Ligand field strengths of carbon monoxide and cyanide in octahedral coordination

Abstract

Ligand field splittings were extracted from absorption spectra of metal hexacarbonyl and hexacyano complexes over 35 years ago by Gray and coworkers (J. Am. Chem. Soc., 85, 2922 (1963); ibid. 90, 4260, 5713 (1968)). Recent time-dependent density functional theory calculations by Baerends and coworkers (J. Am. Chem. Soc., 121, 10356 (1999)) on M(CO)₆ with M = Cr, Mo, W raised questions about the magnitudes of these ligand field splittings. In order to reexamine such effects systematically, we report here the splittings for a series of 3d⁶ metal hexacarbonyl, hexaisocyano and hexacyano complexes:

, Cr(CO)₆,

and

;

and

; and

, Cr(CNH)₆,

and

. This work demonstrates that the 3d splittings induced by the ligands in question generally fall in the order CO > CNH > CN⁻. We agree with Baerends and colleagues that CO exerts a much stronger ligand field than was originally thought.

Keywords:

• Density functional theory
• Ligand field strength
• Carbon monoxide
• Cyanide
• Isocyanide

Acknowledgments

We thank the Caltech Summer Undergraduate Research Fellowship program as well as ONR-DURIP, ARO-DURIP, Beckman Institute, and NSF for support.

Notes

Dedicated to the memory of Founding Editor Art Martell.

Additional information

Notes on contributors

Harry B. Gray

Dedicated to the memory of Founding Editor Art Martell.