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11:10
Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model
Published on: May 23, 2018
Charge distribution in chromium and vanadium catecholato complexes: X-ray absorption spectroscopic and computational
Carsten Milsmann1, Aviva Levina, Hugh H Harris
1Centre for Heavy Metals Research, School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
Inorganic Chemistry
|June 6, 2006
Summary
This study investigates redox-active transition-metal complexes, revealing that oxidation is primarily metal-based for chromium and vanadium triscatecholato complexes, but ligand-based for a chromium monocatecholato complex.
Area of Science:
- Bioinorganic Chemistry
- Materials Science
- Coordination Chemistry
Background:
- Transition-metal complexes with redox-active catecholato ligands serve as crucial models for bioinorganic systems.
- These complexes also hold potential for applications in molecular materials due to their tunable electronic properties.
Purpose of the Study:
- To investigate the electronic structures and oxidation behavior of chromium and vanadium catecholato complexes.
- To compare the metal- versus ligand-based oxidation pathways in mono- and triscatecholato systems.
- To elucidate the electron delocalization in various oxidation states using spectroscopic and computational methods.
Main Methods:
- X-ray absorption spectroscopy (XAS), including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (XAFS) analyses.
- Bulk electrolysis performed directly within the XAS cell to generate various oxidation states in solution.
- Density functional calculations to analyze electron-density distribution.
- X-ray crystallography to determine the molecular structure of a vanadium complex.
Main Results:
- XAS data indicate predominantly metal-based oxidations for both Cr(V/IV/III) and V(V/IV/III) triscatecholato complexes, evidenced by increased edge energies and M-O bond length contractions.
- Higher electron delocalization between metal and ligands was observed in chromium complexes compared to vanadium complexes.
- Oxidation of a Cr(III) monocatecholato complex was found to be ligand-based, forming a semiquinonato species, with no significant changes in XANES features and an increased Cr-O bond length.
Conclusions:
- The oxidation mechanism (metal-based vs. ligand-based) is dependent on the complex's structure (mono- vs. triscatecholato) and the metal ion (Cr vs. V).
- Electron delocalization plays a significant role in the redox properties of these transition-metal catecholato systems.
- Findings provide insights into the fundamental electronic behavior of redox-active coordination compounds relevant to bioinorganic chemistry and materials science.
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