A novel AuICoIII coordination system that is derived from the newly prepared [Co(D-nmp)2]− (1−; D-nmp=N-methyl-D-penicillaminate) and a gold(I) precursor AuI is reported. Complex 1− acts as a sulfur-donating metallaligand and reacts with the gold(I) precursor to give [Au2Co2(D-nmp)4] (2), which has an eight-membered AuI2CoIII2 metallaring. Treatment of 2 with [Au2(dppe)2]2+ (dppe=1,2-bis(diphenylphosphino)ethane) leads to the formation of [Au4Co2(dppe)2(D-nmp)4]2+ (32+), which consists of an 18-membered AuI4CoIII2 metallaring that accommodates a tetrahedral anion (BF4−, ClO4−, ReO4−). In solution, the metallaring structure of 32+ is readily interconvertible with the nine-membered AuI2CoIII metallaring structure of [Au2Co(dppe)(D-nmp)2]+ (4+); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the AuS and AuP bonds, which is essential for metallaring expansion and contraction.