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Monoanionic molybdenum and tungsten tris(dithiolene) complexes: a multifrequency EPR study.
Stephen Sproules1, Priyabrata Banerjee, Thomas Weyhermüller
1Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany. sproules@mpi-muelheim.mpg.de
Inorganic Chemistry
|June 25, 2011
Summary
This study details molybdenum and tungsten tris(dithiolene) complexes, revealing distinct electronic structures based on ligand type. Electron paramagnetic resonance (EPR) spectroscopy differentiates between olefinic and aromatic dithiolene ligands, highlighting tungsten
Area of Science:
- Coordination Chemistry
- Organometallic Chemistry
- Spectroscopy
Background:
- Molybdenum (Mo) and tungsten (W) tris(dithiolene) complexes are versatile inorganic compounds with tunable redox properties.
- Understanding the electronic structures of these complexes is crucial for their application in catalysis and materials science.
Purpose of the Study:
- To synthesize and characterize Mo and W tris(dithiolene) complexes in various redox states.
- To elucidate the electronic structures of these complexes using crystallographic, electrochemical, and spectroscopic methods.
- To compare the electronic properties of Mo and W complexes and investigate the influence of dithiolene ligand type.
Main Methods:
- Synthesis and crystallographic characterization of [M(S(2)C(2)R(2))(3)](z) complexes (M = Mo, W; R = Ph, CN; z = 0, 1-, 2-).
- Cyclic voltammetry to determine redox potentials and reversibility.
- Multifrequency Electron Paramagnetic Resonance (EPR) spectroscopy (S-, X-, Q-band) for electronic structure analysis.
- Analysis of EPR spin-Hamiltonian parameters and comparison with electronic absorption spectra.
Main Results:
- Structural changes (bond lengths, angles) indicate ligand reduction upon complex reduction.
- Cyclic voltammetry shows two reversible redox couples (0/1- and 1-/2-).
- EPR spectroscopy reveals two distinct electronic structure types for monoanionic molybdenum complexes: [Mo(IV)((A)L(3)(5-•))](1-) (olefinic dithiolene) and [Mo(V)((B)L(3)(6-))](1-) (aromatic dithiolene).
- Tungsten complexes exhibit similar EPR parameters, with [W(bdt)(3)](1-) formulated as [W(V)((B)L(3)(6-))](1-) and [W((A)L(3))](1-) suggesting resonance forms involving W(IV) and W(V).
Conclusions:
- The electronic structure of Mo and W tris(dithiolene) complexes is strongly dependent on the dithiolene ligand type (olefinic vs. aromatic).
- EPR spectroscopy is a powerful tool for distinguishing these electronic structures.
- Tungsten shows a preference for higher oxidation states compared to molybdenum in related complexes.
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