A gas- and condensed-phase density functional study of donor-acceptor complexes of sulfur trioxide.

A series of donor−acceptor complexes containing sulfur trioxide have been studied in the gas and condensed phases using density functional theory. The condensed phase is represented using the polarizable continuum model. The systems investigated include complexes of nitrogen-containing donor molecules, (CH3)nH3-nN (n = 0−3), with SO3 and complexes of oxygen-containing donor molecules, (CH3)mH2-mO (m = 0−2), with SO3. Significant differences are observed between the gas- and condensed-phase properties of the complexes as a result of the ability of the condensed-phase medium to support higher charge separation between the donor and acceptor. The gas/condensed-phase behavior of two nitrogen-containing complexes, (CH3)H2N−SO3 and (CH3)2HN−SO3, has been investigated for the first time. These complexes exhibit properties intermediate to the previously observed H3N−SO3 and (CH3)3N−SO3 complexes. Systematic trends in the gas- and condensed-phase structure and properties have been observed as methyl groups are add...