On the quest of heterometallic mixed-valence MM'X chains, we have prepared two stable discrete bimetallic compounds: the reduced (PPN)[ClNi(mu-OSCPh)(4)Pt] (PPN = bis(triphenylphosphine)iminium; OSCPh = benzothiocarboxylato) and the oxidized [(H2O)Ni(mu-OSCPh)(4)PtCl] species. The role of the aqua and chlorido axial ligands is crucial to facilitate oxidation of the {Ni(mu-OSCPh)(4)Pt} core. Experimental and theoretical analyses indicate that a NiPt-Cl/Cl-NiPt isomerization process occurs in the oxidized species. The electronic structure of the reduced system shows two unpaired electrons, one located in a d(x2-y2) orbital of the Ni(II) ion and a second in the antibonding d(z2-dz2) combination from the Ni(II) and Pt(II) centers. Oxidation occurs by removing one electron from this second multicenter molecular orbital. Although the mixed-valence character of the oxidized species makes the isolation of MM'X chains very attractive, such polymeric structure is prevented by the low Pt-Cl center dot center dot center dot Ni interaction energy and the high tendency of Ni centers to coordinate water molecules. Thus, this work offers valuable insights and hints to engage the production of heterometallic mixed-valence MM'X chains, which still is a challenging task.