Ligand-Exchange Processes on Solvated Beryllium Cations. Part III : Which Model Reaction is Preferable for Quantum-Chemical Investigations of a Water-Exchange Mechanism?
✍ Scribed by Ralph Puchta; Rudi van Eldik
- Publisher
- John Wiley and Sons
- Year
- 2008
- Tongue
- German
- Weight
- 314 KB
- Volume
- 91
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
On the basis of DFT calculations (B3LYP/6-311 þ G**), the possibility to include solvent effects is considered in the investigation of the H 2 O-exchange mechanism on [Be(H 2 O) 4 ] 2þ within the widely used cluster approach. The smallest system in the gas phase, [Be(H 2 O) 4 (H 2 O)] 2þ , shows the highest activation barrier of þ 15.6 kcal/mol, whereas the explicit addition of five H-bonded H 2 O molecules in [{Be(H 2 O) 4 (H 2 O)}(H 2 O) 5 ] 2þ reduces the barrier to þ 13.5 kcal/mol. Single-point calculations applying CPCM (B3LYP(CPCM:H 2 O)/6-311 þ G**//B3LYP/6-311 þ G**) on [Be(H 2 O) 4 (H 2 O)] 2þ lower the barrier to þ 9.6 kcal/mol. Optimization of the precursor and transition state of [Be(H 2 O) 4 (H 2 O)] 2þ within an implicit model (B3LYP(CPCM:H 2 O)/6-311 þ G** or B3LYP(PCM:H 2 O)/6-311 þ G**) reduces the activation energy further to þ 8.3 kcal/mol but does not lead to any local minimum for the precursor and is, therefore, unfavorable.