A one-dimensional iodine-bridged PtII/PtIV mixed-valence complex, catena-poly[[[bis(ethylenediamine)-platinum(II)]-μ-iodo-[bis(ethylenedi- amine)platinum(IV)-μ-iodo] hydrogenphosphate dihydrogenphosphate iodide trihydrate]

The title compound, {[(PtPtI2)-Pt-II-I-IV(C2H8N2)(4)](HPO4)(H2PO4)I center dot 3H(2)O}(n), has a chain structure composed of square-planar [Pt(en)(2)](2+) and elongated octahedral trans-[PtI2(en)(2)](2+) cations (en is ethylenediamine) stacked alternately along the c axis and bridged by the I atoms; a three-dimensionally valence-ordered system exists with respect to the Pt sites. The title compound also has a unique cyclic tetramer structure composed of two hydrogenphosphate and two dihydrogenphosphate ions connected by strong hydrogen bonds [O center dot center dot center dot O = 2.522 (10), 2.567 (10) and 2.569 (11) angstrom]. The Pt and I atoms form a zigzag center dot center dot I-Pt-IV-I center dot center dot Pt-II center dot center dot center dot chain, with Pt IV-I bond distances of 2.6997 (7) and 2.6921 (7) angstrom, interatomic Pt-II center dot center dot center dot distances of 3.3239 (8) and 3.2902 (7) angstrom, and Pt-IV-I center dot center dot Pt-II angles of 154.52 (3) and 163.64 (3)degrees. The structural parameters indicating the mixed-valence state of platinum, expressed by delta = (Pt-IV-I)/(Pt-II-I), are 0.812 and 0.818 for the two independent I atoms.