Structures of [(CO2)n(CH3OH)m]− (n = 1−4, m = 1, 2) Cluster Anions

The infrared photodissociation spectra of [(CO2)n(CH3OH)m]- (n = 1－4, m = 1, 2) are measured in the 2700－3700 cm-1 range. The observed spectra consist of an intense broad band characteristic of hydrogen-bonded OH stretching vibrations at ≈3300 cm-1 and congested vibrational bands around 2900 cm-1. No photofragment signal is observed for [(CO2)1, 2(CH3OH)1]- in the spectral range studied. Ab initio calculations are performed at the MP2/6-311++G** level to obtain structural information such as optimized structures, stabilization energies, and vibrational frequencies of [(CO2)n(CH3OH)m]-. Comparison between the experimental and theoretical results reveals the structural properties of [(CO2)n(CH3OH)m]-: (1) the incorporated CH3OH interacts directly with either CO2- or C2O4- core by forming an O－H・・・O linkage; (2) the introduction of CH3OH promotes charge localization in the clusters via the hydrogen-bond formation, resulting in the predominance of CO2-・(CH3OH)m(CO2)n-1 isomeric forms over C2O4-・(CH3OH)m(CO2)n-2; (iii) the hydroxyl group of CH3OH provides an additional solvation cite for neutral CO2 molecules.
This is a preprint of an article published by American Chemical Society in Journal of Physical Chemistry A, 2008, available online: http://pubs.acs.org/doi/abs/10.1021/jp800289g.
This work was supported by Grants-in-Aid for Scientific Research (Grant Nos. 18550007 and 19029011) from Japan Society for the Promotion of Science (JSPS), and from the Ministry of Education, Culture, Sports, Science and Technology (MEXT).