Square-planar copper(II) and nickel(II) derivatives of the cis-dithiolate N2S2 ligand bis(N,N'-2-mercapto-2-methylpropyl)1,5-diazocyclooctane, (bme*daco)M, nucleate four (CuCl)-Cl-I moieties, forming (M2Cu4S4)-Cu-II-S-I clusters with unusual triply bridging thiolates, mu(3)-SR, in the topological form of adamantane. As determined by X-ray crystallography, the (bme*daco)M (M = Cu or Ni) metallothiolate serves as a bidentate ligand that bridges four Cu-I ions, utilizing all lone pairs on sulfurs. Further characterization by electrochemical and electronic spectral measurements suggests greater electron delocalization in the all-copper complex as compared to the NiCu heterometallic complex. Mass spectral data imply that the mixed-metal (Ni2Cu4S4)-Cu-II-S-I is more stable toward CuCl loss than (Cu2Cu4S4)-Cu-II-S-I, a result that is corroborated by extraction of Cu-I by 1,2-bis(diphenylphosphino)ethane in the latter but not the former.