In our search for novel main-group-based redox-active platforms for solar fuel production, we have synthesized (Cl2SbPtCl3)-Pt-IV-Cl-III(o-dppp)(2) (2, o-dppp = o-(Ph2P)C6H4)), a complex featuring a highly oxidized [PtSb](VII) core. This thermally stable complex quickly evolves chlorine upon irradiation with a Xe lamp, leading to [(Cl2SbPtCl)-Pt-IV-Cl-I(o-dppp)(2)] (1) as the photoproduct. This photoreduction is very efficient, with a maximum quantum yield of 13.8% when carried out in a 4.4 M solution of 2,3-dimethyl-1,3-butadiene in CH2Cl2. Remarkably, 2 also evolves chlorine when irradiated in the solid state under ambient conditions in the absence of a trap.