Bonding in SCl_n (n = 1-6): A quantum chemical study

Following a previous study of bonding and isomerism in the SF_n and singly chloro-substituted SF_n-1Cl (n = 1-6) series, we describe bonding in the ground and low-lying excited states of the completely substituted series, SCl_n (n = 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_n and our previous results on SF_n-1Cl and SF_n. Several minimum structures that exist in SF_n and SF_n-1Cl are absent in SCl_n. For example, the optimized structure of SCl₂(³A₂) is a transition state in C_s symmetry, whereas the analogous states are minima in SF_n and SF_n-1Cl. Second, we found a continuation of a trend discovered in the SF_n-1Cl series, where Cl substitution has a destabilizing effect that weakens bonds with respect to SF_n. This effect is much stronger in the SCl_n series than it is in the SF_n-1Cl series, which is why SCl₂ is the most stable observed species in the family and why SCl₄, SCl₅, and SCl₆ are unstable (SCl_n-2 + Cl₂ additions are endothermic for n = 4-6).