Two nickel complexes with metallodithiolate ligands, which can be regarded as the active site models of the acetyl coenzyme A synthase, were prepared and structurally characterized by X-ray crystallography. Reactions of Ni(PPh3)(2) Cl-2 with Ni(bme-dach) [bme-dach = N, N'-bis( mercaptoethyl)-1,4-diazacycloheptane] or Ni(bme-dach*) [bmedach* = N, N'-bis(mercaptoethyl)-1,4-diazacyclohexane] in MeCN in the presence of NH4 PF6 resulted in the formation of a trinuclear nickel complex {Ni[Ni(bme-dach)](2)}[PF6-](2) (1) and a hexanuclear nickel complex {Ni-2 [Ni(bme-dach*)](4)}[PF6-](4) (2). The crystal structure of 1.2MeCN shows a square planar geometry of nickel atom that is coordinated by four sulfur atoms of the metallodithiolate ligands Ni(bme-dach). The crystal structure of 2.4MeCN reveals that each of the two nickel atoms is ligated by four sulfur atoms of the metallodithiolate ligands Ni(bme-dach*) to form a square planar coordination sphere.