Knowledge Bank

Rotational spectra of the complex $HCN-BF3$ have been observed using pulsed nozzle Fourier transform microwave spectroscopy. Spectra have been observed for the $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}B$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}B$ species with both $HC14N$ and $HC15N$, and the hyperfine structure analyzed. The complex has the expected $C3v$ structure, with the nitrogen end of the HCN toward the boron, but the observed BN bond length of 2.54(6) \AA is notably shorter than that in the related weakly bound systems $N=N\equiv BF3$ and $N=C-C=N-BF3$. We compare the structure, energetics, force constants, and quadrupole coupling constants of the complex with those of other species formed from $BF3$ and nitrogen donors and extend our previous $discussion(1)$ of gas phase structure correlations as a means of mapping reaction paths for simple chemical transformations.