The crystal and molecular structure of the boron trichloride complex of acetonitrile has been determined and that of the boron trifluoride complex redetermined. Least-squares refinement of three-dimensional X-ray data led to a conventional R factor on F of 3.9% for the BCl3 complex (441 nonzero reflections) and 5.6% for the BF3 complex (382 nonzero reflections). Both complexes crystallize in the space group D2h 16-Pnma of the orthorhombic system with four molecules in unit cells of dimensions a = 8.67 (1), b = 7.32 (1), and c = 10.19 (1) Å for Cl3BNCCH3 and a = 7.784 (3), b = 7.177 (3), and c = 8.360 (3) Å for F3BNCCH3. The calculated densities of 1.65 g/cm3 for Cl3BNCCH3 and 1.55 g/cm3 for F3BNCCH3 are in reasonable agreement with previously measured densities of 1.60 and 1.59 g/cm3, respectively. The molecules are required to have symmetry m. The configuration about the boron in each complex is nearly tetrahedral. The B-N bond length in the BCl3 complex (1.562 (8) Å) is significantly shorter than the B-N bond length in the BF3 complex (1.630 (4) Å). The X1-B-N and X2-B-N bond angles are, respectively, 105.3 (3) and 105.8 (2)° where X = F and 106.9 (3) and 106.7 (4)° where X = Cl. These results are rationalized in terms of a model for donor-boron halide interaction in which the acceptor strength of a boron halide increases with increasing distortion of the BX3 group. This model also is consistent with thermochemical and spectroscopic data on boron halide complexes.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry