Vibrational circular dichroism spectroscopy of a spin-triplet bis-(biuretato) cobaltate(III) coordination compound with low-lying electronic transitions

Dalton Trans. 2007 Mar 14:(10):1028-33. doi: 10.1039/b618995d. Epub 2007 Jan 30.

Abstract

Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy was applied in the analysis of vibrational and low lying electronic transitions of a triplet ground state cobalt(III) coordination compound. The spectroscopic measurements were performed on the tetrabutylammonium salt of (6S,7S)-1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyl-dodecanato(4-)cobaltate(III) in DMSO solution and in potassium bromide pellets. The chiral anion exhibits an unusual geometry for cobalt(III), being four-coordinate, planar, and paramagnetic with an intermediate spin state. The spectroscopic results were compared to measurements performed on the free ligand and to theoretical calculations using density functional theory (B3LYP/TZVP). The results of the VCD analysis of the coordination compound identified an electronic, dipole-forbidden, magnetic dipole-allowed low-lying d-d transition located in the mid infrared, as well as several amide stretch transitions located in the fingerprint region (1800-1100 cm(-1)), in both the liquid and solid phase. VCD signals were found to be 5-10 times higher than expected, indicating enhancement of the vibrational CD signals, caused by coupling of the vibrational transitions with the close-lying electronic transition.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anisotropy
  • Biuret / analogs & derivatives*
  • Biuret / chemistry
  • Circular Dichroism*
  • Crystallography, X-Ray
  • Dimethyl Sulfoxide
  • Electrochemistry
  • Indicators and Reagents
  • Ligands
  • Models, Molecular
  • Organometallic Compounds / chemistry*
  • Spectroscopy, Fourier Transform Infrared

Substances

  • 1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyldodecanato(4-)cobaltate(III)
  • Indicators and Reagents
  • Ligands
  • Organometallic Compounds
  • Biuret
  • Dimethyl Sulfoxide