INFRARED EVIDENCE FOR CO2 ELECTRON-DONOR ACCEPTOR COMPLEXES

Frequencies and bandwidths of the nu3(CO2) (asymmetric stretching) and nu2(CO2) (bending) vibration bands were determined by IR spectroscopy for CO2 dissolved in more than 35 organic solvents. Two nu2(CO2) bands appear for CO2 solutions in tertiary amides, tertiary amines and DMSO, and the same seems to be true for ketones and esters. The nu2(CO2) band at lower wavenumbers was assigned to CO2-n-electron donor complexes. In such complexes the electron donor's lone pair is directed to the CO2 carbon atom. The possibility of formation of electron donor-acceptor (EDA) complexes of CO2 with pi-electron donors is also considered.