Knowledge Bank

Traditional twin jet deposition has been used in conjunction with matrix isolation for the investigation of reactive complexes of the boron trihalides. Codeposition of $BF3$ with either $NH3$ or $(CH3)2O$ at dilutions of up to 1/1/4000 gave rise to strong absorptions due to the 1:1 adduct. These adducts can be formed as well at room temperature, and the spectra were in good agreement, although the matrix spectra were much sharper. The codeposition of these two bases with samples of $Ar/BCl3$ at total dilutions of up to 1/1/2000 gave rise to a series of product bands, which have been assigned to the 1:1 adduct as well, marking the first time these adducts have been identified. A lowering of symmetry from $C3\upsilon$ to $Ca$ was observed going from the $BCl3\cdot NH3$ adduct to the $BCl3\cdot O(CH3)2$ adduct, as indicated by the splitting of the doubly degenerate $BCl3$ stretching mode. Complexes of $BBr3$ were detected as well, marking the first time these species have been isolated. In addition, the common usage of the $NH3$ symmetric deformation mode as an iodicator of relative Lewis acidities was tested. Finally, it was noted that the position of the symmetric C-O-C stretching mode of coordinated $(CH3)2O$ correlated well with Lewis acidity and may be used as an empirical measure as well.