Infrared spectroscopic and computational studies of Co(ClO) dissolved in N,N-dimethylformamide (DMF). Vibrations of DMF influenced by Co or ClO or both.

Infrared (IR) spectroscopy for N,N-dimethylformamide (DMF) shows that the OCN bend (δ) and the CO stretch (ν) vibrations undergo an upshift and a downshift, respectively, on the dissolution of Co(ClO). Quantum chemical calculations are performed for optimizing the structures and predicting the IR spectra of model complexes for solute species. The calculations reveal that Co exerts a much larger influence than ClO on the vibrations of DMF. For Co(DMF), in which each DMF molecule is coordinated to Co via the O atom, the Co⋯DMF interaction upshifts the δ frequencies (+24 cm on average) while the dipole coupling gives rise to splitting (12 cm) of the modes. On the other hand, the Co⋯DMF interaction downshifts the ν frequencies (-15 cm on average) while the splitting of the modes amounts to 37 cm. As a result, one of the ν modes is located at an upshifted position (+13 cm) despite the O-atom coordination. For six-coordinated isomers of Co(DMF), the δ and ν frequencies of the second-sphere DMF are close to those of bulk DMF in neat liquid. The calculations indicate that it is difficult to prove or exclude the formation of contact ion pairs [Co(DMF)ClO] and solvent-shared ion pairs [Co(DMF)ClO] by IR spectroscopy in the δ and ν regions. However, asymmetric ClO stretches of the ClO moiety suggest that conceivable is the coexistence of solvent-shared ion pairs only.