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TOO SHORT CN BOND LENGTHS EXPERIMENTALLY FOUND IN COBALT CYANIDE: AN AB INITIO MOLECULAR ORBITAL STUDY.

REI OKUDA, TSUNEO HIRANO AND UMPEI NAGASHIMA, Grid Technology Research Center, Institute of Advanced Industrial Science and Technology, 6-9-3 Ueno, Taito-ku, Tokyo 110-0015, Japan.

In the previous Ohio meeting, we pointed out that the CN bond lengths experimentally found for FeNC, CoCN, and NiCN are too-short. The CN bond lengths in these radicals found by spectroscopy are shorter in this order than those predicted by high-level 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) Å. Our r_e value for the CN bond predicted at the level of the MR-SDCI+Q+Relativistic-correction/Roos ANO(Co, C, N) is 1.171 Å, which is in the normal range observed and predicted for many CN-containing molecules. The difference in r₀ and r_e shows how floppy CoCN is for the bending vibration mode.