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New Osmocene and Ruthenocene Phases Reveal the Common Conformational Behavior Regulated by Anagostic Bonds in
Ida Moszczyńska1, Marek Szafrański2, Andrzej Katrusiak1
1Department of Materials Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Uniwersytetu Poznańskiego 8, 61-614 Poznań, Poland.
The Journal of Physical Chemistry Letters
|June 3, 2025
Summary
Ruthenocene and osmocene transform into higher-symmetry phases at specific temperatures. This reveals dynamic disordering of cyclopentadienyl rings, challenging previous assumptions about these metallocenes.
Area of Science:
- Organometallic Chemistry
- Solid-State Chemistry
- Crystallography
Background:
- Ruthenocene and osmocene were considered prototypical metallocenes, exclusively adopting the eclipsed conformation.
- This contrasts with ferrocene, known for its diverse polymorphic forms and conformations.
- Understanding metallocene conformational behavior is key to their chemical properties.
Purpose of the Study:
- To investigate the high-temperature phase transitions of ruthenocene and osmocene.
- To elucidate the conformational changes and structural dynamics in these metallocenes.
- To explore the role of intramolecular anagostic bonds in metallocene phase behavior.
Main Methods:
- Single-crystal X-ray diffraction studies at variable temperatures.
- Analysis of entropy changes during phase transitions.
- Fourier transform analysis of diffraction data.
- Calculation of electron density distribution from refined atomic displacement parameters.
Main Results:
- Ruthenocene and osmocene undergo phase transitions at 394.0 K and 421.5 K, respectively, forming higher-symmetry phases.
- In these new phases, cyclopentadienyl rings exhibit dynamic disordering via seesaw tilts and rotations.
- Molecules are disordered between staggered and eclipsed conformations, indicated by continuous electron density.
- A common transformation pattern linked to the breaking of intramolecular anagostic bonds (CH···M) was observed.
Conclusions:
- Ruthenocene and osmocene exhibit conformational flexibility and phase transitions not previously recognized.
- The strength of anagostic bonds correlates with the critical temperatures of these phase transitions.
- These findings provide a common framework for understanding phase transitions in prototypical metallocenes.
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