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Unexpectedly Lengthened N-H.Co Hydrogen Bonds?
Lee Brammer1, Juan C. Mareque Rivas, Dong Zhao
1Department of Chemistry, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, Missouri 63121-4499.
Inorganic Chemistry
|October 24, 2001
Summary
This study reveals that subtle changes in crystal structures significantly impact N-H.Co hydrogen bonds. Solid-state analysis shows these weak interactions are sensitive to supramolecular structure and intermolecular forces.
Area of Science:
- Organometallic chemistry
- Solid-state chemistry
- Supramolecular chemistry
Background:
- Intermolecular interactions, particularly hydrogen bonds, play a crucial role in determining the properties of chemical compounds.
- Understanding the factors influencing hydrogen bond geometry is essential for designing materials with specific characteristics.
- Previous studies have shown significant changes in N-H.Co hydrogen bond lengths with major alterations to the cation or anion.
Purpose of the Study:
- To investigate the effect of small, remote structural modifications on N-H.Co hydrogen bonding in organometallic salts.
- To compare solid-state and solution-state behavior of these hydrogen bonds.
- To elucidate the sensitivity of hydrogen bond geometry to supramolecular assembly.
Main Methods:
- Low-temperature X-ray crystallography to determine precise crystal structures.
- Nuclear Magnetic Resonance (NMR) spectroscopy to study interactions in solution.
- Infrared (IR) spectroscopy to analyze vibrational modes indicative of hydrogen bonding.
Main Results:
- Low-temperature crystal structures of quinuclidinium and 1,4-diazabicyclooctane salts with cobalt carbonyl anions were determined.
- Intermolecular N-H.Co hydrogen bonding was observed in the solid state for all studied salts.
- NMR and IR data confirmed the persistence of these hydrogen bonds in toluene solution.
- Solid-state N-H.Co hydrogen bonds in the new salts were found to be slightly longer than predicted based on solution behavior and related structures.
- Small changes to the anion or cation, remote from the hydrogen bond, had their effects subsumed by supramolecular structural changes in the solid state.
Conclusions:
- The geometry of N-H.Co hydrogen bonds is highly sensitive to the overall balance of intermolecular interactions in the solid state.
- Supramolecular structure significantly influences weak interactions, even when modifications are remote from the interaction site.
- These findings highlight the importance of crystallographic characterization for understanding weak intermolecular interactions.
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