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Dramatic structural effects of a single hydrogen atom in HNPBu t 3
Sarah L Hinchley1, Mairi F Haddow, David W H Rankin
1School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, Scotland, U.K.
Inorganic Chemistry
|August 31, 2004
Summary
The molecular structure of tri-tert-butylphosphine imide was refined using the DYNAMITE method. This revealed significant deviations from symmetry and a shorter P-N bond, suggesting a double bond character.
Area of Science:
- Inorganic Chemistry
- Crystallography
- Computational Chemistry
Background:
- Tri-tert-butylphosphine imide (HNPBu(t)(3)) is a molecule with potential applications in various chemical processes.
- Previous structural determinations may have relied on simplifying symmetry assumptions.
- Understanding the precise molecular geometry is crucial for predicting chemical behavior.
Purpose of the Study:
- To re-determine the molecular structure of tri-tert-butylphosphine imide with high accuracy.
- To investigate the impact of the imide hydrogen on the molecule's symmetry.
- To refine the P-N bond length and assess its electronic character.
Main Methods:
- Utilized the DYNAMITE (Direct Analysis of Molecular Interatomic Distances and Torsions) method for structural refinement.
- Removed assumptions of local symmetry to allow for more accurate geometric parameters.
- Employed ab initio methods to validate findings regarding methyl group asymmetry.
Main Results:
- The DYNAMITE method allowed for the removal of local symmetry constraints without excessive parameter increase.
- Significant deviations from C(3) symmetry were observed in the NPBu(t)(3) group due to the imide hydrogen.
- N-P-C and C-P-C bond angles deviated from ideal symmetry, indicating a shift towards C(s) symmetry for the NPC(3) fragment.
- Methyl groups were found to be asymmetric, consistent with ab initio calculations.
- A significantly shorter P-N bond length was determined compared to previous studies.
Conclusions:
- The re-determination using the DYNAMITE method provides a more accurate molecular structure of tri-tert-butylphosphine imide.
- The observed structural features support a description of the molecule as HN=PBu(t)(3) rather than HN(-)-P(+)Bu(t)(3), indicating significant double bond character in the P-N bond.