15min:

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

We were surprised, thinking it might be a misprint, with such a short C-N bond length, 1.03(8) Å, of \hatX ⁶ FeNC when the Lie and Dagdigian paper (2001) on FeNC by LIF came out. Ziurys and Sheridan aslo found a short CN bond length for the \hatX CoCN, 1.13133 Å, by MW, last year. For \hatX ² _i NiCN, Kingston and Merer has reported a little short CN bond length of 1.1591(29) Å, determined by LIF, and Sheridan and Ziurys 1.1580(8) Å by MW. Our ab initio calculated r_e values, though some of them are preliminary at the moment, are 1.172 (FeNC), 1.171 (CoCN), and 1.166 Å (NiCN). The discrepancy between experimental and theoretical values is in the order FeNC > CoCN > NiCN, in parallel with the expected ionic character of the metal-ligand bond and accordingly with the floppy character of the bending motion. The observed too-short CN bond lengths in these radicals probably come from the inadequate model used for the analysis of observed spectra.

A new model will be proposed, and calculations of the three dimensional potential energy surfaces for \hatX ⁶ FeNC/FeCN , which are necessary for the theoretical analysis based on the new model, are in progress at the level of MR-SDCI+Q with Roos-ANO (Fe) and aug-cc-pVQZ (C and N) basis sets.