Abstract: | The title compound, catena‐polybis(ethylenediamine‐κ2N,N′)platinum(II)]‐ μ‐chlorido‐bis(ethylenediamine)platinum(IV)]‐μ‐chlorido] tetrakis{4‐(4‐hydroxyphenyl)diazenyl]benzenesulfonate} dihydrate], {PtIIPtIVCl2(C2H8N2)4](HOC6H4N=NC6H4SO3)4·2H2O}n, has a linear chain structure composed of square‐planar Pt(en)2]2+ (en is ethylenediamine) and elongated octahedral trans‐PtCl2(en)2]2+ cations stacked alternately, bridged by Cl atoms, along the b axis. The Pt atoms are located on an inversion centre, while the Cl atoms are disordered over two sites and form a zigzag ...Cl—PtIV—Cl...PtII... chain, with a PtIV—Cl bond length of 2.3140 (14) Å, an interatomic PtII...Cl distance of 3.5969 (15) Å and a PtIV—Cl...PtII angle of 170.66 (6)°. The structural parameter indicating the mixed‐valence state of the Pt atom, expressed by δ = (PtIV—Cl)/(PtII...Cl), is 0.643. |