Structural and Energetic Properties of Haloacetonitrile-BCl3 Complexes: Computations and Matrix-IR Spectroscopy
James A Phillips1, Samuel J Danforth1, Nicholas J Hora1
1Department of Chemistry, University of Wisconsin-Eau Claire , Eau Claire, Wisconsin 54702, United States.
The Journal of Physical Chemistry. A
|November 15, 2017
Summary
Quantum-chemical computations and IR spectroscopy reveal two distinct structures for fluoroacetonitrile-boron trichloride and chloroacetonitrile-boron trichloride complexes, with experimental data supporting only the predicted short-bond structures.
Area of Science:
- Computational Chemistry
- Spectroscopy
- Inorganic Chemistry
Background:
- Boron trihalides are Lewis acids that readily form adducts with Lewis bases.
- Nitrile-boron trihalide complexes are of interest due to their unique bonding characteristics.
Purpose of the Study:
- To investigate the structural properties and bonding of fluoroacetonitrile-boron trichloride (FCH2CN-BCl3) and chloroacetonitrile-boron trichloride (ClCH2CN-BCl3) complexes.
- To compare theoretical predictions with experimental spectroscopic data.
Main Methods:
- Quantum-chemical computations using the M06-2X/aug-cc-pVTZ level of theory.
- Low-temperature matrix-isolation infrared (IR) spectroscopy using nitrogen matrices.
Main Results:
- Theoretical calculations predicted two stable equilibrium structures for both FCH2CN-BCl3 and ClCH2CN-BCl3 complexes, characterized by short (1.610 Å and 1.604 Å) and long (2.870 Å and 2.865 Å) B-N distances, respectively.
- The short-bond structures correspond to global energy minima with binding energies of 5.3 and 6.3 kcal/mol, while metastable long-bond structures have binding energies of 3.2 and 3.3 kcal/mol.
- Experimental IR spectra showed bands consistent with the predicted short-bond structures, with no evidence for the long-bond structures.
Conclusions:
- The study confirms the existence of two distinct structural configurations for FCH2CN-BCl3 and ClCH2CN-BCl3 complexes.
- Experimental spectroscopic evidence supports the theoretical prediction of short-bond structures as the dominant form under matrix-isolation conditions.
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