Knowledge Bank

In the previous Ohio meeting, we pointed out that the CN bond lengths experimentally found for FeNC, CoCN, and NiCN are too-short.}, RF05 (2004).} The CN bond lengths in these radicals found by spectroscopy are shorter in this order than those predicted by high-level \textit{ab initio} molecular orbital calculations. The tendency is in parallel with the expected ionicity for the metal-N or metal-C bond, and hence is in parallel with the floppiness in bending motion. Recently submillimeter spectra of $X~3\Phi i$ has been published by Sheridan, Flory, and Ziurys, and the CN bond length $r0$ derived for the $X~3\Phi \Omega =4$ is reported to be 1.1313(10) {\AA}.}., \textbf{121}, 8360-8368 (2004).} Our $re$ value for the CN bond predicted at the level of the MR-SDCI+Q+Relativistic-correction/Roos ANO(Co, C, N) is 1.171 {\AA}, which is in the normal range observed and predicted for many CN-containing molecules. The difference in $r0$ and $re$ shows how floppy CoCN is for the bending vibration mode.