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Variable-temperature crystal structure studies of m-nitroaniline.
1Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wyb. Wyspiańskiego 27, 50-370 Wroclaw, Poland. wojcik@kchf.ch.pwr.wroc.pl
Summary
m-Nitroaniline exhibits a glass transition around 130 K due to freezing molecular motions. Above 340 K, plasticity leads to a probable second-order phase transition, preserving hydrogen bonds despite increased nitro group motion.
Area of Science:
- Solid-state chemistry
- Crystallography
- Materials science
Background:
- Understanding molecular behavior in crystals is crucial for materials design.
- Phase transitions and molecular dynamics influence material properties.
Purpose of the Study:
- To investigate the temperature-dependent crystal structure and phase transitions of m-nitroaniline.
- To elucidate the molecular mechanisms underlying observed thermal anomalies.
Main Methods:
- X-ray diffraction analysis across a temperature range (90-350 K).
- Calculation of thermal expansion coefficients and rigid-body analysis (translation and libration tensors).
- Analysis of intermolecular distances and molecular motion (torsion, libration, translation).
Main Results:
- Observed anomalies in lattice parameters at 110 K and 300 K.
- Identified a glass transition around 130 K, linked to freezing of molecular librations and translations.
- Detected a probable second-order phase transition above 340 K, characterized by increased plasticity, nitro group torsion, and preserved hydrogen bonds.
Conclusions:
- m-Nitroaniline undergoes distinct phase transitions influenced by molecular dynamics.
- The study reveals complex thermal behavior, including a glass transition and a high-temperature plastic phase with reorienting aggregates.