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Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
Published on: December 16, 2013
Polyhedral boranes and elemental boron: direct structural relations and diverse electronic requirements
E D Jemmis1, M M Balakrishnarajan
1School of Chemistry, University of Hyderabad, Hyderabad 500046, India. jemmis@uohyd.ernet.in
Journal of the American Chemical Society
|July 18, 2001
Summary
Elemental boron
Area of Science:
- Solid-state chemistry
- Boron chemistry
- Materials science
Background:
- Macropolyhedral boranes serve as molecular models for understanding elemental boron's electronic structure.
- The beta-rhombohedral polymorph of boron exhibits electron deficiency, posing challenges for structural stability.
- Existing electron-counting rules for boranes do not fully explain the electronic nature of elemental boron polymorphs.
Purpose of the Study:
- To elucidate the electronic and structural connections between macropolyhedral boranes and elemental boron.
- To analyze the electron deficiency in beta-rhombohedral boron using borane models.
- To understand the factors contributing to the stability of boron polymorphs.
Main Methods:
- Molecular fragments approach using boranes as model systems.
- Electronic structure calculations (Extended Hückel and B3LYP/6-31G).
- Nuclear independent chemical shift calculations.
- Analysis of X-ray structure studies.
Main Results:
- A B57H36 molecule model requires three additional electrons beyond standard borane rules, confirmed by calculations.
- The B57H36(3+) molecule exhibits aromaticity comparable to B12H12(2-).
- Disorder, including partial occupancies and interstitial atoms, is essential for electron sufficiency and stability in beta-rhombohedral boron.
Conclusions:
- The idealized beta-rhombohedral boron structure is unstable without disorder.
- Disorder ensures electron sufficiency, explaining the high thermodynamic stability of this boron polymorph.
- Understanding borane-elemental boron connections offers insights into boron-rich solids and their properties.
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