Bonding in SCl_<i>n</i> (<i>n</i> = 1−6): A Quantum Chemical Study

Following a previous study of bonding and isomerism in the SF_<i>n</i> and singly chloro-substituted SF_<i>n</i>−1Cl (<i>n</i> = 1−6) series, we describe bonding in the ground and low-lying excited states of the completely substituted series, SCl_<i>n</i> (<i>n</i> = 1−6). All structures were characterized at least at the RCCSD(T)/aug-cc-pV(Q+d)Z level of theory. Both differences and similarities were observed between SCl_<i>n</i> and our previous results on SF_<i>n</i>−1Cl and SF_<i>n</i>. Several minimum structures that exist in SF_<i>n</i> and SF_<i>n</i>−1Cl are absent in SCl_<i>n</i>. For example, the optimized structure of SCl₂(³A₂) is a transition state in <i>C</i>_<i>s</i> symmetry, whereas the analogous states are minima in SF_<i>n</i> and SF_<i>n</i>−1Cl. Second, we found a continuation of a trend discovered in the SF_<i>n</i>−1Cl series, where Cl substitution has a destabilizing effect that weakens bonds with respect to SF_<i>n</i>. This effect is much stronger in the SCl_<i>n</i> series than it is in the SF_<i>n</i>−1Cl series, which is why SCl₂ is the most stable observed species in the family and why SCl₄, SCl₅, and SCl₆ are unstable (SCl_<i>n</i>−2 + Cl₂ additions are endothermic for <i>n</i> = 4−6).