title: Vibrational circular dichroism spectroscopy of a spin-triplet bis-(biuretato) cobaltate(III) coordination compound with low-lying electronic transitions.
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.
authors.affiliation: Quantum Protein Centre, Department of Physics, Technical University of Denmark, DK-2800 Kgs, Lyngby, Denmark. christjo@fysik.dtu.dk
authors.forename: Christian
authors.initials: C
authors.lastname: Johannessen
authors.forename: Peter W
authors.initials: PW
authors.lastname: Thulstrup
mesh_terms: D016880:Anisotropy; D001737:Biuret / Q000031:analogs & derivatives* / Q000737:chemistry; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D004121:Dimethyl Sulfoxide; D004563:Electrochemistry; D007202:Indicators and Reagents; D008024:Ligands; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: C519275:1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyldodecanato(4-)cobaltate(III); D007202:Indicators and Reagents; D008024:Ligands; D009942:Organometallic Compounds; D001737:Biuret; D004121:Dimethyl Sulfoxide