Structural and Energetic Properties of Haloacetonitrile–BCl3 Complexes: Computations and Matrix-IR Spectroscopy

The FCH2CN–BCl3 and ClCH2CN–BCl3 complexes were investigated by quantum-chemical computations and low-temperature, matrix-isolation-IR spectroscopy. Theory predicts two stable equilibrium structures, with distinctly different B–N distances, for both complexes. One set of structures, which correspond to the global energy minima, exhibit B–N distances of 1.610 and 1.604 Å for FCH2CN–BCl3 and ClCH2CN–BCl3, respectively (via M06-2X/aug-cc-pVTZ). The corresponding binding energies are 5.3 and 6.3 kcal/mol. For the metastable structures, the B–N distances are 2.870 and 2.865 Å for FCH2CN–BCl3 and ClCH2CN–BCl3, respectively, and the corresponding binding energies are 3.2 and 3.3 kcal/mol. Also, the barriers between these structures on the B–N distance potentials are 2.5 and 2.8 kcal/mol, respectively, relative to the secondary, long-bond minima. In addition, several IR bands of both FCH2CN–BCl3 and ClCH2CN–BCl3 were observed in nitrogen matrices, but the assigned bands are consistent with M06-2X predictions for the short-bond, minimum-energy structures. None of the observed IR bands could be assigned to the metastable, long-bond structures.