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Discontinuum between a thiolate and a thiol ligand.
Danny G McGuire1, Masood A Khan, Michael T Ashby
1Department of Chemistry and Biochemistry, The University of Oklahoma, Norman, Oklahoma 73019, USA.
Inorganic Chemistry
|April 16, 2002
Summary
Hydrogen bonding to organometallic complexes has a continuous effect on thiolate ligand properties, but protonation causes a significant electronic structure change. This study investigates these effects on iron-thiolate compounds using computational and experimental methods.
Area of Science:
- Organometallic Chemistry
- Computational Chemistry
- Chemical Physics
Background:
- The electronic structure and reactivity of organometallic complexes are influenced by ligand interactions.
- Hydrogen bonding and protonation can significantly alter the properties of metal-ligand systems.
- Understanding these effects is crucial for designing new catalysts and materials.
Purpose of the Study:
- To investigate the effects of hydrogen bond donation and protonation on the electronic structure of (eta(5)-C(5)H(5))Fe(CO)(2)SR complexes.
- To elucidate the differences between continuous hydrogen bonding effects and discontinuous protonation effects.
- To correlate structural and electronic changes with the basicity of the thiolate ligand and the hydrogen bond donor.
Main Methods:
- Density Functional Theory (DFT) calculations were employed to study the electronic structures of the complexes and their hydrogen-bonded adducts.
- Single-crystal X-ray crystallography was used to determine the structural changes upon protonation.
- Infrared spectroscopy, monitoring carbonyl stretching frequencies, was used to assess the donor ability of the thiolate ligand.
Main Results:
- DFT calculations revealed that hydrogen bond donation to the thiolate ligand has a minor effect on the complex's electronic structure, while protonation leads to significant reorganization.
- Protonation results in a shift of the highest occupied molecular orbital (HOMO) character from sulfur to the iron center.
- X-ray crystallography confirmed a reduction in Fe-S bond distances upon protonation, indicating diminished Fe-S pi-antibonding.
- Carbonyl stretching frequencies showed that hydrogen bonding has a continuous effect, while protonation causes a discontinuous change.
Conclusions:
- Hydrogen bonding to the thiolate ligand in (eta(5)-C(5)H(5))Fe(CO)(2)SR complexes exerts a continuous influence on the ligand's donor properties, dependent on the hydrogen bond donor's pKa.
- Protonation of the thiolate ligand results in a discontinuous and more pronounced effect on the electronic structure and Fe-S bonding.
- The extent of the continuous effect of hydrogen bonding is limited, approximately 30% of the effect observed upon full protonation.