Platinum(III) is no longer an uncommon oxidation state. Numerous binuclear platinum(III) complexes have been prepared and structurally characterized over the past eight years. These include sulfate‐bridged dimers of D4h symmetry, [Pt2(SO4)4L2]2−, L = H2O, DMSO; phosphate‐bridged complexes [Pt2(HPO4)4‐(H2O)2]2− and [Pt2(H2PO4)(HPO4)3(py)2]−; POP (H2 P2 O2− 5)‐bridged ions [Pt2‐(POP)4X2]2−, X = halide; an extensive series of α‐pyridonate (C5H4NO−)‐bridged head‐to‐head and head‐to‐tail complexes, [Pt2(NH3)4 (C5H4NO)2XY]n−, X, Y = NO3, NO2, H2O, Cl, Br; n = 2, 3; and organometallic derivatives such as [Pt2(CH3)4‐(CF3CO2)2(4‐Mepy)2]. In all cases there is a Pt–Pt single bond of length 2.47–2.7 Å, pseudo‐octahedral geometry about platinum, and two or more bridging ligands. The complexes are stable in solution and some undergo quasi‐reversible two‐electron redox reactions. Mononuclear platinum(III) complexes are less well characterized structurally, but have been stabilized in diamagnetic host lattices in the solid state and by macrobicyclic cage ligands in solution following pulse radiolytic or γ‐irradiation of precursor platinum(II) complexes. The first unequivocal, crystallographically characterized mononuclear platinum(III) complex, [Pt(C6Cl5)4]−, has just been reported.
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