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Large gas-solid structural differences in complexes of haloacetonitriles with boron trifluoride
James A Phillips1, Jason A Halfen, John P Wrass
1Department of Chemistry, University of Wisconsin-Eau Claire, 105 Garfield Avenue, Eau Claire, WI 54701, USA. phillija@uwec.edu
Inorganic Chemistry
|January 18, 2006
Summary
Structural differences between gas-phase and solid-state halogenated acetonitrile-boron trifluoride complexes were observed. Crystallization significantly strengthens the boron-nitrogen dative bonds, particularly for fluoro- and chloro-derivatives.
Area of Science:
- Solid-state chemistry
- Computational chemistry
- Crystallography
Background:
- Acetonitrile-boron trifluoride (CH(3)CN-BF(3)) complexes are model systems for studying dative bonding.
- Halogenation of acetonitrile can influence the electronic and structural properties of these complexes.
- Understanding gas-phase versus solid-state structures is crucial for predicting material properties.
Purpose of the Study:
- To investigate the structural properties of singly halogenated acetonitrile-boron trifluoride derivatives (X-CH(2)CN-BF(3): X = F, Cl, Br, I).
- To compare the structural differences between the gas-phase and solid-state forms of these compounds.
- To elucidate the effect of halogen substitution on the boron-nitrogen dative bond strength.
Main Methods:
- Single-crystal X-ray crystallography was employed to determine solid-state structures.
- Solid-state infrared (IR) spectroscopy provided insights into vibrational modes.
- Correlated electronic-structure theory (B3PW91/aug-cc-pVTZ) was used for gas-phase calculations.
Main Results:
- Gas-phase calculations reveal weak B-N dative bonds (e.g., 2.422 Å for FCH(2)CN-BF(3)).
- Gas-phase B-N bond distances slightly strengthen from F- to Br-CH(2)CN-BF(3).
- Solid-state X-ray structures show significantly shorter B-N distances (approx. 1.65 Å), indicating a substantial strengthening upon crystallization, especially for F- and Cl-derivatives.
Conclusions:
- A large discrepancy exists between the gas-phase and solid-state structures of halogenated acetonitrile-boron trifluoride complexes.
- Crystallization dramatically enhances the B-N dative bond strength, evidenced by shorter bond lengths and shifts in vibrational frequencies.
- The observed structural changes highlight the significant influence of the solid-state environment on chemical bonding.
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