On the quest of heterometallic mixed-valence MM'X chains, we have prepared two stable discrete bimetallic compounds: the reduced (PPN)[ClNi(μ-OSCPh)4Pt] (PPN = bis(triphenylphosphine)iminium; OSCPh = benzothiocarboxylato) and the oxidized [(H2O)Ni(μ-OSCPh)4PtCl] species. The role of the aqua and chlorido axial ligands is crucial to facilitate oxidation of the {Ni(μ-OSCPh)4Pt} 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 dx(2)-y(2) orbital of the Ni(II) ion and a second in the antibonding dz(2)-dz(2) 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···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.