Theoretical study of oxocarbons: structure and vibrational spectrum of the D6h and C2 forms of the rhodizonate ion

Abstract

The molecular properties of the rhodizonate ion in the D 6h planar and C 2 non-planar forms were calculated in gas phase at distinct ab initio levels of theory. The C 2 structure was found to be the global minimum, being only 0.50 kcal/mol lower in energy than the D 6h isomer at the MP4(SDQ)/6-311+G(2d)//MP2/6-311+G(2d) level. When the thermal correction and solvent effect were included in the relative Gibbs free energy, the C 2 isomer was found to be more favourable by ∼3 kcal mol −1. The D 6h form is a stationary point with three imaginary frequencies. The infrared and Raman spectra were reported and band assignments made for both isomers, showing that these techniques are not conclusive to identify the form of the rhodizonate ion present in the medium. The effect of the counter ion (Li +) on the structure and equilibrium position was also investigated, showing that the coordination with this metal stabilizes the non-planar C 2 form.