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Updated: Jun 12, 2025
09:45
Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
10.3K
Reversible phase transition in
Christian Näther1, Artjom Businski2, Rainer Herges2
1Institut für Anorganische Chemie, Universität Kiel, Germany.
Summary
The crystal structure of C20H14N4O4 transitions from monoclinic to triclinic upon cooling below 180 K, forming a second domain. This reversible phase transition involves significant structural changes and is driven by temperature.
Area of Science:
- Crystallography
- Materials Science
- Solid-State Chemistry
Background:
- The crystal structure of C20H14N4O4 was previously determined at 220 K in the monoclinic space group P21/c.
- Disorder of methyl hydrogen atoms was noted in the room-temperature structure.
Purpose of the Study:
- To investigate the potential phase transition indicated by reflection splitting upon cooling.
- To characterize the structural changes occurring between room temperature and 90 K.
Main Methods:
- X-ray diffraction data collection at variable temperatures (room temperature down to 90 K).
- Twin refinement techniques to analyze the low-temperature crystalline phases.
- Analysis of unit-cell parameters and crystallographic space groups.
Main Results:
- A discontinuity in unit-cell volume was observed between 170 and 180 K, indicating a phase transition.
- Upon cooling, the crystal structure transforms to triclinic (space group P1) with two independent molecules.
- The transition is reversible upon reheating, with the structure returning to the monoclinic P21/c space group.
Conclusions:
- The title compound undergoes a reversible temperature-induced phase transition from monoclinic to triclinic symmetry.
- The transition involves the formation of an additional crystal domain and changes in molecular conformation and arrangement.
- The low-temperature triclinic phase exhibits two crystallographically independent molecules, while the high-temperature phase has one.
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