title: Quantum chemical and matrix-IR characterization of CH3CN-BCl3: a complex with two distinct minima along the B-N bond potential.
abstract: We have characterized the structural and energetic properties of CH3CN-BCl3via computations and matrix-IR spectroscopy. We find two equilibrium structures of the complex via computations. At the MP2/aug-cc-pVTZ level, the global minimum energy structure has a B-N distance of 1.601 Å, and a binding energy of 12.0 kcal mol(-1). The secondary structure lies 7.1 kcal mol(-1) higher in energy with a B-N distance of 2.687 Å and a binding energy of 4.9 kcal mol(-1). Computational scans of the B-N potential curve using both DFT and post-HF methods indicate that a significant barrier exists between these structures, and that it lies 1 to 2 kcal mol(-1) above the secondary minimum at a B-N distance of about 2.2 Å. We also observed several key, structurally-sensitive IR bands for six isotopic forms of the complex in neon matrices, including: the B-Cl asymmetric stretching band (ν) at 792 cm(-1) and the C-N stretching band (νCN) at 2380 cm(-1) (for the primary isotopomer, CH3C(14)N-(11)BCl3). These frequencies are consistent with computational predictions for the minimum-energy form of the complex. Energy decomposition analyses were conducted for CH3CN-BCl3 and also two related complexes, CH3CN-BF3 and CH3CN-BH3. These provide insight into the trend in Lewis acidity of the BX3 acceptors toward nitriles. Furthermore, these analyses indicate that the barrier along the B-N potential of CH3CN-BCl3 results from Pauli repulsion between the π electrons on the nitrile moiety and the chlorine atoms in BCl3, which is significant at relatively long distances where attractive bonding interactions fail to overcome it.
authors.affiliation: Department of Chemistry, University of Wisconsin Eau-Claire, Eau Claire, WI 54702, USA. phillija@uwec.edu.
authors.forename: John P
authors.initials: JP
authors.lastname: Wrass
authors.forename: Daniel
authors.initials: D
authors.lastname: Sadowsky
authors.forename: Kaitlin M
authors.initials: KM
authors.lastname: Bloomgren
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Cramer
authors.forename: James A
authors.initials: JA
authors.lastname: Phillips
mesh_terms: D001880:Boranes / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D003486:Cyanides / Q000737:chemistry*; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared / Q000379:methods*
chemical_list: D001880:Boranes; D002712:Chlorides; D003486:Cyanides; C092267:boron trichloride