEXES
MANGANESE COMPOUNDS
OXIDATION
VALENCE
SAMPLE PREPARATION
SPECTRA
LIGANDS
MN KB XES MN K-EDGE XANES MANGANESE ELECTROCHEMISTRY PHOTOSYSTEM II OXYGEN EVOLVING COMPLEX