Li⁺CO₂^- and Na⁺CO₂^- generated in argon matrices: An ESR study

Li+CO2- and Na+CO2- charge-transfer complexes were generated by cocondensation of alkali-metal atoms and CO2 molecules in argon matrices at ∼4 K. The ESR spectra of Li+CO2- of both the Cs form and the cyclic C2v form and Na+CO2- of the C2v form were observed. The g-tensors, the 13C hyperfine coupling tensors, and the alkali-metal atom hyperfine coupling tensors of the C2v complexes were determined. The unpaired electron distribution (∼55% at C and ∼35% at two oxygen atoms of the CO2 moiety and ∼10% at the alkali-metal atom) determined from these hfc tensors is in good agreement with that given by the MNDO molecular orbital method. In the case of the Li/CO2/Ar system, a strong orientation effect was observed for the resulting Li+CO2- complexes. The orientation mechanism consistent with the observed effect is presented and demonstrated. © 1994 American Chemical Society.