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Which nido:nido-macropolyhedral boranes are most stable?
Farooq Ahmad Kiani1, Matthias Hofmann
1Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany.
Inorganic Chemistry
|August 15, 2006
Summary
Nido-borane clusters with up to 11 vertices are more stable than macropolyhedral boranes. However, anionic species and extra hydrogen atoms can shift stability preferences in these complex boron hydride clusters.
Area of Science:
- Computational chemistry
- Inorganic chemistry
- Boron hydride clusters
Background:
- Nido-borane clusters are a significant class of boron hydrides with diverse structures.
- Understanding the relative thermodynamic stabilities of different cluster arrangements is crucial for predicting their properties and reactivity.
- Macropolyhedral boranes, formed by linking smaller nido-borane units, present complex structural and stability considerations.
Purpose of the Study:
- To compare the relative thermodynamic stabilities of neutral and anionic nido-single clusters versus vertex-sharing nido:nido-macropolyhedral boranes.
- To investigate the influence of cluster size and hydrogen atom addition on stability preferences.
- To identify the most stable configurations for neutral and anionic nido:nido-macropolyhedral boranes.
Main Methods:
- Density functional theory (DFT) calculations using the RB3LYP functional.
- Utilized the 6-311+G(d,p) basis set for geometry optimization and frequency calculations, with 6-31G(d)+ZPE for energy computations.
- Systematic comparison of energies for nido-single clusters and nido:nido-macropolyhedral boranes.
Main Results:
- Neutral nido-single boranes with up to 11 vertices are more energetically favorable than isomeric macropolyhedral boranes.
- Extra hydrogen atoms on the open face significantly impact the stability comparison between single clusters and macropolyhedra.
- For anionic species, macropolyhedral preference emerges at 17 or more vertices.
- The most stable neutral and anionic nido:nido-macropolyhedral boranes typically comprise nido-10-vertex and nido-11-vertex units, respectively.
- Relative stabilities of isomeric neutral macropolyhedra correlate with the sum of individual cluster stabilities.
Conclusions:
- Nido-single boranes are generally more stable than macropolyhedral counterparts for smaller neutral systems.
- Anionic charge and hydrogen atom count are critical factors determining the stability landscape of boron hydride clusters.
- The findings provide insights into the structure-stability relationships of complex boron hydride systems, guiding future synthetic and theoretical studies.