Are the structures of (5 n 8) clusters featured by two connected carbons or by two separated carbons?

Despite the bond energy of CC is stronger than that of CS by 65 kJ/mol, the structure of C 2 S n - (5 ≤ n ≤ 8) clusters with two connected carbons on the ring (I) are revealed to be less stable than the structure with two separated carbons on the ring (VI) at B3LYP level. This can be rationalized by that the energy benefit from CC bond is less than that loss caused by ring strain arising from this bond in the structure I. Besides release of ring strain, the formation of weak S⋯S bond and negative charge’s delocalization are also revealed to be related to the stability of the ground-state structure VI.