Knowledge Bank

Earlier work on trimethylamine-boron halide $complexes1$ has been extended to include the $BI2$ complex and deuterium and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}N$ isotopic substitution. Single crystal X-ray diffraction determinations have been carried out on the chloro-, bromo-, and iodo- adducts to provide crystal structures and molecular parameters. Although the crystal structures of these compounds differ from that of the $BF3$ adduct, the molecular structure is essentially the same. Moreover, for all complexes, it was possible to differentiate unequivocally the molecular $A1$ and E modes by means of polarized infrared studies of oriented crystals. Normal coordinate calculations have been carried out for a seventeen atom molecule having $C3v$ symmetry using data from five isotopic species obtained by substitution of $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B$ for $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B,15N$ for $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}N$, and D for H. The experimental and computational results have yields a frequency assignment which has a relatively small degree of uncertainty for the fundamentals less than $1600cm-1$. Numerical results will be presented and discussed. Raman spectra of isotopic species of liquid and gaseous trimethylamine have been obtained and a new frequency assignment is proposed consistent with the new experimental data and the frequency assignment for the above complexes.