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Polymorphism of dimethylaminoborane N(CH3)2-BH2
Alexander Bodach1, Thomas Bernert1, Michael Fischer2
1Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr, 45470, Germany.
Dimethylaminoborane undergoes dehydrocoupling to form cyclic structures. This study determined the monoclinic crystal structure of dimethylaminoborane, revealing its phase transition behavior and energetic stability.
Area of Science:
- Inorganic Chemistry
- Crystallography
- Materials Science
Background:
- Dimethylamine-borane adducts are precursors to aminoboranes.
- Aminoboranes can form cyclic dimers or trimers with varying structures.
- Polymorphism in dimethylaminoborane affects its stability and properties.
Purpose of the Study:
- To investigate the dehydrocoupling of dimethylamine-borane.
- To determine the crystal structure of dimethylaminoborane polymorphs.
- To understand the phase transition behavior and energetic stability of dimethylaminoborane.
Main Methods:
- Synthesis of dimethylaminoborane via dehydrocoupling.
- X-ray diffraction analysis (powder and single-crystal).
- Differential scanning calorimetry (DSC) for phase transition studies.
Main Results:
- Dimethylaminoborane crystallizes as a dimer (triclinic) or trimer (orthorhombic).
- The trimeric, six-membered ring structure is energetically more stable due to denser packing.
- A phase transition from the triclinic to a monoclinic polymorph occurs above 290 K.
- The monoclinic crystal structure (space group C2/m) was determined from powder diffraction data.
Conclusions:
- The synthesis conditions dictate the crystalline form of dimethylaminoborane.
- The monoclinic polymorph represents a stable phase at higher temperatures.
- Understanding the polymorphism is crucial for controlling the properties of dimethylaminoborane.
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