Are the structures of C2Sn- (5 ≤ n ≤ 8) clusters featured by two connected carbons or by two separated carbons?

► Isomers of C2Sn- (5 ≤ n ≤ 8) clusters were studied at B3LYP level. ► The bond energy of CC is stronger than that of CS by 65 kJ/mol. ► However, the structures with two separated carbons on the ring (VI) are more stable than that with two connected carbons on the ring (I) due to release of ring strain. ► The additional stabilized factors are the formation of weak S⋯S bond and negative charge's delocalization relative to other isomers.